10
views
0
recommends
+1 Recommend
2 collections
    0
    shares
      • Record: found
      • Abstract: found
      • Article: found

      Significance of IgA antibody testing for early detection of SARS‐CoV‐2

      letter
      1 ,
      Journal of Medical Virology
      John Wiley and Sons Inc.

      Read this article at

      ScienceOpenPublisherPMC
      Bookmark
          There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.

          Abstract

          To the Editor, Serological detection of severe acute respiratory syndrome coronavirus‐2 (SARS‐CoV‐2)‐specific antibody is usually limited to immunoglobulin M (IgM), IgG, and total antibodies, comprising IgA, IgM, and IgG. 1 , 2 , 3 IgA antibodies are less frequently used for SARS‐CoV‐2 detection as IgM‐ and IgG‐based assays are the gold standard for serological diagnosis. Traditionally, IgM antibodies are considered as a serological marker of a recent or acute infection. However, SARS‐CoV‐2‐specific IgA, IgM, and IgG can be detected after the onset of symptoms at different time points. 2 , 3 The kinetics of seroconversion vary significantly between different antibody detection kits due to differences in SARS‐CoV‐2 epitopes, antibody isotypes, and variations in analytical sensitivities associated with different chemistries. Antibodies against S protein are generated later than those against the N protein in SARS‐CoV‐2 infection. Herroelen et al. 4 observed that seroconversion of antibody against S‐RBD was earlier than seroconversion against N protein, suggesting that the time of seroconversion being detected depends on the patient's immune condition and the design of the assay. Performance of the antibody kit can be enhanced by the inclusion of IgA with IgG isotypes. 4 Recent studies showed that IgA might also play an important role in the immune response and disease progression. 5 In a study comparing different assays, it was shown that IgA appeared early in SARS‐CoV‐2 infection. With a small sample size of patients (n = 30), who were IgM‐negative and polymerase chain reaction (PCR)‐positive for SARS‐CoV‐2, 26.6% (8/30) of the patients tested positive for IgA at days 5–7 post‐onset. Although the samples are limited, these results suggest that the presence of IgA antibodies is superior to IgM as an early serological marker of recent SARS‐CoV‐2 infections. 6 Guo et al used an indirect enzyme‐linked immunosorbent assay (ELISA) for detection of IgA, IgM, and IgG against SARS‐CoV‐2 using purified recombinant N protein as antigen. 3 The median duration for detection of IgA and IgM was 5 days after symptom onset and 14 days for IgG. A commercially available S1‐protein‐based IgA ELISA assay by Euroimmun was evaluated. The assay had good sensitivity and showed a quantitative relationship with higher neutralizing antibody titers. 1 Using a SARS‐CoV‐2 S protein‐specific chemiluminescent immunoassay, Yu et al. found that the first day of IgA, IgM, and IgG seroconversion was 2, 5, and 5 days post‐symptom onset, respectively. Of 183 samples from 37 patients, the positivity rate of antibodies was 98.9%, 93.4%, and 95.1% for IgA, IgM, and IgG, respectively. 5 The early detection capacity of IgA could be a valuable addition to the IgG assay. 1 IgA assays showed early detection capacity with low specificity. Not surprisingly, it is puzzling why seroconversion of IgA antibodies can be detected early, sometimes within 2 days of symptom onset. 5 Several possibilities may account for this. Admission time may be mistaken for onset time. Another possibility is a rapidly triggered nonspecific IgA memory response, probably due to previous infections with common cold coronaviruses, resulting in detectable IgA levels within 2 days. 1 , 7 The third possibility may be rapid T‐cell‐independent production of IgA in general or by cross‐reacting with previously experienced common cold coronaviruses. 8 , 9 IgA is abundant in serum, nasal mucus, saliva, breast milk, and intestinal fluids, accounting for 10% to 15% of human immunoglobulins. For acute SARS‐CoV‐2 infection, IgA detection could be helpful along with IgG in patients with atypical symptoms or when RNA testing is repeatedly negative for a suspected patient. 10 Low sensitivity renders a saliva IgA assay unsuitable for serological screening of suspected COVID‐19 patients. 11 However, it is well‐known that IgA plays a central role in mucosal immunity, which is important in protection against respiratory infections. A saliva IgA assay can be of importance to evaluate the level of protective immunity in recovered patients or the efficiency of a vaccine when available in the near future. Considering the early detection characteristics of IgA, it should be recommended for inclusion in serological test kits. An IgA assay can be valuable when SARS‐CoV‐2 RNA testing remains negative in patients with suspected chest computed tomography/symptoms or if no PCR facility is available. IgA testing could be a good alternative way to shorten the SARS‐CoV‐2 diagnosis turnaround time. Importantly, laboratories and clinicians must be familiar with the significance of IgA and know how to interpret the serological testing results. For policymakers, IgA antibody should be given higher priority for implementation in current clinical and public practice. CONFLICT OF INTERESTS The author declare that there are no conflict of interests.

          Related collections

          Most cited references11

          • Record: found
          • Abstract: found
          • Article: not found

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

          Abstract Background The emergence of coronavirus disease 2019 (COVID-19) is a major healthcare threat. The current method of detection involves a quantitative polymerase chain reaction (qPCR)–based technique, which identifies the viral nucleic acids when present in sufficient quantity. False-negative results can be achieved and failure to quarantine the infected patient would be a major setback in containing the viral transmission. We aim to describe the time kinetics of various antibodies produced against the 2019 novel coronavirus (SARS-CoV-2) and evaluate the potential of antibody testing to diagnose COVID-19. Methods The host humoral response against SARS-CoV-2, including IgA, IgM, and IgG response, was examined by using an ELISA-based assay on the recombinant viral nucleocapsid protein. 208 plasma samples were collected from 82 confirmed and 58 probable cases (qPCR negative but with typical manifestation). The diagnostic value of IgM was evaluated in this cohort. Results The median duration of IgM and IgA antibody detection was 5 (IQR, 3–6) days, while IgG was detected 14 (IQR, 10–18) days after symptom onset, with a positive rate of 85.4%, 92.7%, and 77.9%, respectively. In confirmed and probable cases, the positive rates of IgM antibodies were 75.6% and 93.1%, respectively. The detection efficiency by IgM ELISA is higher than that of qPCR after 5.5 days of symptom onset. The positive detection rate is significantly increased (98.6%) when combining IgM ELISA assay with PCR for each patient compared with a single qPCR test (51.9%). Conclusions The humoral response to SARS-CoV-2 can aid in the diagnosis of COVID-19, including subclinical cases.
            Bookmark
            • Record: found
            • Abstract: found
            • Article: found
            Is Open Access

            Serum IgA, IgM, and IgG responses in COVID-19

            Currently, detecting SARS-CoV-2 RNAs is a standard approach for COVID-19 diagnosis. However, there is an urgent need for reliable and rapid serological diagnostic methods to screen SARS-CoV-2-infected people including those who do not have overt symptoms. Most emerging studies described serological tests based on detection of SARS-CoV-2-specific IgM and IgG. 1–4 Although detection of SARS-CoV-2-specific IgA in serum has been reported in few papers, 5,6 analyses of IgA levels in a larger number of COVID-19 patients are still lacking. This study enrolled a total of 87 confirmed COVID-19 patients (Supplementary Table 1) who were admitted to the First Affiliated Hospital of USTC Hospital or the First Affiliated Hospital of Anhui Medical University between January 26, and Mar 5, 2020. Their blood samples were collected during routine clinical testing. All enrolled cases were confirmed with SARS-CoV-2 infection by use of a standard RT-qPCR assay on throat swab samples from the respiratory tract. For all of the enrolled patients, the date of illness onset, clinical classifications of severity, RNA testing results during the hospitalization period, and the personal demographic information were obtained from the clinical records. Highly purified receptor-binding domain (RBD) of the SARS-CoV-2 spike protein (Supplementary Fig. 1) was expressed in human 293F cells and used to make a set of chemical luminescence kits for detecting the presence of RBD-specific IgA, IgM, and IgG, respectively. To evaluate the diagnostic power of the these kits, 216 sera from 87 SARS-CoV-2-infected patients and a total of 483 control sera including 330 healthy sera, 138 “interfering” sera of other-type patients and 15 sera from once-suspected pneumonia cases were tested. The detected signals relative light units (RLU), for each of isotype of the RBD-specific antibodies, were plotted (Fig. 1a–c). The RBD-specific IgA, IgM, and IgG kits showed diagnostic sensitivities of 98.6%, 96.8%, and 96.8%, and specificities of 98.1%, 92.3%, and 99.8%, respectively (Supplementary Fig. 2a–c). The sensitivities, specificities, and overall agreements of the RBD-specific IgA, IgM, or IgG kit and their combinations are also summarized in Supplementary Table 2. When combining the RBD IgA and IgG kits, the sensitivity, specificity, and overall agreement elevated to 99.1%, 100%, and 99.7%, respectively. This is better than those when IgM and IgG kits are combined using our data or the previous data shown by others. 1–4 Fig. 1 Analysis of SARS-CoV-2 RBD-specific IgA, IgM, and IgG antibodies in 87 COVID-19 patients. Testing results of RBD-specific IgA (a), IgM (b), and IgG (c) kits using 330 healthy sera, 138 sera from other-type of patients who may interfere with the test, 15 sera of once-suspected pneumonia patients, and 216 sera of 87 qPCR-confirmed COVID-19 patients. RLU relative light units. Black bar indicates median values. The dotted line indicates the cut-off value for detecting of each isotypes of antibodies. d Sensitivity of RBD-specific IgA, IgM, and IgG detection in serum samples obtained at different periods after illness onset. The kinetics of anti-RBD IgA, IgM, and IgG levels in sera of COVID-19 patients at different time windows was analyzed (e). The median values of RLU were plotted for each isotype of three antibodies. Bars indicate median with interquartile ranges. f–h Serum antibody levels in healthy and three distinct severity groups of COVID-19 patients were analyzed. Healthy: 330 sera; Mild: 7 sera; Moderate: 44 sera; and Severe: 21 sera. The critically ill patients were included into the severe group. Only the data of serum antibody levels at 16–25 days after illness onset of COVID-19 patients were used In order to investigate the seroconversion during COVID-19 pathogenesis, all the data from 216 sera samples were divided into six groups according to the time windows of collection after illness onset (Fig. 1d). At 4–10 days after symptom onset, the IgA kit exhibited the highest positive diagnostic rate as 88.2% (15/17), while IgM and IgG kit showed detection rates of 76.4% (13/17) and 64.7% (11/17), respectively. The 2 sera diagnosed as negative in the 4–10 days group by IgA kit were collected at the 4th day after illness onset, all other sera includes 2 at the 6th day, 3 at the 7th day, 1 at the 8th day, 6 at the 9th day, and 3 at 10th day after illness onset were tested as positive. In the group of 11–41 days after symptom onset, both RBD IgA and IgG kit showed the same positive diagnostic rate of 99.5% (198/199). In contrast, IgM kit somehow showed a relatively lower positive diagnostic rate as 98.5% (196/199). These results suggest that including IgA in a test provides better diagnostic outcome in early stages. Overall, the medium seroconversion time for IgA, IgM, and IgG are 4–6, 4–6, and 5–10 days post symptom onset, respectively, if tested with the RBD-kits described in this study. While it generally follows a typical seroconversion and immunoglobulin class switching time course, our kits provides an early diagnosis solution due to high sensitivities. To better understand the trends of antibody levels in all of the 87 COVID-19 patients (some of them contributed multiple samples), we plotted the median RLU reading according the time windows when sera were collected (Fig. 1e). IgA detection shows the highest sensitivity during about 4–25 days after illness onset. The median RLU of RBD-specific IgA reached the peak during 16–20 days after illness onset, and then began to decline but remained at relatively high reading until 31–41 days. The median RLU of RBD-specific IgG was the lowest in early disease stages but raised at 15 days post illness onset, the IgG reached its peak during 21–25 days after illness onset, and stayed at a relatively high reading until 31–41 days, suggesting that IgG is powerful for diagnostics at later stages. Although IgM reached its peak at early stages, the RLU reading was lower than that of IgA or IgG. We further divided the 87 patients into three severity groups based on established clinical classifications. Consistent with a previous report, 7 we found that COVID-19 severity is correlated positively with age in our cohort (Supplementary Fig. 3). Patients with severe symptoms were significantly older (median age of 62.5) than those patients with moderate (median age of 46) and mild symptoms (median age of 30), as expected. We used the data of antibody levels at the period of 16–25 days after illness onset, when all of the three isotypes reached or were near their peaks (Fig. 1e). If there were more than one data points, the average value was taken. Serum IgM and IgG levels in moderate and severe COVID-19 patients were significantly higher than mild cases, while no significant difference was observed between severe and moderate patients (Fig. 1g, h). However, we found that IgA levels in severe cases were significantly higher than those mild or moderate cases (Fig. 1f). The molecular mechanism of this observation warrants future studies. There are some limitations in this study at the current form. We used 216 serum samples from 87 confirmed COVID-19 patients in this study, and serum samples were not available every day for each patient. The earliest serum was collected at the 4th day, and last one was at the 41th day after self-reported illness onset. There are only 17 cases of serum samples collected within the first 10 days after illness onset; which consequently influenced the accuracy. Similarly, there were only 23 cases of serum samples taken after 30 days post illness onset, hampering an analysis of long-term antibody levels in recovered patients. We are currently following up some of the 87 convalescent COVID-19 patients who are willing to participate in further study. Nevertheless, this study provide valuable information regarding COVID-19 serological testing and seroconversion responses, especially for IgA antibodies. Supplementary information Supplemental materials
              Bookmark
              • Record: found
              • Abstract: found
              • Article: not found

              The regulation of IgA class switching.

              IgA class switching is the process whereby B cells acquire the expression of IgA, the most abundant antibody isotype in mucosal secretions. IgA class switching occurs via both T-cell-dependent and T-cell-independent pathways, and the antibody targets both pathogenic and commensal microorganisms. This Review describes recent advances indicating that innate immune recognition of microbial signatures at the epithelial-cell barrier is central to the selective induction of mucosal IgA class switching. In addition, the mechanisms of IgA class switching at follicular and extrafollicular sites within the mucosal environment are summarized. A better understanding of these mechanisms may help in the development of more effective mucosal vaccines.
                Bookmark

                Author and article information

                Contributors
                peiwwien@yahoo.com
                Journal
                J Med Virol
                J Med Virol
                10.1002/(ISSN)1096-9071
                JMV
                Journal of Medical Virology
                John Wiley and Sons Inc. (Hoboken )
                0146-6615
                1096-9071
                17 December 2020
                : 10.1002/jmv.26703
                Affiliations
                [ 1 ] Department of Laboratory Medicine The First People's Hospital of Jingmen Hubei China
                Author notes
                [*] [* ] Correspondence Pei Wang, Department of Laboratory Medicine, The First People's Hospital of Jingmen, Hubei, China.

                Email: peiwwien@ 123456yahoo.com .

                Author information
                http://orcid.org/0000-0002-0550-1029
                Article
                JMV26703
                10.1002/jmv.26703
                7753495
                33289143
                8a204086-9d3b-45c3-bce1-d2478582156a
                © 2020 Wiley Periodicals LLC

                This article is being made freely available through PubMed Central as part of the COVID-19 public health emergency response. It can be used for unrestricted research re-use and analysis in any form or by any means with acknowledgement of the original source, for the duration of the public health emergency.

                History
                : 20 September 2020
                : 17 November 2020
                : 28 November 2020
                Page count
                Figures: 0, Tables: 0, Pages: 2, Words: 1053
                Categories
                Letter to the Editor
                Letter to the Editor
                Custom metadata
                2.0
                corrected-proof
                Converter:WILEY_ML3GV2_TO_JATSPMC version:5.9.6 mode:remove_FC converted:22.12.2020

                Microbiology & Virology
                Microbiology & Virology

                Comments

                Comment on this article