Serological assays to measure dimeric IgA antibodies in SARS‐CoV‐2 infections

Abstract

Current serological tests cannot differentiate between total immunoglobulin A (IgA) and dimeric IgA (dIgA) associated with mucosal immunity. Here, we describe two new assays, dIgA‐ELISA and dIgA‐multiplex bead assay (MBA), that utilize the preferential binding of dIgA to a chimeric form of secretory component, allowing the differentiation between dIgA and monomeric IgA. dIgA responses elicited through severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) infection were measured in (i) a longitudinal panel, consisting of 74 samples (n = 20 individuals) from hospitalized cases of coronavirus disease 2019 (COVID‐19); (ii) a longitudinal panel, consisting of 96 samples (n = 10 individuals) from individuals with mild COVID‐19; (iii) a cross‐sectional panel with PCR‐confirmed SARS‐CoV‐2 infection with mild COVID‐19 (n = 199) and (iv) pre–COVID‐19 samples (n = 200). The dIgA‐ELISA and dIgA‐MBA demonstrated a specificity for dIgA of 99% and 98.5%, respectively. Analysis of dIgA responses in the longitudinal panels revealed that 70% (ELISA) and 50% (MBA) of patients elicited a dIgA response by day 20 after PCR diagnosis with a SARS‐CoV‐2 infection. Individuals with mild COVID‐19 displayed increased levels of dIgA within the first 3 weeks after diagnosis but responses appeared to be short lived, compared with sustained IgA levels. However, in samples from hospitalized patients with COVID‐19 we observed high and sustained levels of dIgA, up to 245 days after PCR diagnosis. Our results suggest that severe COVID‐19 infections are associated with sustained levels of plasma dIgA compared with mild cases.

Dimeric immunoglobulin A as a novel diagnostic marker of measles infection

“…Using an in-house indirect ELISA protocol for dIgA detection (18) on in-house pre-coated VL antigen plates and commercial plates, we observed the presence of anti-measles VL dIgA in levels as comparably high as IgM in two independent panels of confirmed acute measles serum/plasma samples (Figure 1, 2). Although the distribution of anti-measles VL dIgA in measles samples was significantly higher than non-measles controls on both in-house pre-coated antigen plates and Euroimmun pre-coated antigen plates, the reactivity of measles samples in the latter was much lower.…”

“…IgM ELISAs were performed according to manufacturers' protocols. For detection of anti-measles dIgA, in-house lyophilized chimeric secretory component (cSC) protein and anti-secretory component (anti-SC) antibody as previously described (17,18) were used in an indirect ELISA. Briefly, strips prepared in-house and commercial pre-coated antigen strips (Euroimmun/Euroimmun NP kits) were blocked with 1.5% bovine serum albumin for 1 hour at 37°C in a humidified environment.…”

“…Longitudinal observations in patients with hepatitis C and COVID-19 suggest that dIgA from natural infection is transiently detectable in blood from 7 - 100 days (16, 17). In particular, data from a prospective study of dIgA response in COVID-19 suggest that dIgA from natural infection is transiently detectable from 7 - 100 days (∼14 weeks), and unlike IgG and IgA responses which are sustained (18).…”

Dimeric immunoglobulin A as a novel diagnostic marker of measles infection

“…For detection of anti-measles dIgA, in-house lyophilized chimeric secretory component (cSC) protein and anti-secretory component (anti-SC) antibody as previously described ( 17 , 18 ) were used in an indirect ELISA. Briefly, strips prepared in-house and commercial pre-coated antigen strips (Euroimmun/Euroimmun NP kits) were blocked with 1.5% bovine serum albumin for 1 h at 37°C in a humidified environment.…”

“…Longitudinal observations in patients with hepatitis C and COVID-19 suggest that dIgA from natural infection is transiently detectable in blood from 7 to 100 days ( 16 , 17 ). In particular, data from a prospective study of dIgA responses in COVID-19 suggest that dIgA from natural infection is transiently detectable from 7 to 100 days (~14 weeks), unlike IgG and IgA responses, which are sustained ( 18 ).…”