key: cord-0909354-l7uwtdxu
authors: Chen, Hao; Zhang, Xinyu; Liu, Wanjun; Xue, Mingshan; Liao, Chenxi; Huang, Zhifeng; Hu, Haisheng; Sun, Baoqing
title: The role of serum specific- SARS-CoV-2 antibody in patients with COVID-19
date: 2020-12-24
journal: Int Immunopharmacol
DOI: 10.1016/j.intimp.2020.107325
sha: 8b5ec0e7aa4c5203cf192d93ca71dea1c05bf297
doc_id: 909354
cord_uid: l7uwtdxu

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), responsible for coronavirus disease 2019 (COVID-19), has rapidly spread, resulting in considerable casualties and serious economic loss worldwide. Disease severity and related symptoms markedly vary among individuals. A large number of patients present atypical symptoms, which represent a big challenge for early diagnosis and prompt infection source isolation. Currently, COVID-19 diagnosis predominantly depends on nucleic acid tests (NAT) for SARS-CoV-2 in respiratory specimens, but this method presents a high rate of false negative results. Therefore, serum antibody measurement has been rapidly developed as a supplementary method with the aim of improving diagnostic accuracy. Further, serum antibody levels might help to identify the infection stage, asymptomatic carriers, and patients with diverging severities and to monitor convalescent plasma therapy. In the current review, we aim to present comprehensive evidence to clarify the utility of SARS-CoV-2 antibodies measurement for COVID-19 diagnosis as a reference for use in the clinic.

The novel coronavirus infection was first reported at the end of December 2019 in Wuhan, China. Later, the cause of pneumonia cases of unknown etiology was confirmed to be a new coronavirus infection. The World Health Organization (WHO) named it coronavirus disease 2019 (COVID- 19) , and the responsible virus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In January 2020, this communicable disease rapidly spread across the country and overseas. COVID-19 is characterized by rapid transmission, atypical clinical symptoms, and the potential to be easily misdiagnosed. In particular, the numerous asymptomatic carriers are major obstacles for prevention and control. Chen, 3 3 Currently, the gold standard for COVID-19 diagnosis is the nucleic acid test (NAT) for SARS-CoV-2 by reverse transcription-polymerase chain reaction (RT-PCR). However, due to factors such as sample quality, personnel handling, testing equipment, and many others, this detection method may result in a number of false negatives. In hospital in Wuhan, 4880 patients with respiratory infection symptoms or close contact with COVID-19 patients were tested using RT-PCR, finding positive NAT rates in nasopharyngeal swabs, sputum, and bronchoalveolar lavage were 38.25%, 49.12%, and 80%, respectively [1] . The low positive rates in nasopharyngeal swabs and sputum samples might be due to the localized involvement in the lung at the disease stage [2] . Although the positive detection rate with sample from the lower respiratory tract is high, obtaining these samples is difficult, especially for outpatients, and there is a risk of infection and/or virus diffusion during the sampling process. Serological antibody tests are fast processing, convenient, obtainable, and highly sensitive. For the aforementioned reasons, serum antibody tests have been rapidly developed as a supplemental tool in COVID-19 diagnosis. Additionally, serum antibodies are important for assessing the severity of COVID-19, helping diagnose asymptomatic SARS-COV-2 infections, and in screening the best convalescent plasma donors.

In order to provide a reference for clinicians, we have reviewed the role of serum specific SARS-CoV-2 antibodies in patients with COVID-19..

Immunoglobulin (Ig) M, IgA, and IgG are the antibody types most commonly used in COVID-19 diagnosis. IgM mediates the primary immune response, and the detection of specific IgM indicates a recent infection. Serotype IgA is a monomer that mainly exists in the serum and participates in humoral immunity.

IgG is the most abundant isotype (75%-80%), has the longest half-life (20-23 days) in the serum and extracellular fluid, and is the main antibody involved in the secondary immune response. Chen, 4 4 Li et al [3] found that after SARS-CoV-2 infection in humans, specific antibodies can be produced in 15 days. Specific IgM and IgA can be detected in 3-6 days, and IgM can rise to its highest levels 8-14 days after symptom onset. While the IgA level continues to rise for 0-14 days following symptom onset and thereafter ceases to increase. IgG can be detected 14 days after symptom onset, with level rising during days 8-21, and stabilizing after 21 days, and remains present in the later stages of infection [3] . Liu et al. found an increase in IgM titers on day 4 after SARS-CoV-2 infection, reaching a peak approximately on day 20, whereas IgG could be identified on day 7 after infection, peaking around day 25 [4] . Xu et al. found that the cumulative seropositivity rates for IgM and IgG were 44% and 56% on day 7 after symptom onset, respectively, and reached more than 95% on day 20 and day 16, respectively, with both IgM and IgG antibody levels remaining above the threshold on day 28, a different observation from the time of antibody appearance and persistence in other studies [5] .

Compared with specific IgM and IgG, IgA has not shown obvious advantages in the diagnosis of SARS-COV infection [6] . In influenza virus infections, protective secretory IgA can be found in asymptomatic or mildly symptomatic cases [7] . IgA measurements have been shown to be more sensitive than IgM measurements in detecting hepatitis B virus infection, with levels being associated with the severity of liver disease [8] . In patients infected with SARS-CoV-2, IgA and IgM appeared for a similar time period, and IgA titers and detection rate were higher than those of IgM [3] . These characteristics differ from those of SARS-CoV infection. A study by Yu et al. [9] showed that the first IgA seroconversion day was 2 days after initial symptoms onset in COVID-19 patients, and that of IgM and IgG was 5 days after onset, the levels of specific IgA antibodies were significantly higher than those of IgM. Padoan et al. [10] found that the IgA response appears and grows early, peaks at week 3, and is stronger and more persistent than the IgM response. Jääskeläinen et al. [11] also found that IgA testing could be useful together with IgG in COVID-19 patients with atypical symptoms or suspected cases with negative NAT. Therefore, IgA may Chen, 5 5 be useful for diagnosing patients with acute stage infection or asymptomatic carriers. Presently, the detection of IgM and IgG isotypes is widely applied in clinical practice, but the diagnostic value of IgA in COVID-19

has not received enough attention and requires further research.

IgM and IgG have a reciprocal relationship; therefore, the simultaneous detection of IgM and IgG antibodies is more suitable for patients with COVID-19 at an unclear infection stage. In a study evaluating the sensitivity and specificity of IgG/IgM combined antibodies, the combined antibodies showed superiority to IgM or IgG tests alone [12] . Not only can combined antibody detection improve diagnostic accuracy and infection control, but it can also be employed to assess disease progression and monitor long-term dynamic.

The diagnostic efficacy of SARS-COV-2 specific antibodies varies greatly according to various research results, most likely due to the different antibody detection methods, specific proteins targeted, and various products. Cassaniti 

Asymptomatic SARS-CoV-2 carriers are uncertain factors in the prevention and control of the current epidemic. Asymptomatic COVID-19 infection has no clinical symptoms (such as fever, cough, or sore throat) and no radiological changes to the lung, yet NAT is positive for SARS-CoV-2. In a recent COVID-19 study, the viral load of upper respiratory tract samples was similar for both asymptomatic and symptomatic patients, suggesting that the potential for viral transmission by asymptomatic or mildly symptomatic patients is comparable to that of symptomatic patients [18] . Therefore, early screening and isolation of asymptomatic carriers is of great significance for controlling the spread of the epidemic. Currently, the screening of asymptomatic infected persons mainly relies on NAT, but its false positive rate leads to a serious underestimation of the proportion of asymptomatic infected persons. In Spain, 5% of the population is serologically positive, and one-third of these people do not report symptoms [19] . Guangzhou reported that 44% of people infected with SARS-CoV-2 were asymptomatic [20] . In a study by Huang et al. the

proportion of patients with asymptomatic infections was 20.8% [21] . Dong et al suggested that conducting Chen, 7 7 large-scale serological studies on SARS-CoV-2 specific IgG could improve the ability to predict the epidemiological characteristics of asymptomatic infections [22] .

China's wildlife market in Guangzhou showed that 14.86% of the staff had been exposed to SARS-CoV but did not show obvious clinical symptoms [23, 24] . Similarly, the Middle East respiratory syndrome coronavirus (MERS-CoV) infection may be asymptomatic or cause a mild influenza-like disease [25] ; in The results showed that the ratio of serum antibodies was increased in the high-risk group, which confirmed the significance of IgG in MERS and highlighted the complementary effect of IgM and IgG detection.

Studies on Ebola virus also reached similar conclusions. In a study of 24 asymptomatic individuals, 11

produced specific IgM and IgG against the Ebola virus, indicating clear serological changes in asymptomatic individuals [27] .

Several studies suggest that asymptomatic SARS-CoV-2 carries are in the incubation period and have the ability to transmit the virus [28] [29] [30] . The mean shedding time (19 days) was significantly longer in asymptomatic individuals than in symptomatic ones [21] , suggesting that asymptomatic patients may have a different immune response to SARS-COV-2 infection. Meanwhile, IgG levels in the symptomatic group were significantly higher than those in the asymptomatic group in the acute and early convalescent phase [21] . Chen et al. revealed that serological testing is useful for the identification of asymptomatic or subclinical infections of SARS-CoV-2 among those in close contact with COVID-19 patients [31] . The study by Long [32] also showed that serological antibody testing helps diagnose RT-PCR negative patients with suspected and asymptomatic infections and is essential for the accurate estimation of COVID-19 Chen, 8 8 prevalence. Lei [33] also observed that NAT binding to specific IgM can significantly improve detection sensitivity compared with NAT alone. Therefore, screening asymptomatic patients for serum antibodies can effectively identify the source of infection and control further COVID-19 outbreaks.

Although serological antibody tests can serve as a diagnostic tool, there is also evidence that the levels of antibodies are representative indicators of COVID-19. Quantification of antibody levels in patients with varying COVID-19 severity is essential to assess patient prognosis. A single-center, retrospective cohort study showed that [34] for IgM titers≥50 AU/ml, patients with severe/critical COVID-19 are at a higher risk of clinical adverse events; therefore, the reduction in IgM titers in severe/critical cases may be indicative of a better prognosis. Hou et al. [35] found that in COVID-19 patients, severe and critical cases had higher IgM levels than mild cases, whereas the IgG levels in critical cases were lower than those in both mild and severe cases. Caturegli et al. [36] showed that SARS-CoV-2 antibodies predict the odds of developing acute respiratory distress syndrome, with a 62% increase in incidence for every 2-fold increase in IgG. Similar results could be obtained with a test for neutralizing antibodies. Liu L et al [37] suggested that ICU patients had an accelerated and augmented neutralizing antibody response compared to non-ICU patients, which was associated with disease severity. Our previous research [38] also found that IgA and IgG levels were higher in severe and critical COVID-19 patients than in moderate ones, while IgM levels were did not differ between the two groups. The relationship between SARS-CoV-2 specific antibodies and the severity and prognosis of COVID-19 has not been conclusively established, but existing studies support the view that the higher the level of antibodies, the more severe is the disease and the poorer is the prognosis. Therefore, quantitative detection of serum antibodies may have potential significance for evaluating the severity and prognosis of COVID-19. However, it may be necessary to include more patients Chen, 9 9 with COVID-19 as well as studies including antibodies against different proteins to derive further conclusions.

Recovery plasma contains specific polyclonal antibodies, which have been used in the treatment of SARS, MERS, Ebola, and other infectious diseases. Several studies have shown that in patients with SARS, those who received recovery plasma treatment had shorter hospital stays and lower mortality than those who did not [39] [40] [41] . In addition, convalescent plasma infusion is considered the most promising treatment for MERS-CoV infection [42, 43] , and convalescent plasma collected from Ebola patients was recommended in 2014 as an empirical treatment during outbreaks. Because of the comparable virological and clinical characteristics among SARS, MERS, and COVID-19 [44] , convalescent plasma may be effective for the treatment of COVID-19. Some reports have shown that plasma therapy can effectively reduce the symptoms and mortality of patients with SARS-CoV-2 infection when there is no specific treatment for COVID-19 [45] [46] [47] , and convalescent plasma transfusion has shown good safety results in hospitalized patients with COVID-19 [48] .

Neutralizing antibodies are antibodies against viral surface antigens, which can bind to the free virus in the body to prevent it from being absorbed and invade cells. IgM, IgG, and IgA possess neutralizing antibody activity, and IgG, especially the S-RBD-specific IgG, plays an important role in plasma therapy during the recovery period due to its high content in body fluid, high specificity, and long-term existence after recovery. A study on plasma therapy for five severe COVID-19 patients showed good therapeutic effect and [47] the selected plasma donors were required to meet the following conditions: at least 10 days without symptoms during the recovery period, a titer of serum SARS-CoV-2 specific IgG antibody higher than 1:1000 (detected by ELISA), a neutralizing antibody titer higher than 40, and same-day infusion into Chen, 10 10 the patients with COVID-19 receiving treatment. The titers of the specific IgG and IgM in the receptor binding domain and the neutralizing antibody against SARS-CoV-2 were 1800-16200 and 80-480, respectively, as determined using ELISA. After infusion, patients should be continuously monitored for at least 1 week to ensure a time-dependent increase in IgM and IgG levels.

Convalescent plasma therapy may result in increased antibody dependence, which may lead to more severe disease only in a subset of genetically susceptible patients [49] ; therefore, special attention should be paid to the timing of plasma therapy. In order to improve the body's humoral immune response, reduce the repeated stimulation of killer T cells on the human immune system, and avoid a cytokine storm, patients should receive infusions when they have not produced IgG antibodies. Presently, the National Health

Commission of China recommends collecting plasma within two weeks after the recovery period [50] . A study indicates that the S-RBD-specific IgG antibody reaches high levels four weeks after the onset of COVID-19 symptoms; therefore, the researchers recommended that donors should wait four weeks after symptoms' onset before considering donating plasma [51] . In the process of plasma treatment, dynamic screening of specific antibodies is required for both donors and patients.

Generally, when patients have suspected symptoms of COVID-19 and the NAT for SARS-CoV-2 is negative, SARS-CoV-2 specific IgM/IgG antibodies can be used as diagnostic standard for COVID-19 and antibodies to different proteins have differing sensitivities and specificities [56] . Antibodies against the S-protein have a higher specificity, while those against the N-protein have a higher sensitivity [57] . To engage the host cell receptor human angiotensinconverting enzyme 2 (hACE2), the S-protein undergoes dramatic conformational changes to expose the RBD and key residues for receptor binding [58] .

Considering the critical role of RBD in initiating SARS-CoV-2 invasion into host cells, it is a vulnerable target for neutralizing antibodies. Theoretically, the neutralizing antibody binds to RBD on the S-protein, but it may also bind to other domains; therefore, the screening of neutralizing antibodies needs to be verified by neutralizing the live virus at the cellular level. However, it is important to note that the detection of antibodies, especially IgG, does not indicate a certain immunity to SARS-CoV-2, but only a present or past infection. Chen, 13 13 Since RT-PCR can produce a false-negative result in viral NAT, especially in nasopharyngeal swabs, COVID-19 should be diagnosed using a combination of NAT and clinical symptoms [59] . However, COVID-19 does not show the same typical clinical symptoms as those observed in individuals infected with SARS, MERS, and Ebola virus. In particular, there are a large number of asymptomatic SARS-CoV-2 carriers. Antibody detection is a useful adjunct to RT-PCR detection and can improve the accuracy of COVID-19 diagnosis, thus providing an effective complement to NAT for the diagnosis of SARS-CoV-2

infection. Further, antibody detection has clinical significance for determining the stage of infection and identifying asymptomatic carriers, evaluating the severity of disease, and evaluating the progress of plasma treatment during the recovery period (summarized in Table 3 ).

This study was supported by the Zhejiang University special scientific research funding for COVID-19

prevention and control (2020XGZX001, 2020XGZX025).

Positive rate of RT-PCR detection of SARS-CoV-2 infection in 4880 cases from one hospital in

Profiling Early Humoral Response to Diagnose Novel Coronavirus Disease (COVID-19)

Patterns of IgG and IgM antibody response in COVID-19 patients

Seroprevalence of immunoglobulin M and G antibodies against SARS-CoV-2 in China

Detection of specific antibodies to severe acute respiratory syndrome (SARS) coronavirus nucleocapsid protein for serodiagnosis of SARS coronavirus pneumonia

Role of IgA versus IgG in the control of influenza viral infection in the murine respiratory tract

Serum Immunoglobulin A (IgA) Level Is a Potential Biomarker Indicating Cirrhosis during Chronic Hepatitis B Infection

Distinct features of SARS-CoV-2-specific IgA response in COVID-19 patients

IgA-Ab response to spike glycoprotein of SARS-CoV-2 in patients with COVID-19: A longitudinal study

Evaluation of commercial and automated SARS-CoV-2 IgG and IgA ELISAs using coronavirus disease (COVID-19) patient samples

Development and Clinical Application of A Rapid IgM-IgG Combined Antibody Test for SARS-CoV-2 Infection Diagnosis

Performance of VivaDiag COVID-19 IgM/IgG Rapid Test is inadequate for diagnosis of COVID-19 in acute patients referring to emergency room department

Diagnostic value and dynamic variance of serum antibody in coronavirus disease 2019

Clinical evaluation of a rapid colloidal gold immunochromatography assay for SARS-Cov-2 IgM/IgG

Reliability and usefulness of a rapid IgM-IgG antibody test for the diagnosis of SARS-CoV-2 infection: A preliminary report

Antibody Detection and Dynamic Characteristics in Patients with COVID-19

SARS-CoV-2 Viral Load in Upper Respiratory Specimens of Infected Patients

Prevalence of SARS-CoV-2 in Spain (ENE-COVID): a nationwide, population-based seroepidemiological study

Temporal dynamics in viral shedding and transmissibility of COVID-19

Clinical and immunological assessment of asymptomatic SARS-CoV-2 infections

Eleven Faces of Coronavirus Disease

Prevalence of IgG antibody to SARS-associated coronavirus in animal traders

Severe acute respiratory syndrome-associated coronavirus infection

Seroprevalence of MERS-CoV in healthy adults in western Saudi Arabia

Comparative Serological Study for the Prevalence of Anti-MERS Coronavirus Antibodies in High-and Low-Risk Groups in Qatar

Human asymptomatic Ebola infection and strong inflammatory response

Clinical characteristics of 24 asymptomatic infections with COVID-19 screened among close contacts in Nanjing

Transmission of 2019-nCoV Infection from an Asymptomatic Contact in Germany

A familial cluster of pneumonia associated with the 2019 novel coronavirus indicating person-to-person transmission: a study of a family cluster

High SARS-CoV-2 antibody prevalence among healthcare workers exposed to COVID-19 patients

Antibody responses to SARS-CoV-2 in patients with COVID-19

Antibody dynamics to SARS-CoV-2 in asymptomatic COVID-19 infections

Serum IgM against SARS-CoV-2 correlates with in-hospital mortality in severe/critical patients with COVID-19 in Wuhan

Detection of IgM and IgG antibodies in patients with coronavirus disease 2019

Clinical Validity of Serum Antibodies to SARS-CoV-2: A Case-Control Study

High neutralizing antibody titer in intensive care unit patients with COVID-19

Characteristics and roles of severe acute respiratory syndrome coronavirus 2-specific antibodies in patients with different severities of coronavirus 19

Treatment of severe acute respiratory syndrome

Retrospective comparison of convalescent plasma with continuing high-dose methylprednisolone treatment in SARS patients

Use of convalescent plasma therapy in SARS patients in Hong Kong

The Effectiveness of Convalescent Plasma and Hyperimmune Immunoglobulin for the Treatment of Severe Acute Respiratory Infections of Viral Etiology: A Systematic Review and Exploratory Meta-analysis

Current treatment options and the role of peptides as potential therapeutic components for Middle East Respiratory Syndrome (MERS): A review

Emerging threats from zoonotic coronaviruses-from SARS and MERS to 2019-nCoV

The Use of TKM-100802 and Convalescent Plasma in 2 Patients With Ebola Virus Disease in the United States

Passive Immunotherapy: Assessment of Convalescent Serum Against Ebola Virus Makona Infection in Nonhuman Primates

Treatment of 5 Critically Ill Patients With COVID-19 With Convalescent Plasma

Early safety indicators of COVID-19 convalescent plasma in 5,000 patients

Current studies of convalescent plasma therapy for COVID-19 may underestimate risk of antibody-dependent enhancement

The epidemiology, diagnosis and treatment of COVID-19

Effect of Convalescent Plasma Therapy on Time to Clinical Improvement in Patients With Severe and Life-threatening COVID-19: A Randomized Clinical Trial

Seasonal influence on TORCH infection and analysis of multi-positive samples with indirect immunofluorescence assay

Serum IgG ACPA-IgM RF immune complexes were detected in rheumatoid arthritis patients positive for IgM ACPA

Association between false-positive TORCH and antiphospholipid antibodies in healthy pregnant women

False Positive Lyme Disease IgM Immunoblots in Children

Review of Current Advances in Serologic Testing for COVID-19

Detection of Nucleocapsid Antibody to SARS-CoV-2 is More Sensitive than Antibody to Spike Protein in COVID-19 Patients

Human monoclonal antibodies block the binding of SARS-CoV-2 spike protein to angiotensin converting enzyme 2 receptor

Combination of RT-qPCR testing and clinical features for diagnosis of

17 of SARS-CoV-2 outbreak

 Propose the importance of SARS-COV-2 specific antibody detection

 Suggests the importance of complementarity between nucleic acid test and antibody

 Provide a reference for the current diagnosis and treatment of COVID-19