key: cord-0973023-zvvacf65
authors: Coperchini, Francesca; Chiovato, Luca; Ricci, Gianluca; Croce, Laura; Magri, Flavia; Rotondi, Mario
title: The Cytokine storm in COVID-19: Further advances in our understanding the role of specific chemokines involved
date: 2021-01-08
journal: Cytokine Growth Factor Rev
DOI: 10.1016/j.cytogfr.2020.12.005
sha: 4a4edf1ed00c39c27ddfdc76acf0f2c77e4d0fc0
doc_id: 973023
cord_uid: zvvacf65

SARS-COV-2 infection represents the greatest pandemic of the world, counting daily increasing number of subjects positive to the virus and, sadly, increasing number of deaths. Current studies reported that the cytokine/chemokine network is crucial in the onset and maintenance of the “cytokine storm”, the event occurring in those patients in whom the progression of COVID-19 will progress, in most cases, to a very severe and potentially threatening disease. Detecting a possible “immune signature” in patients, as assessed by chemokines status in patients with COVID-19, could be helpful for individual risk stratification for developing a more or less severe clinical course of the disease. The present review is specifically aimed at overviewing current evidences provided by in vitro and in vivo studies addressing the issue of which chemokines seems to be involved, at least at present, in COVID-19. Currently available experimental and clinical studies regarding those chemokines more deeply studied in COVID-19, with a specific focus on their role in the cytokine storm and ultimately with their ability to predict the clinical course of the disease, will be taken into account. Moreover, similarities and differences between chemokines and cytokines, which both contribute to the onset of the pro-inflammatory loop characterizing SARS-COV-2 infection, will be briefly discussed. Future studies will rapidly accumulate in the next months and their results will hopefully provide more insights as to the complex physiopathology of COVID-19-related cytokine storm. This will likely make the present review somehow “dated” in a short time, but still the present review provides an overview of the scenario of the current knowledge on this topic.

significant upregulation of chemokines (CCL2, CXCL5, and CXCL6), in samples from patients as compared to samples from healthy control [11] . This finding was also confirmed in SARS-CoV-2-infected pancreatic endocrine cells compared to mock infected cells. Taken together the above results, it was consistently reported that many chemokines are involved in COVID-19 potentially influencing its progression and risk of mortality [11] [12] [13] . However, only few of these chemokines were object of studies specifically aimed at a better characterization of their role and at providing an explanation of their possible clinical utility in the management of the disease. In particular, there were 9 chemokines which, according to current knowledge, seem to play a role in SARS-COV-2 infection. Here follows a description of the more recent evidence of the involvement of each chemokine in COVID-19.

For the purpose of the present review, we followed in the subsequent paragraphs a "family order", in that, starting from CXC family of chemokines, each chemokine was listed in ascending numerical order. In order to show a rapid link between a given chemokine and the studies evaluating it, Table 1 was provided. In particular, chemokines less deeply investigated (single study and/or evaluated within a wide panel of other chemokines) as well as those chemokines for which more data are available are listed in Table 1 .

In order to facilitate reading, all chemokines will be listed in the heading of the paragraph with both old and new nomenclature, while only the new nomenclature will be used along the text. For clarity purpose, data from in vitro studies will anticipate those obtained by in vivo studies, unless specifically requested. In particular, since most studies evaluated more than one chemokine, the results will be reported with more details in the sub-paragraph of the specific chemokine that was found to be either more extensively evaluated or more relevant. All studies evaluating a specific chemokine are listed in Table 1 , also including those chemokines less deeply investigated (single study and/or evaluated within a wide panel of other chemokines). CXCL1 binds to the G-protein coupled receptor, CXC receptor 2, and it is considered to be a signalling growth factor [14, 15] . CXCL1 is a known chemoattractant for neutrophils, playing a role in the inflammatory process. An abnormal expression and secretion of this chemokine is also associated with the growth and progression of some types of tumours [14] . There are few literature data regarding the role of this chemokine in SARS-COV-2 infection. This chemokine was identified, among others, to be the one of the more abundantly expressed by macrophages involved in SARS-COV2 infection, especially in more severe cases [8] . In addition, in vitro evidences, obtained in an established model of lung fibrosis induced by SARS-COV-2, demonstrated that the reduction of CXCL1 and other inflammatory markers in the lung by the peptide RP-832c would parallel the reduction of lung fibrosis [16] .

CXCL8 is a member of the CXC chemokine family commonly referred to as interleukin-8 according to the old nomenclature. CXCL8 is secreted by mononuclear macrophages, neutrophils, eosinophils, T lymphocytes, epithelial cells, and fibroblasts. It functions as a chemotactic factor by recruiting neutrophils to the site of infection. CXCL8 was indeed the first chemokine identified.

More recently, CXCL8 became increasingly studied in different types of human cancer owing to its well established pro-tumorigenic effects [17, 18] . CXCL8 seems to play an important role also in COVID-19 disease. In vitro evidence, by RNA-Seq data from human bronchial airway epithelial cells, showed that SARS-CoV-2 infection upregulates the production CXCL8 and other factors from both the apical and basolateral cell surface [19] . Moving to in vivo results, a retrospective study performed on demographic data, epidemiological history, clinical manifestations, and J o u r n a l P r e -p r o o f laboratory findings of patients with COVID-19, demonstrated that, together with other inflammatory molecules, the circulating levels of CXCL8 were significantly higher in patients bearing a more severe disease as compared to those with milder clinical symptoms [20] . These data suggested a positive correlation between CXCL8 levels and the degree of COVID-19 severity.

Further support to this concept stems from a study on 69 patients with COVID-19 showing that serum CXCL8 (and IL-6) levels were, among a panel of other cytokines, remarkably higher in the severe group compared with the non-severe group. In particular, high CXCL8 levels persisted until hospital day-5, being associated with disease progression [21] . The Authors, suggested that, the neutrophilia, frequently occurring in severe COVID-19, might be ascribed to the abnormal elevation of CXCL8 and granulocyte-macrophage colony-stimulating factor [21, 22] . In a subsequent study, a direct comparison between patients with severe versus moderate disease found that higher levels of inflammatory chemokines including MCP-1/CCL2, IP-10/CXCL10, IL-8/CXCL8, are found in patients with critical illness, correlating with both neutrophilia and increased circulating proinflammatory CD14+ CD16++ monocytes [23] .

Moreover, Diorio et al, found an increase in markers of endothelial dysfunction in both children affected by Multisystem inflammatory syndrome (MIS-C) or severe COVID-19. Indeed elevated sC5b-9 (a marker of endothelial dysfunction) correlated with increased CXCL8 (as well as IL-6 and TNF-α) levels, suggesting a link between CXCL8 levels and innate immunity dysfunction commonly observed in these patients [24] . In addition, elevated serum concentrations of CXCL8 (together with other factors) at admission were also found to be strong and independent predictors of survival in hospitalized patients with COVID-19 [25] .

Finally, it seems worth remembering that BMS-986253, a monoclonal antibody inhibiting CXCL8, previously tested in a Phase I clinical trial on cancer patients [26] is currently object of an ongoing Phase 2 clinical trial in patients affected by severe COVID-19 (NCT04347226).

J o u r n a l P r e -p r o o f CXCL9 (C-X-C Motif Chemokine Ligand 9) is a CXC chemokine with chemoattractant activity for lymphocytes but not for neutrophils binding to C-X-C motif chemokine 3. This chemokine is involved in several inflammatory processes being (as CXCL10) chemoattractant for immune system cells of Th-1 phenotype [27, 28] . This chemokine was found to be involved in COVID-19 disease being positively correlated to the age of the patients. Moratto et al., measured a panel of chemokines in plasma samples from 14 children and 9 adults with COVID-19 and in respective age-matched control groups. Briefly, adult patients with COVID-19 displayed higher levels of CXCL9 than children with COVID-19, while overlapping CXCL9 concentrations were observed between adult and children control subjects. Interestingly enough, the adults involved in the study also displayed a prominent Th1 polarization of immune response against SARS-CoV2 suggesting that prolonged T cell activation in adults with COVID-19 might result in Th1 polarization and possibly in pulmonary tissue damage by activated T cells [29] .

Of note, this age-dependent difference was not observed for plasma levels of other chemokines including CCL5, CXCL10, CCL2, and CXCL8. Although of potential interest, the clinical significance of this age-related behaviour, remains at present yet to be fully elucidated.

CXCL10 belongs to the CXC family of chemokines containing a single and variable amino acid between the two first of four highly conserved cysteine residues. This chemokine binds to CXCR3 receptor through which it exerts multiple functions [30] . CXCL10 is secreted after induction by IFN-γ by a wide variety of human cell types including immune cells and resident cells. High level of CXCL10 in peripheral fluids represent a marker of host immune response, specifically of Th1 orientated T-cells [31] . CXCL10 is at present the most studied chemokine within SARS-COV-2 infection, being consistently identified by several studies as the chemokine playing the major role in the SARS-COV-2-induced cytokine storm [10] . Indeed, the presence of elevated levels of CXCL10 J o u r n a l P r e -p r o o f were strongly related with the infiltration of immune cells into alveolar space, peribronchial, and perivascular of the lung [4] . Interestingly, circulating CXCL10 levels were found to be increased in those patients with a more severe clinical course of both COVID-19 as well as of the previous MERS-CoV infection [4] .

Yang et al, recently highlighted that CXCL10 levels measured at different time points in COVID-19 patients (i.e. 7 days after diagnosis, between 8 and 14 days and during the recovery phase starting from 15 days after disease onset) were positively correlated with increasing severity (critically ill> severe> moderate) of COVID 19 disease. Furthermore, the circulating levels of CXCL10 were elevated upon admission and remained high during the phase of disease progression. This observation appears of not negligible clinical relevance in that, it would suggest that serum CXCL10 could be also considered a marker for predicting disease progression [32] . In addition, Zhang et al., reported a CXCL10 (and CCL2) positive signature in a significantly higher proportion of macrophages derived from severe COVID-19 than in the other inflamed tissues [33] . More importantly, the Authors, concluded that IFN-γ by activation of CXCL10+ CCL2+ macrophage subset would act as a mediator of severe disease, suggesting that the anti-Type II IFN treatment, including JAK inhibitors, might prove effective for inhibiting the onset of cytokine storm [53, 54] .

New information were provided also by in a silico study, in which algorithm analysis of the gene set expression based on Core Gene CXCL10 (ssGSEA) showed that CXCL10 is highly expressed in SARS-COV-2 infected patients and that CD4 and CD8 cells are highly enriched in samples with higher expression of CXCL10. On the contrary, samples with low expression of CXCL10 appeared to be enriched in dendritic cells [34] . Moreover Chi et al, showed that, among a panel of chemokines, CXCL10 circulating levels were progressively increased according to a mild, moderate or severe course of COVID-19 [9] .

Hue et al, performed an interesting prospective mono-center observational study showing that serum concentrations of CXCL10 and nasopharyngeal viral loads were both positively associated J o u r n a l P r e -p r o o f with the outcomes of COVID-19 patients [35] . Indeed, there were dramatically lower serum concentrations of CXCL10 (and some other cytokines and chemokines) in patients having bacterial/non-documented ARDS than in patients with non-COVID-19 viral ARDS or COVID -19, suggesting that CXCL10 and the other chemokines could be biomarkers of viral infections.

Moreover, serum concentrations of CXCL10 as well as SARS-CoV-2 viral loads remained significantly higher in patients who died than in survivors [35] . Interestingly, they also identified a group of chemokines/cytokines, including CXCL10 that were associated with day-28 mortality in COVID-19 ARDS patients [55] . In a recent retrospective study, evaluating the circulating levels of several chemokine in 74 patients with severe and critical ill COVID-19, CXCL10 and CCL2 were identified as biomarkers positively associated with severity and death-risk of COVID-19. In particular, the circulating concentrations of both CXCL10 and CCL2 in critically ill patients were higher than those found in severe patients. No difference was found in the level of another chemokine (i.e CCL3). Interestingly, stratification of patients according to the d-dimer levels, revealed that the levels of both CXCL10 and CCL2 were higher in patients showing highest ddimer levels, suggesting that CXCL10 and CCL2 would be related to the risk of death in COVID-19 patients [36] .

Blot et al., in BALF from COVID-19 patients, found that, higher CXCL10 levels in both the systemic and alveolar compartments in those patients developing acute respiratory distress syndrome (ARDS) were associated with a longer duration of mechanical ventilation. This finding emphasizes the involvement of the CXCL10-CXCR3 signaling axis in the pathogenesis of severe forms of COVID-19 infection, thus representing a potential therapeutic target [37] . It seems worth remembering that, corticosteroids that showed beneficial effects in COVID-19 patients actually act, through inhibition of the Th1 pathway, upstream of CXCL10. The fact that corticosteroids may reduce CXCL10 secretion was already known [31 [38] . More specifically, Lev et al. reported that a significant decrease of CXCL10 levels was observed in COVID-19 patients receiving J o u r n a l P r e -p r o o f corticosteroids drugs [39] . If further validated, this finding might suggest potentially promising therapeutic approach by specifically neutralizing CXCL10.

CCL2 is the first discovered human chemokine belonging to the CC chemokine family [40] . CCL2 regulates immune cell recruitment to specific sites. CCL2 preferentially binds the CCR2 receptor, which is expressed in various tissues including blood, brain, heart, kidney, liver, lung, ovary, pancreas, spinal cord, spleen and thymus [41] . CCL2 is constitutively expressed for homeostatic functions such as regulating lymphocyte trafficking from blood to lymph nodes, while it is induced during inflammatory responses when leukocytes are required for tissue defense and repair [42, 43] . demonstrating that, significant differences in cell counts of lymphocytes, neutrophils, eosinophils were associated with a profoundly different chemokine profiles between the two groups. Moreover, the circulating levels of CCL2 were nearly doubled (264 vs. 134 pg/mL) in the severe group compared to non-severe group [21] . Also Huang et al., confirmed that intensive care unit (ICU) patients showed significantly higher plasma levels of GSCF, CXCL10, CCL2, CCL3, and TNF-α than those not requiring ICU, further indicating that the occurrence of the "cytokine storms" largely J o u r n a l P r e -p r o o f contributes in aggravating the disease, being also associated with the progression of pneumonia/respiratory failure [22] . As previously reported, CCL2 (together with CXCL10) was appear to be associated to disease severity in COVID-19 patients [36] . Higher CCL2 levels were also independently associated (together with other immune soluble biomarkers) with mortality in COVID-19 patients [44] . Kwon et al, confirmed that plasma concentrations of CCL2 (as well as of CXCL10, CXCL8 and CXCL9) were higher in patients with, severe or critical disease, compared with patients with mild disease but, only CCL2, among the cytokines/chemokines analyzed, was positively correlated with the viral load [45] . Finally, Sierra et al, isolated RNA from nasopharyngeal swab samples from COVID-19 positive patients, stratified in very symptomatic, complicated, and fatal cases, showing that CCL2 (and CCL3) expressions were significantly higher in patients with unfavorable outcome compared with cases with a favorable evolution or with negative controls. Moreover, CCL2 higher expression was associated with marked asthenia and with the presence of dyspnea in the unfavorable evolution group. More interestingly the "multivariate beta regression analysis showed that CCL2 was associated with a more severe outcome [46] .

CCL3 (C-C Motif Chemokine Ligand 3) is a chemokine binding the CCR1, CCR4 and CCR5 chemokine receptors. This chemokine is one of the major HIV-suppressive factors produced by CD8+ T-cells [47] . Recombinant CCL3 was demonstrated to induce a dose-dependent inhibition of different strains of HIV-1, HIV-2, and simian immunodeficiency virus (SIV). Interestingly, it was previously demonstrated that polymorphisms at CCL3 locus are associated with resistance or susceptibility to infection by human immunodeficiency virus type 1 [48] .

CCL3 should be included to the list of those chemokines found to be elevated in patients with a more severe prognosis of COVID-9 [5, 7, 8, 49] . It was reported that high levels of some chemokines and of CCL3 in particular, in view of their ability to recruit neutrophils and monocytes, J o u r n a l P r e -p r o o f characterize those children developing MISC as a consequence of SARS-COV-2 infection. This finding also suggests that autoreactivity secondary to SARS-CoV-2 infection and the inflammatory innate immune response may be critical in the pathogenesis of MIS-C [50] . CCL3 together with other chemokines was found to be highly expressed in PBMC and BALF of COVID-19 patients compared with controls [5] . The increased transcription of CCL2 and CCL3 chemokines receptors CCR2 (i.e. the CCL2 receptor) and CCR5 (i.e. the CCL3 receptor) observed would confirm the activation of the inflammatory signalling promoted by these chemokine/chemokine receptor binding (32) . In addition, in the previously cited study by Sierra et al, CCL3 RNA expression level was higher in COVID-19 patients with an unfavourable outcome compared with cases with a favourable evolution or with negative controls and was also associated with asthenia [46] . Of note, Chua et al, investigated the immune response in patients with COVID-19 by single-cell RNA sequencing (scRNA-seq) of nasopharyngeal and bronchial samples, with the aim of identifying specific chemokines/chemokine-receptors genes expression correlating with disease severity. They found a significant induction of CCL2 and CCL3 genes expression in macrophages together with an increased expression of the CCR1 (receptor for both chemokines) gene, in patients with critical COVID-19. The Authors concluded that targeting these chemokine/chemokine receptor binding might suppress immune hyper activation in critical COVID-19 patients [8] .

CCL5 is a chemokine of the CC chemokine family that binds to CCR1, CCR3, and mainly CCR5 receptors [51] . CCL5 plays an active role in recruiting a variety of leukocytes including T cells, macrophages, eosinophils, and basophils into inflammatory sites. In collaboration with cytokines such as IL-2 and IFN-γ that are released by T cells, CCL5 also induces the activation and proliferation of natural killer cells to generate CC chemokine-activated killer cells [52] . Moreover, it seems that the CCL5/CCR5 binding may favor tumor development by acting as growth factor, stimulating angiogenesis, modulating the extracellular matrix, inducing the recruitment of additional stromal and inflammatory cells, and taking part in tumor immune evasion [53] ., It was previously reported that, an increased level of CCL5 (together with other chemokines), could be observed after 24 and 48 hours, in mice infected with the previous SARS-CoV [54] . Similarly, the circulating levels of CCL5 seem to play a role also in SARS-COV-2 infection, , even if controversial data regarding CCL5 in SARS-COV-2 disease progression are present. Indeed, Li et al, analyzed a panel of blood cytokines in 69 patients with COVID-19, reporting a slight but significant increased CCL5 level, in patients with severe as compared to non-severe COVID-19 [21] . Hue et al, observed a positive correlation between higher CCL5 levels and severe COVID 19 manifestation, highlighting the important role of this chemokine in CS induced ARDS [35] . At difference, Zhao et al evaluated 71 COVID 19 patients, reporting that circulating CCL5 levels were significantly elevated only in mild cases (in whom they remained elevated for 3/4 week after recovery) as compared with healthy controls. Of note, no elevation of CCL5 circulating levels was observed in the severe group during disease progression, which prompted the Authors to suggest that CCL5 might play a protective role by preventing the development of severe illness in COVID-19 patients [55] . Interestingly enough, Takahashi et al, reported that, among a panel of 71 cytokines/chemokines, CCL5 circulating levels (together with CXCL8 and IL-18 levels) were higher in male compared to female patients affected by SARS-COV-2, suggesting the existence of a gender-dependent effect. Of note some clinical data suggest that treatment with the CCR5 blocking antibody (i.e. Leronlimab) could represent a promising immunotherapy strategy for COVID 19 treatment [56] . More specifically, Patterson et al, reported that treatment with Leronlimab lead to a complete CCR5 receptor occupancy on macrophage and T cells, rapid reduction of plasma IL-6, restoration of the CD4/CD8 ratio, and a significant decrease in SARS-COV-2 plasma viremia [57] .

Taking together the above evidences, the role of CCL5 in SARS-COV-2 disease definitely requires corroboration, but further advances in the comprehension of the role of CCL5 could be crucial for better understanding the immunological profile as well as the gender-related differences in the clinical course of SARS-COV-2.

CCL19 is a pro-inflammatory chemokine that belongs to the CC chemokine family. The binding of CCL19 to its receptor CCR7, mediates several migratory events in adaptive immunity following antigen encounter by immunocytes [58] .The binding of CCL19 to CCR7 receptor is crucial for the recruitment of antigen presenting dendritic cells and naïve T-cells to secondary lymphoid organs [59] . CCL19 also plays an important role in rheumatic and autoimmune diseases being overexpressed in autoimmune responses and in chronic inflammatory conditions [58] . Regarding the SARS-COV-2 infection scenario, there are limited data about the role of CCL19, of note Balnis et al. found that high levels of CCL19 chemokine in patients' serum significantly correlated with outcome and greater mortality in a cohort of patients on mechanical ventilation infected by SASR-COV2 developing ARDS. Based on this findings, the Authors suggested that CCL19 determination could facilitate early identification COVID19-ARDS patients at higher risk of death [60] .

CCL20 belongs to the subfamily of CC chemokines and binds to C-C chemokine receptor CCR6.

The binding of CCL20 to CCR6 is responsible for the chemotaxis of dendritic cells (DC), lymphocytes, effector/memory T-cells and B-cells and plays an important role at skin and mucosal surfaces in both homeostatic and inflammatory conditions [61] . CCL20 is also involved in cancer inflammation and autoimmune diseases [61] [62] [63] . CCL20 is involved in the recruitment of both the pro-inflammatory IL-17 producing helper T-cells (Th17) and the regulatory T-cells (Treg) to the sites of inflammation [61] . CCL20 together with other chemokines, was shown to be involved, in the pathogenesis of COVID-19, being expressed by immune activated macrophages in critical cases J o u r n a l P r e -p r o o f of SARS-COV2 infection and being found at higher levels in those patients requiring mechanic ventilation [8] . In addition, CCL20 (similarly to the above described CCL3) was found to be elevated in children affected by MISC as a consequence of SARS-COV-2 infection [50] . Hue et al, reported that CCL20 serum levels (together with other chemokines described in previous paragraphs), were higher in patients with viral ARDS and COVID-19 as compared to non-COVID-19 ARDS. Moreover, increased circulating concentrations of CCL20 (and other chemokines) was registered over time, consistent with the prolonged durations of viral shedding in COVID-19

patients [35] .

The efforts made by the scientific community in recent months have made it clear that COVID-19 displays a kind of "inflammatory signature", characterized by increased levels of soluble biomarkers (cytokine and chemokines) which are involved in the recruitment and activation of several immune cell types, like monocyte/macrophages, neutrophils, T-lymphocytes, and many others. These immune-active biomarkers, measured either early upon patient admission or throughout hospitalization, may provide clinically relevant information in predicting a more or less severe course of the disease as well as in estimating the mortality risk of infected patients. However, despite the above stated considerations, based on the currently available data, we will attempt to indicate those chemokines that, at least at present, were more firmly identified to represent the "chemokine immune signature" in COVID-19.

By "chemokine immune signature" we are referring to a sort of identity card of a specific circulating chemokine profile of a patient with COVID-19, which would confer a given clinical phenotype of the infection. In particular, the "chemokine immune signature" may hold diagnostic, prognostic and therapeutic implications of patients infected with SARS-COV-2. This could represent an additional tool, helping clinicians in predicting the disease severity and outcome of a given patients and clinical decision making. Based on the currently available studies which were overviewed in the present review, CXCL10 and CCL2 could be reasonably regarded as the two chemokines, for which more solid and consistent data would support a crucial role in determining the clinical course and ultimately the outcome of COVID-19. It should be added that, both CXCL10/CXCR3 and CCL2/CCR2 axes would deserve to be more deeply investigated in terms of their potential as therapeutic targets.

The idea that CXCL10 and CCL2 should be regarded as "dominant" in the chemokine immune signature stems from the number of studies consistently reporting their crucial role in the onset of the cytokine storm of COVID-19 and from their relevance in determining specific features of this J o u r n a l P r e -p r o o f condition. Indeed, among the several chemokines which have been evaluated and found to be involved in COVID-19, CXCL10 and CCL2 were found to be the most up-regulated ones as compared to controls, showing different degrees of correlation with the viral load as well as with several peculiar symptoms (asthenia, dyspnea, anosmia) [5, 7-11, 21-23, 29, 36, 37, 44-46, 49, 54, 65-67] . Most importantly, CXCL10 and CCL2 were identified to be rather good markers of disease severity since their circulating levels progressively increase in patients with moderate, mild and severe clinical manifestations. Furthermore, CXCL10 and CCL2 were considered potential initiators of the deadly COVID-19 immuno-pathological pathway being correlated to increased risk of mortality [11, 13] . From a biological point of view, the circulating levels of these chemokines crucially determine the recruitment of a specific immune cell milieu infiltrating lungs in COVID-19

patients. As previously stated, the type and the abundance of cell infiltrate will be crucial in the development of the feedback loop characterizing the cytokine storm. In particular, on one hand, CXCL10 recruits monocytes and macrophages expressing CXCR3 sustaining the early Th1 oriented immune response of COVID-19 patients [66] , on the other hand, CXCL10 by selectively binding endothelial cells expressing the CXCR3 receptor, will impair endothelial integrity [68] , which is on chemokine levels early in disease might also provide relevant information for healthcare in allocation and prioritization of the highest-risk patients. As a final consideration, given that it seems reasonable to propose that early immunological interventions targeting inflammatory markers specifically predicting a more severe disease outcome, could be more effective than those modulating late-appearing chemokines.

In the last few months, rapidly growing evidences supporting an important role of chemokines in SARS-COV-2 enters lung cells by binding to the ACE-2 receptor (A); Intracellular viral replication is followed by cell stress/damage, inducing pyro-ptosis, which in turn produces several damageassociated-molecular-patterns (i.e. ATP, oligomers and nucleic acids) (B); As a consequence, resident lung cells start secreting chemokines (C); which will, in turn recruit immune cells expressing the specific chemokine receptor, through a multistep process involving adherence and migration across the endothelium, trafficking through the interstitium, and finally moving the site of J o u r n a l P r e -p r o o f 23 the infection (D); Infiltrating immune cells start secreting pro-inflammatory cytokines (E); the onset and maintenance of this pro-inflammatory feed-back loop will result in mainteinance of chemokines secretion which will perpetuate the recruitment of infiltrating immune cells.

The above described events will ultimately result in the cytokine storm which will subsequently spread to other organs, eventually leading to multi-organ failure.

This paper was not supported by any grant or funding

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

Coronavirus disease (COVID-19) pandemic

Immunological decision-making: how does the immune system decide to mount a helper T-cell response?

The chemokine system in innate immunity

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

Heightened Innate Immune Responses in the Respiratory Tract of COVID-19 Patients

Single-cell landscape of bronchoalveolar immune cells in patients with COVID-19

COVID-19 severity correlates with airway epithelium-immune cell interactions identified by single-cell analysis

Serum Cytokine and Chemokine Profile in Relation to the Severity of Coronavirus Disease 2019 in China

Longitudinal analyses reveal immunological misfiring in severe COVID-19

Imbalanced Host Response to SARS-CoV-2 Drives Development of COVID-19

A Human Pluripotent Stem Cell-based Platform to Study SARS-CoV-2 Tropism and Model Virus Infection in Human Cells and Organoids

Preventing Mortality in COVID-19 Patients: Which Cytokine to Target in a Raging Storm?

GROα promotes invasion of colorectal cancer cells

Constitutive overexpression of a growth-regulated gene in transformed Chinese hamster and human cells

A Novel CD206 Targeting Peptide Inhibits Bleomycin Induced Pulmonary Fibrosis in Mice

CXCL8 in thyroid disease: from basic notions to potential applications in clinical practice

Role of Chemokines in Thyroid Cancer Microenvironment: Is CXCL8 the Main Player?

Type I and Type III Interferons Restrict SARS-CoV-2 Infection of Human Airway Epithelial Cultures

Correlation Between Relative Nasopharyngeal Virus RNA Load and Lymphocyte Count Disease Severity in Patients with COVID-19

Clinical and pathological investigation of patients with severe COVID-19

Clinical features of patients infected with 2019 novel coronavirus in

Heightened Circulating Interferon-Inducible Chemokines, and Activated Pro-Cytolytic Th1-Cell Phenotype Features Covid-19 Aggravation in the Second Week of Illness

Multisystem inflammatory syndrome in children and COVID-19 are distinct presentations of SARS-CoV-2

An inflammatory cytokine signature helps predict COVID-19 severity and death, medRxiv

Phase I trial of HuMax-IL8 (BMS-986253), an anti-IL-8 monoclonal antibody, in patients with metastatic or unresectable solid tumors

CXCL9, CXCL10, CXCL11/CXCR3 axis for immune activation -A target for novel cancer therapy

Role of chemokines in endocrine autoimmune diseases

Immune response in children with COVID-19 is characterized by lower levels of T-cell activation than infected adults

CXC chemokines in angiogenesis

CXCR3-mediated opposite effects of CXCL10 and CXCL4 on TH1 or TH2 cytokine production

The cytokine storm in COVID-19: An overview of the involvement of the chemokine/chemokine-receptor system

Plasma IP-10 and MCP-3 levels are highly associated with disease severity and predict the progression of COVID-19

CXCL10 an important chemokine associated with cytokine storm in COVID-19 infected patients

Uncontrolled Innate and Impaired Adaptive Immune Responses in Patients with COVID-19 ARDS

IP-10 and MCP-1 as biomarkers associated with disease severity of COVID-19

P.s. group, CXCL10 could drive longer duration of mechanical ventilation during COVID-19 ARDS

Elevated serum interferon-gamma-inducible chemokine-10/CXC chemokine ligand-10 in autoimmune primary adrenal insufficiency and in vitro expression in human adrenal cells primary cultures after stimulation with proinflammatory cytokines

Real-time IP-10 measurements as a new tool for inflammation regulation within a clinical decision support protocol for managing severe COVID-19 patients

The MCP/eotaxin subfamily of CC chemokines

Targeting the CCL2-CCR2 signaling axis in cancer metastasis

Monocyte chemoattractant protein-1 (MCP-1): an overview

An immune-based biomarker signature is associated with mortality in COVID-19 patients

Factors of Severity in Patients with COVID-19: Cytokine/Chemokine Concentrations, Viral Load, and Antibody Responses

Association of Early Nasopharyngeal Immune Markers With COVID-19 Clinical Outcome: Predictive Value of CCL2/MCP-1

Macrophage inflammatory protein-1

Macrophage inflammatory protein-1alpha is induced by human immunodeficiency virus infection of monocytederived macrophages

Clinical course and risk factors for mortality of adult inpatients with COVID-19 in Wuhan, China: a retrospective cohort study

Mapping Systemic Inflammation and Antibody Responses in Multisystem Inflammatory Syndrome in Children (MIS-C)

The inflammatory chemokine CCL5 and cancer progression

The inflammatory chemokines CCL2 and CCL5 in breast cancer

Gene-engineered T cells for cancer therapy

Immune environment modulation in pneumonia patients caused by coronavirus: SARS-CoV, MERS-CoV and SARS-CoV-2

Longitudinal COVID-19 profiling associates IL-1RA and IL-10 with disease severity and RANTES with mild disease

Sex differences in immune responses that underlie COVID-19 disease outcomes

Disruption of the CCL5/RANTES-CCR5 Pathway Restores Immune Homeostasis and Reduces Plasma Viral Load in Critical COVID-19, medRxiv

Signaling Pathways, and Adjuvant Functions in Viral Infection and Prevention

Solution Structure of CCL19 and Identification of Overlapping CCR7 and PSGL-1 Binding Sites

Higher plasma levels of Chemokine CCL19 are associated with poor SARS-CoV-2 acute respiratory distress syndrome (ARDS) outcomes

Genomic organization of the CC chemokine mip-3alpha/CCL20/larc/exodus/SCYA20, showing gene structure, splice variants, and chromosome localization

CCR6 as a mediator of immunity in the lung and gut

Molecular cloning of a novel human CC chemokine activation-regulated chemokine (LARC) expressed in liver. Chemotactic activity for lymphocytes and gene localization on chromosome 2

The dysregulated innate immune response in severe COVID-19 pneumonia that could drive poorer outcome

IP-10 induces dissociation of newly formed blood vessels

Exuberant elevation of IP-10, MCP-3 and IL-1ra during SARS-CoV-2 infection is associated with disease severity and fatal outcome

Pathological inflammation in patients with COVID-19: a key role for monocytes and macrophages