The purpose of this study is to evaluate the impression of IgG and IgM antibodies in autoimmune v/s severe COVID-19 infection. The objectives were to compare the levels of IgG and IgM antibodies in autoimmune and COVID-19 infection and to study the relationship between the duration of disease and levels of IgG and IgM. It was a retrospective observational study, carried out in inpatient wards of Continental Hospitals, Hyderabad, for a period of 6 months. The laboratory parameters and pharmacotherapy details were collected in the pre-designed annexure form. This observational retrospective study was done among 67 patients in tertiary care hospital in Hyderabad. In this study, the total study population was divided into two groups –Patients diagnosed with at least one autoimmune disease (Group I). Patients were diagnosed with Severe COVID-19 infection in our study (Group II). Infants and neonates are excluded from our study. a significant difference was seen in the mean of IgG between group I and group II patients. The IgG levels were found to be significantly higher in autoimmune diseases when compared with that of severe covid-19 infections. A significant difference was seen in the mean of IgM between group I and group II patients. IgM levels were found to be significantly higher in autoimmune diseases when compared with that of severe COVID-19. We conclude that autoimmune diseases are more prevalent in women of childbearing age. IgG and IgM levels were found to be increased with an increase in severity in both autoimmune disease and coronavirus disease. Hence, IgG and IgM antibody test may be useful as effective predictors in diagnosis and severity of autoimmune disease and severe coronavirus disease.
Autoimmune, Covid-19, SLE, RA, IgM, IgG, Immune system.
Autoimmune diseases are the third most common illness category, after cancer and heart disease, affecting approximately 8% of the population (1,2). Previously, autoimmune diseases were considered to be rare but, through rigorous epidemiological studies, have now been shown to affect 3–5% of the population, with autoimmune thyroid disease and type I diabetes (T1D) being the most common autoimmune diseases. There are nearly 100 types of autoimmune diseases causing various types of immunological dysfunction, some of which affect just one organ, such as primary biliary cirrhosis (PBC), and some of which affect multiple organ systems, such as systemic lupus erythematosus (SLE) (3). In the United States, autoimmune diseases are among the leading causes of death in young and middle-aged women (4).
Women are more prone to autoimmune diseases than men, with a female-to-male ratio of approximately 10:1 to 1:1 [except Crohn’s disease, with a ratio of 1:1.2] (5). A number of differences have been reported between countries and ethnic groups that live in the same area and are at risk of specific autoimmune diseases. However, the pattern may not be consistent across autoimmune diseases. Certain ethnic groups might have a higher risk for some autoimmune diseases, while others may have a lower risk (6). Natural polyreactive monoclonal antibodies (autoantibodies), which are derived from healthy subjects, bind to different antigens in a dose-saturable manner and to varying degrees (7). These antibodies bind different antigens based on two types of epitope recognition (8,9), i.e., Recognition of the same or similar epitopes within the context of different antigens, or Recognition of different epitopes within the context of different antigens. The majority of natural autoantibodies are produced by (CD5+) B-1 cells. These B-1 cells exhibit enhanced antigen presentation ability (10) and play an important role in the production of pathogenic autoantibodies in rheumatoid arthritis, Sjogren's syndrome, primary antiphospholipid syndrome, and systemic lupus (11). Eighty percent of patients with active SLE have antibodies directed against dsDNA (12). IgG antibodies are quite specific for SLE and are thus being used as diagnostic markers (13,14). Although there is much information regarding IgG in the pathogenesis of SLE, the role of IgM antibodies is less established (15).
Studies showed that IgM antibodies against dsDNA were common in SLE, as well as in rheumatoid arthritis, Sjogren’s syndrome, and autoimmune liver diseases (16). In normal adult murine or human serum, IgG natural antibodies can be observed when serum IgM has been removed or diluted (17-20). A pathogenic IgG autoantibody induces a compensatory increase in IgM antibodies (21). Pathogenic mechanisms unique to autoimmunity include antibodies against cell surface receptors that affect their function (i.e., myasthenia gravis), while in other autoimmune diseases, we can identify the same mechanisms involved in microbial defense (i.e., cell surface binding and lysis) (22). Any time an antibody responds to a soluble antigen, immune complexes are produced and cleared from the circulation by monocyte phagocytes (23). The deposition of the immune complex in the tissue as a cause of tissue damage is a common factor in SLE (24).
In COVID-19 infection, there is an increase in virus-specific IgM during the acute phase, followed by an increase in virus-specific IgG later on (25). In most of the patients, after 10 days of onset of symptoms, IgG or IgM antibody levels against SARS-CoV-2 nucleoprotein (NP) or receptor-binding domain (RBD) increased (26). Another study found that SARS-CoV-2 virus-specific IgG peaked 17–19 days after the onset of symptoms, while virus-specific IgM peaked 20–22 days after the onset of symptoms. Another interesting observation was that the IgG and IgM levels in critically ill patients were higher than in mildly ill patients. Most severely ill patients showed cytokine storms, which are marked by high levels of pro-inflammatory cytokines in the serum. Additionally, IgG, IgM, and IgA-specific antibodies against SARS-CoV-2. In COVID-19, high levels of acute phase reactants correlate with more severe disease (27). In outpatient and inpatient settings, ESR is the most commonly used laboratory test. In this study, we aimed to investigate the prevalence of autoimmune diseases and compare the roles of IgG and IgM in autoimmune diseases and severe covid-19 infection.
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