Antibody (IgA, IgG, and IgG Subtype) Responses to SARS-CoV-2 in Severe and Nonsevere COVID-19 Patients.

For the assessment of vaccine-induced immune response and to understand the role of antibodies in neutralization, it is necessary to assess dynamics of various antibodies in patients with different clinical manifestations. This study aims to quantitate circulating levels of IgA/IgG and IgG subtypes induced at different days postonset of symptoms, in severe and nonsevere patients. For this, serum or plasma samples (n = 146) collected from 79 COVID-19 patients were used. Indirect severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) specific IgA, IgG, and IgG subtype specific enzyme-linked immunosorbent assays (ELISAs) were performed. Antibody titers between severe and nonsevere patients were compared at different times postonset of clinical symptoms. Titers in ELISA were compared to neutralizing antibody (Nab) titers determined by plaque reduction neutralization test (PRNT). Over 75% patients were positive for IgA/IgG antibodies in the first week. The ELISA titers did not differ during the first week; however, severe disease exhibited raised titers thereafter. Nab titers correlated with the ELISA titers in mild presentation but not in severe disease. IgA and IgG1 antibodies correlated stronger with Nabs. The findings highlighted that IgA together with IgG play an important in SARS-CoV-2 neutralization. These results will prove useful in assessing efficacy of vaccines and understanding disease pathogenesis.

Standardization of ELISA for anti-chikungunya-IgG antibodies and age-stratified prevalence of anti-chikungunya-IgG antibodies in Pune, India.

Chikungunya (CHIKV) reemerged in India after a gap of 32 years, in 2005-2006 and has established endemicity in Pune. To assess the degree of CHIKV exposure, we estimated age-stratified prevalence of IgG antibodies to CHIKV in Pune population. This retrospective study utilized age-stratified serum samples collected from 15 wards of Pune in 2017 for dengue (DENV) virus study. Indirect anti-CHIKV-IgG ELISA was developed and used to test 1904 samples. Exposure to CHIKV and DENV was compared in the same population. CHIKV-specific plaque reduction neutralization test (PRNT) was employed to evaluate ELISA positivity and neutralizing potential of anti-CHIKV-IgG antibodies. Indirect ELISA showed 98.5% concordance with commercial ELISA. Seropositivity to CHIKV was 46.4%, one-third children < 15 years being antibody positive. A significant increase (45%, p = 0.026-0.038) was noted at 16-25 years and varied between 48 and 56% until the age 65. In elderly (65 + years), antibody positivity was reduced (41%, p = 0.01). In children, CHIKV-PRNT50 titers increased with age and remained comparable from the age group 11-15 until > 65. Exposure to DENV was higher than CHIKV. Lower exposure of children and elderly could be due to lesser exposure to the vectors. High prevalence of IgG antibodies needs to be addressed while planning vaccine studies for CHIKV.