key: cord-0776309-5widjq70
authors: Rajak, Prem; Ganguly, Abhratanu; Sarkar, Saurabh; Mandi, Moutushi; Dutta, Moumita; Podder, Sayanti; Khatun, Salma; Roy, Sumedha
title: Immunotoxic role of Organophosphates: an unseen risk escalating SARS-CoV-2 pathogenicity
date: 2021-01-23
journal: Food Chem Toxicol
DOI: 10.1016/j.fct.2021.112007
sha: bdf2c028b17cc2f46f1ae26bb01de25a91f70583
doc_id: 776309
cord_uid: 5widjq70

Consistent gathering of immunotoxic-substances on earth is a serious global-issue affecting people under pathogenic-stress. Organophosphates are among such hazardous-compounds that are ubiquitous in nature. They fuel oxidative-stress to impair antiviral immune-response in living-entities. Aside, organophosphate ignites cytokine-burst and pyroptosis in broncho-alveolar chambers leading to severe respiratory-ailments. At present, we witness COVID-19 outbreak caused by SARS-CoV-2. Infection triggers cytokine-storm coupled with inflammatory-manifestations and pulmonary-disorders in patients. Since organophosphate-exposure promotes necroinflammation and respiratory-troubles hence during current pandemic-situation, additional exposure to such chemicals can exacerbate inflammatory-outcome and pulmonary-maladies in patients, or pre-exposure to organophosphates might turn-out to be a risk-factor for compromised-immunity. Fortunately, antioxidants alleviate organophosphate-induced immunosuppression and hence under co-exposure circumstances, dietary-intake of antioxidants would be beneficial to boost immunity against SARS-CoV-2 infection.

With the advancement of scientific-revolution, human beings have made the existing anthropocene more comfortable for their daily-life. From agricultural-field to the industrialsector, human populations are blessed with the use of modern technologies and equipments, which not only reduce energy for production but also enhance yield at the same time. But the darker-side of such advancement includes consistent gathering of detrimental chemicals in the environment contaminating almost every component of biosphere. These chemicals have secured their apparent presence in several drugs, food stuffs, household products, drinking water, agrochemicals and so on. Organophosphates (OPs) are among such hazardous compounds that are being globally used on a regular-basis.

OPs are amides, esters, or thiol derivatives of phosphoric acid. These chemicals are extensively used in agriculture, horticulture, forestry, veterinary-medicine, domestic purpose and also for the control of vector-borne diseases. Certain OPs are being used to treat head-lice, scabies and crablice in humans (Idriss, & Levitt, 2009 ). In agricultural-sector, OPs are extensively applied to eradicate pests including locusts, aphids, leaf-miners, fire-ants, thrips and caterpillars. These pesticides augment both quantity and quality of agricultural-products (Chang et al., 2017) . OPs namely tris-(2-chloro,1-methyl-ethyl)-phosphate, tris-(2-chloroethyl)-phosphate, tri-n-mortality by infectious diseases (Hayashi et al., 2013; Fournier et al., 1998) . Intoxication with cypermethrin impedes antibody forming ability of B-lymphocytes and cell mediated immune responses (Tamang et al., 1998 ) that may disrupt anti-SARS-CoV-2 defense reactions. Exposure to carbamates is followed by hypersensitivity reactions, autoimmune diseases and even cancers.

They often invite immunopathology by inducing mutations in genes encoding for immunoregulatory factors and modifying immune tolerance (Dhouib et al., 2016) . Short term exposure to atrazine, a widely used herbicide decreases thymic and spleenic cellularity coupled with subverted native T-helper and cytotoxic T-cells (CTL). It is important to note that, immunotoxic impacts of atrazine can persist for longer duration even after termination of the exposure (Filipov et al., 2005) .

OP pesticides are not ideal because they lack target-specificity and often fuel health hazards including immunotoxicity in humans. Nevertheless, agricultural uses of OP pesticides are gaining popularity and they account for more than 30% of global insecticide sales. It is to be noted that, the global market of OP pesticide is expected to exhibit a compound annual growth rate of 5.5% during the forecast period 2018-2023 (https://www.mordorintelligence.com/industryreports/organophosphate-pesticides-market) and this could enhance human-OP encounter during the current pandemic situation. Unfortunately in many of the developing countries, OPs are being indiscriminately used in agriculture that could further amplify unintentional exposure to these compounds and suppress immunity against viral infections including SARS-CoV-2.

At present, world is struggling to overwhelm outbreak of coronavirus disease-19 caused by SARS-CoV-2. The disease was first identified in Wuhan of Hubei province, China in To curb SARS-CoV-2 infection, a healthy immune system is obligatory despite of potent vaccine to alleviate morbidities in patients. But unintentional exposure to OP compounds from several sources can rupture the antiviral defense against SARS-CoV-2. Moreover respiratory ailments may also be fueled by OP compounds. Hence, SARS-CoV-2 mediated morbidities and fatalities could be backed by unintentional exposure to OPs in patients.

Current review will cover structure, transmission-pattern and respiratory-immunopathologies of SARS-CoV-2 in infected patients. In addition, immunotoxic impacts of wide-spread OP compounds on human and animal models will also be enumerated citing major in vivo and in vitro findings. At the end, immuno-protective nature of certain antioxidants will be discussed.

These antioxidants would be beneficial in mitigating pathologies that may arise following coexposure to SARS-CoV-2 and OP compounds.

RNA. It also antagonizes interferon (IFN) response and RNA-silencing in host-cell (Cui et al., 2015) . M-glycoprotein is the most abundant envelope-protein that helps to maintain sphericalmorphology of virion (Neuman et al., 2011) . E-protein is involved in viral-assembly, release and pathogenesis (Nieto-Torres et al., 2014) . S (Spike) protein assembles into trimer on virionsurface to obtain a distinctive "corona" or crown-like appearance (Wrapp et al., 2020) . S-protein is comprised of trimeric S1 heads sitting on the top of trimeric S2 stalk. S1 contains a receptorbinding-domain (RBD) that strongly recognizes host angiotensin converting enzyme-2 (ACE-2) receptors. RBD constantly switches between a standing-up position for receptor binding and a lying-down position for immune-evasion (Shang et al., 2020) . S2 harbors a fusion-peptide (FP;

5-25 amino-acids) and two heptad-repeat (HR1 & HR2) regions involved in fusagenic events between viral-envelope and host cell-membrane (Henning, & Pillat, 2020) . S1/S2 interface contains a proprotein convertase (PPC) motif that needs to be activated by proteases for effective entry into host-cell (Shang, et al., 2020) .

Cell-invasion by virions is governed by precise interaction between S-proteins and ACE-2 receptors on host-cell. SARS-CoV-2 may also interact with CD147-receptor to invade the targetcell (Henning & Pillat, 2020) . Binding of S1 to the ACE-2 receptor promotes proteolyticactivation of PPC motif at S1/S2 interface via cumulative action of surface proteases-TMPRSS2

and furin (Hoffmann et al., 2020; Hasan et al., 2020) . Such proteolytic activation invokes a conformational change in S2 exposing FP. Hydrophobic amino-acid residues of FP insert themselves into the host cell-membrane to acquire a hairpin-loop confirmation. Following the event, both HR1 and HR2-domains fold via their hydrophobic-grooves into an antiparellel 6helical bundle to make a stable fusion-core . These key steps pull-down the viral-membrane in close proximity of host cell-membrane to mediate viral-host cell fusion and J o u r n a l P r e -p r o o f transfer of genomic-RNA therein. Within cytosolic moiety, SARS-CoV-2 virions are replicated, packaged and thereafter exocytosed out of the cell to infect the fresh one ( Fig. 1) .

In the present pandemic milieu, our immune-system provides best defense against the coronavirus-infection. SARS-CoV-2 stimulates various components of innate and adaptive immunity that are involved in clearance of viral particles out of the body.

Innate immunity constitutes the first line of defense against viral infections. Population of immunocytes of myeloid lineage tends to increase during COVID-19. In a study of 61 COVID-19 patients, blood neutrophil count and neutrophil-to-lymphocyte ratio were significantly higher in severe cases . In another study, remarkably higher proportions of activated mast cells and neutrophils were observed in the bronchoalveolar lavage fluid (BALF) of COVID-19 patients indicating active participation of these immunocytes against SARS-CoV-2 (Zhou et al., 2020c) . Complement system plays crucial role in innate defense against wide spectrum of pathogens. have demonstrated that, serum level of complement proteins increases in severe COVID-19 patients compared to mild cases and healthy controls.

Additionally, an enrichment in gene expression associated with complement activation and the classical pathway has been observed in infected patients (Xiong et al., 2020) . Interferons (IFNs) are signaling molecules produced in response to viral infection to exert strong anti-viral immune response. Unfortunately, SARS-CoV-2 infection dampens the IFN synthesis that could rupture innate defense system (Acharya et al., 2020) . Concurrently, SARS-CoV-2 infection triggers profound synthesis of proinflammatory cytokines to execute cytokine-storm and pyroptosis. Excessive secretion of proinflammatory-chemokines namely IL-1β, IL-2, IL-6, IL--7, G-CSF, IP-10, MCP-1, MIP-1, TNFα and IL1RA hyper-stimulates the innate defense that could exaggerate immunopathologies by several folds in COVID-19 patients. (Blanco-Melo et al., 2020; Chu et al., 2020; .

Considering the above facts, it can be speculated that, myeloid cells and complement system play major role to restrict SARS-CoV-2 infection. However, suppressed/delayed IFN-response can dampen early viral-control leading to massive efflux of proinflammatory-cytokines. Such detrimental consequences promote respiratory-illness including pneumonia, bronchitis and acute respiratory distress syndrome (ARDS). Hence, healthy innate immune-response is vital to restrain SARS-CoV-2 mediated disease-progression.

Transition from innate to adaptive immune-response is important for clinical progression of coronavirus-infection. T-lymphocytes orchestrate the adaptive immune-responses involved in clearance of virally infected-cells. NK-cells, INF-γ-secreting T-cells and Spike RBD-specific Tcells govern cell-mediated immune-response against SARS-CoV-2 infection (Ni et al., 2020) .

Healthy population of cytotoxic CD8-cells is required to eliminate virally infected cells out of the body (Li et al., 2020a) . Reduced activation of B-cells and dendritic-cells (DCs) are implicated in disease-progression and pathological-outcome in patients .

Antibody-mediated immune response is essential for recovery from COVID-19. Nucleocapsid protein (NP)-specific antibody response was reported in infected patients suggesting their active participation in humoral immune-response (Zhou et al., 2020a) . Ni et al. (2020) 

Immunotoxicity is defined as an adverse effect on integral components of immune system resulting in immunosuppression or exaggerated immune responses. Immunotoxicity can augment the incidences of being virally infected and/ hyper-stimulate the immune components to target body's own healthy tissues. Current evidences have classified these effects into three broad categories namely direct immunotoxicity, hypersensitivity and autoimmunity. OP compounds are potential modulators of immune system. Adequate volume of in vitro (table 1), in vivo (table 2) and direct evidences on human (table 3) have unmasked the immunotoxic feature of OPs and their metabolites. Documented immunotoxicity as imposed by OP compounds on cell culture setups, animal models and human includes the following:

Immune system is comprised of distinct lymphoid organs that support development, maturation and function of immunocytes. These organs are classified into primary and secondary lymphoid organs. Primary lymphoid organs include red bone marrow and thymus where production, clonal selection and maturation of lymphocytes occur whereas secondary lymphoid tissues such J o u r n a l P r e -p r o o f as spleen, lymph nodes, Peyer's patches and mucosa associated lymphoid tissue (MALT) provide space for lymphocyte-antigen interaction. Therefore, these organs can determine the cumulative status of immune health in human and other animals.

Numerous studies have revealed the toxic outcome of OP-exposure on lymphoid organs. For instance, dimethoate was reported to reduce thymic cortex and damage thymocytes in rodents (Tiefenbach and Lange, 1980) . Handy et al. (2002) monitored the impact of diazinon-exposure on rodent lymphoid-tissues. Study indicated that, diazinon promotes necrosis in trabeculae of spleen and thymus coupled with hyperplasia of cortical-medullary zones of lymph-nodes. Aside, hyperplasia in red and white-pulp of spleen was also noticed. Intra-peritoneal administration of diazinon inflicted atrophy in thymus and spleen with suppressed splenocyte-proliferation in C57bl/6 female mice (Neishabouri, 2004) . Malathion reduces weight and cellularity of major lymphoid organs in rodents (Ramadan et al., 2017) . In a separate study, malathion was responsible for degeneration of spleenic lymphatic follicles and bone marrow cells in juvenile male rats (Ahmed, 2012) . Intoxication with other OPs like azamethiphos, chlorfenvinphos, chlorpyrifos-oxon, diazinon-oxon, dichlorvos and malaoxon promotes thymic protein adduction to render functional impairment (Carter et al., 2007) . Shahzad et al. (2015) through their study reported chlorpyrifos-induced disorganization of follicular patterns, severe congestion, cytoplasmic vacuolation, degeneration and hyperplasia of spleenic reticular cell whereas necrosis in thymic myoid cell. Swiss albino mice exposed to aqueous mixture of profenofos, and chloropyrofos for 13 weeks manifested distortion in bone marrow architecture characterized by deformed stromal matrix and stromal cells. Moreover, a quantitative depression in the primitive bone marrow stem cells was evident following OP insult (Chatterjee et al., 2014). Intra-peritoneal injection of acephate down-regulates the serum CD4, CD8, B-cell and monocyte contents in rodents (Singh & Jiang, 2003) . Nain et al. (2011) investigated the effect of malathion on immune-system of Japanese-quail. They observed bursal-atrophy and reduced B-cell density in OP-treated birds. Experiment by Gallicchio et al. (1987) showed that, primary metabolites of parathion and malathion generate dose dependent depression in colony formation by granulocyte-macrophage progenitor cells of bone marrow leading to sub-population of active immune cells. In a case study, individuals dealing with chlorpyrifos were reported to have reduced population of CD5 + lymphocytes in their blood-samples (Thrasher et al., 2002; Thrasher et al., 1993) . Sub-chronic exposure of the male swiss albino mouse to recommended field dose of Thimet (Phorate) caused significant decrease in lymphocyte content (Morowati et al., 1997) .

Similarly, Lima and Vega (2005) reported that, exposure to methyl parathion reduces proliferation of human peripheral blood mononuclear cells.

Immunocytes have their distinct function to orchestrate cell mediated and humoral immune responses against numerous microbial pathogens including SARS-CoV-2. Nevertheless, studies have fueled global concern regarding the modulation of anti-viral immunity by OP compounds.

Study by Rodgers and Xiong (1997) have revealed that, repeated administration of malathion alters macrophage function and mast cell degranulation in mice. Similarly, exposure to dimethyl 2,2-dichlorovinyl phosphate reduces activity of natural killer (NK) cells, lymphokine-activated killer (LAK) cells and CTL in a dose-dependent manner (Tang et al., 2003) . Other OP J o u r n a l P r e -p r o o f compounds for instance, triphenylphosphine oxide and tetra-o-cresylpiperazinyl diphosphoamidate hinder monocyte-mediated antigen presentation and lymphocyte proliferation in human mononuclear cells (Esa et al., 1988) . In a study, Hermanowicz and Kossman (1984) analyzed neutrophil-function and prevalence of infections in 85 workers exposed to phosphoorganic pesticides. They observed reduced neutrophil-chemotaxis and adhesion properties in these workers compared to unexposed-group. In addition, upper respiratory-tract infection was frequent in exposed-workers. In another study, treatment with difenphos and glyphosate suppressed proliferative response of splenocytes towards mitogens; phytohemagglutinin (PHA) and concanavalin A (Con A) in Tilapia nilotica pointing towards injured cell-mediated immunity (el-Gendy et al., 1998) . Exposure to monocrotophos reduces active splenic macrophages in broiler chicks (Garg et al., 2004) . Administration of chlorpyrifos to rats at a dose of 5.0 mg/kg for 28 days suppressed humoral immune response and Tlymphocyte blastogenesis induced by concanavalin A and phytohemagglutinin (Blakley et al., 1999) . In vitro exposure of diazinon reduces phagocytic activity of macrophage-like RAW264.7

cells (Ogasawara et al., 2017) . Neutrophil function in 40 workers occupationally exposed to OP pesticides was disrupted to some extent (Queiroz et al., 1999) . Zabrodskii (2018) found that, chronic intoxication of rats with malathion and parathion methyl (0.01 LD 50 daily, for 30 days)

significantly reduces the phagocytic-metabolic activity of neutrophils and NK cells. Li et al. (2020b) have reported that, Triphenyl phosphate and Tris (2-butoxyethyl) phosphate partially attenuate the adhesion and phagocytic potential of the THP-1 mφs. In the same study, Tris (1,3dichloropropan-2-yl) phosphate was documented to catalyze functional loss of macrophages.

Triphenylphosphate and Tris (1,3-dichloroisopropyl) phosphate exposure (Canbaz et al., 2017).

Moreover, Tris (1,3-dichloropropan-2-yl) phosphate promotes functional loss of Human-THP-1 derived macrophages.

Healthy antibody titer is essential to curb SARS-CoV-2 infections. Certain OP compounds are responsible for low antibody-titer (Li et al., 2000; Fautz and Miltenburger, 1994) and hence can potentially augment the risk for viral infections including COVID-19. Suke et al. (2006) treated albino-rats with phosphamidon and measured low serum antibody-titer and macrophage migration. In another study, reduced level of IgG plaque forming cells was reported in inbred mice exposed to parathion (Casale et al., 1984) . Malathion at noncholinergic doses suppressed generation of rodent IgM and IgG antibodies against sheep red blood cell (SRBC) (Rodgers et al., 1996) . A recent study has demonstrated the impaired Th-2 lymphocyte function and IgG production in albino rats acutely intoxicated with malathion (Zabrodskii, 2019 (Ibrahim, 2014) .

Cytokines are endogenous low molecular weight soluble proteins that are produced in response to antigens and function as chemical messengers to drive innate and adaptive immune responses.

Two major groups namely proinflammatory and anti-inflammatory cytokines orchestrate controlled immune response. Proinflammatory cytokines are activated in response to antigenic insult and provide effective defense against exogenous pathogens. Nevertheless, overproduction of these mediators fuel intense inflammatory reactions that can be detrimental to multiple organs.

In contrast, anti-inflammatory cytokines down-regulate exacerbated inflammatory process and maintain cytokine homeostasis for proper functioning of vital organs. Several literatures have advocated the implication of OPs in dyshomeostasis of cytokine response in cell culture set-ups, animal models and human.

In a very recent study, Tris (2-methylphenyl) phosphate has been reported to inhibit antiinflammatory cytokines that can disrupt cytokine balance . Decreased immunocompetence with a relevant increase in IL-22 concentration was reported in 64 greenhouse workers exposed to OP pesticides (Fenga et al., 2014) . Diethyldithiophosphate (DEDTP) is a metabolite formed by biotransformation of OP pesticide and has a longer half-life than its parent compound. Esquivel-Sentíes et al. (2010) showed that, human CD4 + T lymphocytes exposed to DEDTP (1-50μM) had lower secretion of IL-2, IFN-γ and IL-10. Authors suggested that, DEDTP can modulate phosphorylation of suppressor of cytokine signaling-3 (SOCS3) which acts as negative regulator of cytokine signaling. Results from a cytokine/chemokine secretion analysis revealed the proinflammatory properties of Tris (1,3-dichloropropan-2-yl) phosphate, Triphenyl phosphate, and Tris (2-butoxyethyl) phosphate . These compounds reduce the production of anti-inflammatory cytokines (IL-10 and IL-13) and trigger the release of proinflammatory cytokine (TNF-α). In another study, exposure to chlorpyrifos suppressed production of IFN-γ, TNF-α and IL-6 following LPS stimulation in mice (Singh et al., 2013) . In vitro study by has claimed that, malathion can suppress the synthesis of IL-2, IFN-γ, IL-4 and granzyme-B whereas chlorpyrifos is able to decrease the production of IL-6 in splenic lymphocytes. (Ibrahim, 2014) . In a recent study, acute intoxication of malathion (0.5 LD 50 ) resulted in reduced function of Th1 lymphocytes, DTH reaction and production of IFN-γ in random-bred albino rats. Monocrotophos suppresses DTH reaction, lymphocyte count and lymphocyte stimulation in sheep (Khurana and Chauhan, 2003) . Low dose oral exposure to acephate can modulate humoral immune response and DTH response to SRBCs in rodents (Sankhala et al., 2012) .

J o u r n a l P r e -p r o o f

There is small but evolving body of literature that advocates OP-induced autoimmune responses leading to several chronic manifestations. Systemic autoimmunity is measured by anti-nuclear antibodies. OP insecticide diazinon has been positively associated with serum antinuclear antigens in occupationally exposed male farmers (Parks et al., 2019) . In another finding, farmers having experience of long-term exposure to diazinon, fenitrothion, methidathion, malathion, chlorpyrifos, parathion, and profenofos had elevated level of blood antinuclear antibody.

Rheumatoid arthritis (RA) is a systemic autoimmune inflammatory disease. Its incidence of occurrence was higher in fonofos applicators (Meyer et al., 2017) . Koureas et al. (2017) conducted a cross sectional study among pesticide sprayers dealing with chlorpyriphos, phosmet and dimethoate in Thessaly (Greece). Multinomial analysis revealed that, frequencies for RA and allergic rhinitis were significantly higher in OP pesticide sprayers compared to control group.

Rheumatoid factor (RF) is the autoantibody that targets healthy tissues in the body. Rodgers (1997) has reported that, malathion administration at non-cholinergical doses can potentially increase serum RF and anti-dsDNA antibodies. Moreover, it can exacerbate progression of systemic lupus erythematosus which is an autoimmune disease with diverse clinical and immunological manifestations. Long-term exposure to dichlorvos can promote development of autoimmune hepatitis (Zhao et al., 2015) . Thus, OP compounds have certain implications for autoimmunity and organ damage.

People with under-performing immune system may be at high-risk of receiving SARS-CoV-2

infection. They may also remain infectious for a longer duration than others. Numerous studies targeted by OP compounds to hinder the activity of killer cells (Li, 2007) . OPs injure dendrites of DCs more likely through inhibition of protein kinases such as Akt family or ERK which are essential for cell proliferation and survival (Schäfer et al., 2013) . Pro-oxidative impact is exerted via Cytochrome-p450 based ROS production. ROS can overwhelm the cellular antioxidant status to manifest OS-a major trigger to necroptosis, pyroptosis, and parthanatos in immunocytes (Robinson et al., 2019) . Alongside, ROS-mediated disruption of mitochondrial-membrane exposes cardiolipin and mtDNA to cytosol thus provoking NLRP3 to compose inflammasome (Iyer et al., 2013) . C-reactive proteins are elevated following OP exposure and higher levels of this inflammatory marker can contribute to immunosuppression (Yoshida et al., 2020; Taghavian et al., 2016) . IFN constitutes the first line of defense against viral infections (Ivashkiv & Donlin, 2014 (Iyer et al., 2017) . Virions unable to escape IFN-response, usually fail J o u r n a l P r e -p r o o f to replicate in host (Iyer et al., 2017) . OP promotes IFN-depletion (Singh et al., 2013) and therefore can rupture the protective-shield against viral-attack.

Similar to OPs, SARS-CoV-2 can be detrimental to immune machinery and convergence of both can worsen the outcome of COVID-19. Virions utilize ACE-2 receptors to invade target cells.

However, certain essential oils like geranium and lemon strongly reduces expression of ACE-2 in epithelial cells that can subvert viral invasion (Senthil Kumar et al., 2020) . patients. Thus, onset of SARS-CoV-2 mediated auto-immune responses is confirmatory in these patients.

In summary, OP compounds are immunotoxic since they promotes apoptosis of immunocytes, lower immunoglobulin titer and autoimmune responses in organisms. Similar to OPs, SARS-CoV-2 targets immune system by modulating IFN response, lymphocyte count, cytokine homeostasis and autoimmune reaction. Hence, it is not unreasonable to claim that, co-exposure to both of the agents during the existing pandemic milieu could have altered the disease outcome of patients with COVID-19.

Striking similarities between pathological outcome of SARS-CoV-2 and OP-exposure can be Thus, above findings unequivocally suggest that, additional exposure to OPs can obviously intensify inflammation, respiratory-troubles and even casualties in patients with COVID-19 (Fig.   3 ).

In addition to immunotoxicity, OPs can promote other toxicities by injuring cardiovascular, hepatic as well as renal system of the body. The cardiotoxic effects of OP compounds have been reported in human as well as animal models following acute or chronic exposure (Georgiadis et al., 2018) . For instance, accidental exposure to phorate has been reported to provoke sinus were also evident (Kharoub and Elsharkawy, 2008; Ludomirsky et al., 1982 

Intriguingly subchronic exposure to methidathion and dimethoate insisted mononuclear cell infiltration in portal areas, sinusoidal dilatation, focal micro-vesicular steatosis and parenchymal degenerations (Gokalp et al., 2003; Sayim, 2007) . Besides, hepatomegaly is also evident following OP exposure. There is strong evidence regarding the impacts of OPs on biochemical parameters which are the markers of liver injury. The most common serum biomarkers of liver damage are aspartate transaminase (AST) and alanine transaminase (ALT). Studies have reported that, these markers are increased in response to wide spectrum of OPs such as dimethoate, monocrotophos, methyl parathion, dichlorvos, fenitrothion, omethoate, chlorpyrifos, diazinon and methidathion (Saafi et al., 2011; Goel et al., 2005; Beydilli et al., 2015; Gomes et al., 1999) .

Therefore, liver injury and some time mortality is obvious following OP exposure and may result from induction of OS (Sethi and Behera, 2016; Lukaszewicz-Hussain, 2013) .

It has been widely accepted that, exposure to OPs has a deleterious impact on the renal tissue and subsequently on the renal function of organisms. A recent study by Kaya et al., 2018 has revealed that, fenthion induces degeneration, vacuolization and atrophy in tubular epithelium of rats. Likewise, exposure to methidathion disrupts nephrotic architecture and promotes kidney injury (Sulak et al., 2005) . Bidrin is an OP insecticide formulation that triggers ROS-mediated tubular cytotoxicity by inducing lipid peroxidation in renal epithelial cells (Poovala et al., 1999) .

OP-induced nephrotoxicity has also been reported in human subjects. For instance, in an OPpoisoning case, a 17-year-old patient developed acute kidney injury followed by renal failure, 

Studies around the globe have confirmed the immunoprotective-potential of certain antioxidants against OP-mediated immunotoxicity (Table 4) . Ahmed et al. (2009) . Curcumin restores the proliferation of blood-lymphocytes exposed to parathion (Neeraj et al., 2014) . Sodhi et al. (2006) have documented that, vitamin E and selenium could be helpful to counteract malathion-induced decrement in total immunoglobulins and circulatory immune complexes. Walnut polyphenol normalizes splenic T lymphocyte proliferation following fenitrothion exposure. Moreover, it also helps to optimize T-cell related cytokines viz. Il-2, IL-4 and IFN-γ following fenitrothion-insult (Liu et al., 2018) . Propolis is a natural product derived from bees and harbors antioxidant property. It is evident that, propolis can ameliorate chlorpyrifos and profenos-mediated immune suppression by up-regulating immunoglobulin titer (Hamza et al., 2013) . Ascorbic-acid helps to maintain optimum levels of lysozyme-peroxidase, white blood-cells and serum-IgM in dimethoate-exposed Clarias batrachus (Narra, 2017) .

Interestingly, L-ascorbic acid reduces acephate-induced mortality of phagocytes in Drosophila melanogaster (Rajak et al., 2017) . Immunosuppressive impacts of malathion like subnormallevels of immunoglobulins and circulatory immune-complexes in chicks were partially ameliorated following supplementary-intake of Vitamin-E and Selenium (Sodhi et al., 2006) . Coadministration of green-tea extract is effective in ameliorating ethephon-induced immunotoxicity in mice (Abou-Zeid et al., 2018) . Exposure to diazinon reduces relative lymphocyte and monocyte counts, immunoglobulin concentration, hemagglutination titer and phagocytic index of lymphocytes. These immunotoxic impacts of diazinon are reversed upon co-administration of hesperidin in rats (Hassouna et al., 2015) . In addition to hesperidin, thymoquinone rescues from diazinon-mediated immunotoxicity by modulating cytokine levels (Danaei and Karami, 2017).

Zinc Oxide (ZnO) nanoparticles can efficiently scavenge free radicals and therefore reduce OS.

Aside, ZnO nanoparticles restore macrophage and serum lysozyme activities and cytokine levels that might be disrupted following chlorpyrifos exposure in rats (Essa et al., 2019) .

Therefore, consideration of these antioxidants in diets would be beneficial to sustain a healthy immune system under OP-exposure.

Evidences cited in the review confirm that, OPs disturb various components of immunemachinery that can be opportunistic for viral infections. Moreover, several respiratory difficulties including allergic-asthma, pneumonitis and chronic-bronchitis are positively correlated with OPexposure. Further, a healthy immune-system is essential to overcome SARS-CoV-2 infection.

Hence, pre-exposure to OPs or co-exposure to both deleterious agents might augment inflammatory-reactions, pyroptosis and pulmonary shortcomings coupled with higher fatal J o u r n a l P r e -p r o o f outcome in COVID-19 patients. OP-induced oxidative stress is the major driver of apoptosis in lymphoid-organs involved in maturation of lymphocytes and development of antibodies of highaffinity against viral antigens. Therefore, OP-mediated apoptotic lesions in lymphoid-tissues may also dampen the efficacy of potent vaccines to some extent.

Since direct experimental works dissecting the collaborative impacts of OPs and SARS-CoV-2 are still lacking, this review will attract the scientific community across the planet to concentrate on the proposed hypothesis to unveil the synergism between the two threats of human-race.

Serious health problems discussed in the review will also draw attention of global environment policy makers and concerned government/nongovernment organizations towards the perilous impacts of OP-exposure in human. Alongside, it will insist them to adopt necessary resolutions and amend policies that could limit human contacts with OPs.

Finally, it is important to note that, antioxidants may rescue immune system from detrimental impacts of OP compounds and hence diet rich in antioxidants would be helpful to maintain a good immune system that is essential to overcome COVID-19. Immunol. 20, 408. https://doi.org/10.1038/s41577-020-0360-z.

J o u r n a l P r e -p r o o f compounds downregulate angiotensin-converting enzyme 2 (ace2), a sars-cov-2 spike receptor-binding domain, in epithelial cells. Plants (Basel), 9(6), 770. Fig. 1 . Putative immunotoxic mechanism of SARS-CoV-2 and OPs at sub-cellular moiety.

SARS-CoV-2 invades host cell via S1/ACE-2 interaction and replicates using replication transcription complex (RCT) within the cytosolic moiety. S1 of spike protein or viral ds/sRNA bind with respective cell surface or endosomal Toll-like receptor (TLR) to fuel downstream signaling cascades involved in activation of NF-kB and synthesis of proinflammatory cytokines. Pathogen associated molecular patterns (PAMPs) and damage J o u r n a l P r e -p r o o f SARS-CoV-2 infection produces multiple respiratory troubles namely pneumonitis, acute respiratory distress syndrome (ARDS) and acute bronchitis in patients. In addition subnormal immune status increases the risk for septic shock and secondary infections. Multi-organ failure (cardiac, gastrointestinal, kidney, hepatic, neurological, olfactory, gustatory, ocular & cutaneous) is evident in certain cases. OP-induced necroinflammation at broncho-alveolar sites is the mediator of pulmonary diseases like pneumonitis, emphysema, ARDS, Chronic obstructive pulmonary disease (COPD), bronchitis, asthma and rhinitis. In addition, cellular death in lymphoid tissues promotes immunosuppression. Multi-organ injuries (neural, cardiac, renal, gastrointestinal & retinal) are also reported following OP-exposure. Therefore, OP contamination can intensify health predicaments to several folds and modulate disease outcome in patients with COVID-19.

J o u r n a l P r e -p r o o f 

Oxidative damage, hyperlipidemia and histological alterations of cardiac and skeletal muscles induced by different doses of diazinon in female rats

Organophosphorus ester-induced chronic neurotoxicity

Ameliorating effects of green tea on ethephon-induced immunotoxicity and oxidative stress in mice

Dysregulation of type I interferon responses in COVID-19

Immune modulating effects of malathion with the role of bradykinin potentiating factor in juvenile male rats

Assessment of phosphamidon-induced apoptosis in human peripheral blood mononuclear cells: protective effects of N-acetylcysteine and curcumin

Role of HSP27 and reduced glutathione in modulating malathion-induced apoptosis of human peripheral blood mononuclear cells: ameliorating effect of N-acetylcysteine and curcumin

Inhibition of human bone marrow-derived stem cell colony formation (CFU-E, BFU-E, and CFU-GM) following in vitro exposure to organophosphates

Highly pathogenic coronavirus N protein aggravates lung injury by MASP-2-mediated complement over-activation

Haemato-biochemical and immunopathophysiological effects of chronic toxicity with synthetic pyrethroid, organophosphate and chlorinated pesticides in broiler chicks

Lupus anticoagulant and mortality in patients hospitalized for COVID-19

Pesticides and cardiotoxicity. Where do we stand?

Self-reported olfactory and taste disorders in SARS-CoV-2 patients: a cross-sectional study

Simultaneous administration of hesperidin or garlic oil modulates diazinon-induced hematoand immunotoxicity in rats

Immunotoxicity of the organochlorine pesticide methoxychlor in female ICR, BALB/c, and C3H/He mice

Modulation of macrophage functionality induced in vitro by chlorpyrifos and carbendazim pesticides

CD147 as a Target for COVID-19 Treatment: Suggested Effects of Azithromycin and Stem Cell Engagement. Stem

Neutrophil function and infectious disease in workers occupationally exposed to phosphoorganic pesticides: Role of mononuclear-derived chemotactic factor for neutrophils

SARS-CoV-2 cell entry depends on ACE2 and TMPRSS2 and is blocked by a clinically proven protease inhibitor

Pesticide use and adult-onset asthma among male farmers in the Agricultural Health Study

Clinical features of patients infected with 2019 novel coronavirus in Wuhan

Immunotoxicity of sub-chronic doses of diazinon in male albino Wister rats

Subchronic dichlorvos-induced Cardiotoxicity in Wistar rats: Mitigative efficacy of Nigella sativa oil

Regulation of type I interferon responses

interferons is a major determinant of HIV-1 transmission fitness

Mitochondrial cardiolipin is required for Nlrp3 inflammasome activation

New perspectives for mucolytic, antiinflammatory and adjunctive therapy with 1,8-cineole in COPD and asthma: review on the new therapeutic approach

CYP/PON genetic variations as determinant of

Acute renal involvement in organophosphate poisoning: histological and immunochemical investigations

mardiotoxicity of acute organophosphate poisoning

Immunopathological effects of monocrotophos on humoral immune response in sheep

Increased frequency of rheumatoid arthritis and allergic rhinitis among pesticide sprayers and associations with pesticide use

Cardiovascular Effects of Acute Organophosphate Poisoning. Asia Pac

Organophosphate poisoning and subsequent acute kidney injury risk: a nationwide population-based cohort study

Nuclear NF-κB contributes to chlorpyrifos-induced apoptosis through p53 signaling in human neural precursor cells

Coronavirus infections and immune responses

New Mechanism of Organophosphorus Pesticide-induced Immunotoxicity

The by-products generated during sarin synthesis in the Tokyo sarin disaster induced inhibition of natural killer and cytotoxic T lymphocyte activity

Vitro Immunotoxicity of

lymphocytes and its relation to GSTM1 and GSTT1 polymorphism

Evaluation of immunotoxicity induced by diazinon in C57bl/6 mice

A structural analysis of M protein in coronavirus assembly and morphology

Detection of SARS-CoV-2-Specific Humoral and Cellular Immunity in COVID-19 Convalescent Individuals

Severe acute respiratory syndrome coronavirus envelope protein ion channel activity promotes virus fitness and pathogenesis

Influence of chlorpyrifos on the profile of subpopulations of immunoactive cells and their phagocytic activity in an experimental in vivo model

Lifetime pesticide use and antinuclear antibodies in male farmers from the agricultural health study

Racial disparities in COVID-19 mortality across Michigan, United States

Biochemical effects of various pesticides on sprayers of grape gardens

Clinical features of organophosphate poisoning: A review of different classification systems and approaches

Role of reactive oxygen metabolites in organophosphate-bidrin-induced renal tubular cytotoxicity

Neutrophil function in workers exposed to organophosphate and carbamate insecticides

Exploring hazards of acute exposure of Acephate in Drosophila melanogaster and search for l-ascorbic acid mediated defense in it

Chronic exposure to acephate triggers ROS-mediated injuries at organismal and sub-organismal levels of Drosophila melanogaster

Aged garlic extract ameliorates immunotoxicity, hematotoxicity and impaired burn-healing in malathion-and carbaryltreated male albino rats

Cutaneous manifestations in COVID-19: a first perspective

Serum immunoglobulins (IgA, IgM, IgE) and acetylcholinesterase level determination in agricultural spray workers exposed to organophosphates pesticides in district Gujranwala

Programmed necrotic cell death of macrophages: Focus on pyroptosis, necroptosis, and parthanatos

Effect of Administration of Malathion for 14 Days on

Effects of oral administration of malathion on the course of disease in MRL-lpr mice

Organophosphate pesticide exposure and neurobehavioral performance in agricultural and non-agricultural Hispanic workers

Protective effect of date palm fruit extract (Phoenix dactylifera L.) on dimethoate inducedoxidative stress in rat liver

Organochlorine and organophosphorus pesticide residues in breast milk from Bhopal

Hematological and immunological changes due to short-term oral administration of acephate

Dimethoate-induced biochemical and histopathological changes in the liver of rats

Influence of organophosphate poisoning on human dendritic cells

Neurotoxic effects of organophosphate insecticides: an intermediate syndrome

Acute liver failure due to organophosphorous

Immunopathologic effects of oral administration of chlorpyrifos in broiler chicks

Cell entry mechanisms of SARS-CoV-2

Jensenone from eucalyptus essential oil as a potential inhibitor of COVID 19 corona virus infection

Triazophos induced oxidative stress and histomorphological changes in liver and kidney of female albino rats. Pestic

Association of cardiac injury with mortality in hospitalized patients with COVID-19 in Wuhan

Assessment of cardiotoxicity and effects of malathion on the early development of zebrafish (Danio rerio) using computer vision for heart rate quantification

Lipopolysaccharide (LPS) induced activation of the immune system in control rats and rats chronically exposed to a low level of the organothiophosphate insecticide, acephate

Pre-natal/juvenile chlorpyrifos exposure associated with immunotoxicity in adulthood in Swiss albino mice

A protective effect of vitamin E and selenium in ameliorating the immunotoxicity of malathion in chicks

Evaluation of immunotoxicity and oxidative stress due to in vitro exposure of Dimethoate in chicken lymphocytes

Levels of select organophosphates in human colostrum and mature milk samples in rural region of Faizabad district

Immunological parameters in humans exposed to pesticides in the agricultural environment

Immunotoxicity of phosphamidon following subchronic exposure in albino rats

Ameliorative effect of nanoencapsulated flavonoid against chlorpyrifos-induced hepatic oxidative damage and immunotoxicity in Wistar rats

Nephrotoxicity in rats induced by organophosphate insecticide methidathion and ameliorating effects of vitamins E and C. Pestic

Comparative toxicological study between exposed and non-exposed farmers to organophosphorus pesticides

In vivo immunosuppression by synthetic pyrethroid (cypermethrin) pesticide in mice and goats

Lymphopenia predicts disease severity of COVID-19: a descriptive and predictive study

its clinical significance

Structural basis for translational shutdown and immune evasion by the Nsp1 protein of SARS-CoV-2

Immunologic Abnormalities in Humans Exposed to Chlorpyrifos: Preliminary Observations

Immunological abnormalities in humans chronically exposed to chlorpyrifos

Studies on the Action of Dimethoate on the Immune System

Simultaneous geno-and immunotoxicological investigations for early detection of organophosphate toxicity in rats

Chronic bronchitis among nonsmoking farm women in the agricultural health study

Malathion increases apoptotic cell death by inducing lysosomal membrane permeabilization in N2a neuroblastoma cells: a J o u r n a l P r e -p r o o f model for neurodegeneration in Alzheimer's disease

Early onset pneumonia in patients with cholinesterase inhibitor poisoning

The laboratory tests and host immunity

C-reactive protein levels in the early stage of COVID-19

World Health Organization, 2020a. Statement on the Second Meeting of the International Health Regulations (2005) Emergency Committee regarding the outbreak of novel

the-second-meeting-of-the-international-health-regulations-(2005)-emergency-committeeregarding-the-outbreak-of-novel-coronavirus-(2019-ncov) (accessed 28th

Virtual press conference on COVID-19-11

Cryo-EM structure of the 2019-nCoV spike in the prefusion J o u r n a l P r e -p r o o f conformation

Fusion mechanism of 2019-nCoV and fusion inhibitors targeting HR1 domain in spike protein

Transcriptomic characteristics of bronchoalveolar lavage fluid and peripheral blood mononuclear cells in COVID-19 patients

Methoxychlor enhances degranulation of murine mast cells by regulating FcϵRI-mediated signal transduction

Cardiotoxicity in rats induced by methidathion and ameliorating effect of vitamins E and C

C reactive protein impairs adaptive immunity in immune cells of patients with melanoma

SARS-CoV-2 nsp13, nsp14, nsp15 and orf6 function as potent interferon antagonists

The effect of chronic intoxication by organophosphate insecticides on the parameters of innate and adaptive immunity and realization of the cholinergic antiinflammatory pathway

The Types of Dysfunction of Th1, Th2 Lymphocytes After Various Toxic Chemicals Acute Intoxication

Acute Renal Failure due to Organophosphate Poisoning: A Case Report

Cardiotoxicity in rabbits after a low-level exposure to diazinon, propoxur, and chlorpyrifos

Neurobehavioral, biochemical and immunological manifestations in workers exposed to organophosphate insecticides

Occupational and environmental risk factors for respiratory symptoms in rural Beijing, China

Profile of natural anticoagulant, coagulant factor and anti-phospholipid antibody in critically ill COVID-19 patients

The ORF8 protein of SARS-CoV-2 mediates immune evasion through potently downregulating MHC-I. bioRxiv

Dichlorvos induced autoimmune hepatitis: a case report and review of literature

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) membrane (M) protein inhibits type I and III interferon production by targeting RIG-I/MDA-5 signaling. bioRxiv

A pneumonia outbreak associated with a new coronavirus of probable bat origin

Acute SARS-CoV-2 Infection Impairs Dendritic Cell and T Cell Responses

Pathogenic T cells and inflammatory monocytes incite inflammatory storm in severe COVID-19 patients

pathways to dwarf interferon (IFN)-mediated anti-viral immune response

M-protein blocks mitochondrial antiviral-signaling protein (MAVS)-dependent activation of kinases to down-regulate IFN production. NSP1 also degrades various host mRNAs, some of them may be crucial for immune reaction against SARS-CoV-2

Being lipophilic in nature, OP crosses cell membrane and passes through phase-I detoxification machinery to generate massive reactive oxygen species (ROS)

ROS inhibits phosphatases to enhance production of pro-inflammatory cytokines. ROS also stabilizes hypoxia-inducible factor 1-alpha (HIF-1α) by oxidizing prolyl-hydroxylase (PHD) to transcribe vascular endothelial growth factor (VEGF) involved in airway-inflammation, airway-hyperresponsiveness and lymphocyte-dysfunction. ROS-induced lipid peroxidation, proteindegradation and DNA-damage simultaneously trigger necroinflammation. OP activates suppressor of cytokine signaling-3 (SOCS3) to disrupt JAK/STAT mediated anti-viral immune response. Disruption of mitochondrial boundary is promoted by apoptosis-signal-regulatingkinase-1 (ASK-1) which remains inactive as long as it is bound to thioredoxin

P r e -p r o o f attracts neutrophil (NT) extravasation, degranulation of cytosolic-contents (HBP, elastase, cathepsins, azurocidin, collagenase, gelatinase)

Macrophages present viral antigens to naive-T-cells of mucosa-associated-lymphoid-tissues

Activated naive-T-cells differentiate into CTL and T H 17 to exaggerated inflammation and cytotoxicity

OP-induced ROS and subsequent oxidative-stress triggers multiple apoptotic cascades to scrape lung-epithelium. Shedding of damaged cells disrupts epithelial-barrier. Alongside, OP insists degranulation of mast cells (MCs) to release histamine

These events reduce the alveolar-volume interfering with O 2 absorption. Additionally, OP-contamination invites infiltration of neutrophil and eosinophil (ES) to exert necroinflammation. OP inhibits M2-receptor in brain leading to elevated levels of acetylcholine (ACh)

Highlights • SARS-CoV-2 is a highly contagious retrovirus causing COVID-19

• Virions trigger cytokine-storm leading to necroinflammation & respiratory ailments. • Overuse of organophosphates (OPs) contaminates drinking water & food-products

• OPs fuel oxidative stress, immunotoxicity, inflammation & lung pathology. • Co-exposure circumstances can invite severe health troubles in COVID-19 patients

Increased reactive oxygen species (ROS) and lipid peroxidation in lymphocytes; higher DNA damage; decreased lymphocyte viability; reduced cell proliferation and apoptosis in splenocytes; reduced activity of macrophage lysosomal enzyme and increased production of IL-1β, TNFα and nitric oxide. Olakkaran et al., 2020; Helali et al., 2016; Battaglia et al., 2010 OP flame retardants: Triphenyl phosphate, Tris (1,3dichloropropan-2-yl) phosphate, Tributyl phosphate, Tris (2methylphenyl) phosphate, Tris (2-chloroethyl) phosphate, Tris (2-butoxyethyl) phosphate Human monocytic leukemia cell line Reduced cell viability and adhesion property; reduced production of anti-inflammatory cytokines (IL-10 and IL-13) and increased production of proinflammatory cytokines (TNF-α). MethoxychlorMurine mast cells Increased degranulation of mast cells via induction of F cε RI-mediated signal transduction. Tang et al., 2003 J o u r n a l P r e -p r o o f J o u r n a l P r e -p r o o f Hermanowicz & Kossman, 1984 J o u r n a l P r e -p r o o f Green tea extract (2 g of tea leaves/100mL; 2 months) normalized lymphocyte count; improved humoral immune response and delayed type hypersensitivity reaction; partially ameliorated phagocytic acidity of neutrophils.J o u r n a l P r e -p r o o f

☐ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.