Background While convalescent plasma (CP) may benefit patients with COVID‐19, fundamental questions remain regarding its efficacy, including the components of CP that may contribute to its therapeutic effect. Most current serological evaluation of CP relies on examination of total immunoglobulin or IgG‐specific anti‐SARS‐CoV‐2 antibody levels. However, IgA antibodies, which also circulate and are secreted along the respiratory mucosa, represent a relatively uncharacterized component of CP. Study design and methods Residual samples from patients and CP donors were assessed for IgM, IgG, and IgA anti‐SARS‐CoV‐2 antibody titers against the receptor‐binding domain responsible for viral entry. Symptom onset was obtained by chart review. Results Increased IgA anti‐SARS‐CoV‐2 antibody levels correlated with clinical improvement and viral clearance in an infant with COVID‐19, prompting a broader examination of IgA levels among CP donors and hospitalized patients. Significant heterogeneity in IgA levels was observed among CP donors, which correlated weakly with IgG levels or the results of a commonly employed serological test. Unlike IgG and IgM, IgA levels were also more likely to be variable in hospitalized patients and this variability persisted in some patients >14 days following symptom onset. IgA levels were also less likely to be sustained than IgG levels following subsequent CP donation. Conclusions IgA levels can be very heterogenous among CP donors and hospitalized patients and do not necessarily correlate with commonly employed testing platforms. Examining isotype levels in CP and COVID‐19 patients may allow for a tailored approach when seeking to fill specific gaps in humoral immunity.

Accurate diagnosis of acute severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) infection is critical for appropriate management of patients with this disease. We examined the possible complementary role of lab developed class-specific clinical serology in assessing SARS-CoV-2 infection in hospitalized patients. Serological tests for IgG, IgA, and IgM antibodies against the receptor binding domain (RBD) of SARS-CoV-2 were evaluated using samples from real time RT PCR (qRT-PCR)-confirmed in-patient COVID-19 cases. We analyzed the influence of timing and clinical severity on the diagnostic value of class-specific coronavirus disease 2019 (COVID-19) serology testing. Cross-sectional analysis revealed a higher sensitivity and specificity at lower optical density cutoffs for IgA in hospitalized patients when compared to IgG and IgM serology (IgG area under the curve (AUC): 0.91; 95%CI 0.89 to 0.93 vs. IgA AUC: 0.97; 95% CI 0.96 to 0.98 vs. IgM AUC: 0.95; 95% CI 0.92 to 0.97). The enhanced performance of IgA serology was apparent in the first two weeks after symptom onset and the first week after PCR testing. In patients requiring intubation, all three tests exhibit enhanced sensitivity. Among PCR-negative patients under investigation for SARS-CoV-2 infection 2 out of 61 showed clear evidence of seroconversion IgG, IgA and IgM. Suspected false-positive results in the latter population were most frequently observed in IgG and IgM serology tests. Our findings suggest the potential utility of IgA serology in the acute setting and explore the benefits and limitations of class-specific serology as a complementary diagnostic tool to PCR for COVID-19 in the acute setting.

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Background & Aims The intestinal epithelium must be resilient to physiochemical stress to uphold the physiological barrier separating the systemic compartment from the microbial and antigenic components of the gut lumen. Identifying proteins that mediate protection and enhancing their expression is therefore a clear approach to promote intestinal health. We previously reported that oral ingestion of the probiotic Lactobacillus rhamnosus GG not only induced the expression of several recognized cytoprotective factors in the murine colon, but also many genes with no previously described function, including the gene encoding proline-rich acidic protein 1 (PRAP1). PRAP1 is a highly expressed protein in the epithelium of the gastrointestinal tract and we sought to define its function in this tissue. Methods Purified preparations of recombinant PRAP1 were analyzed biochemically and PRAP1 antisera were used to visualize localization in tissues. Prap1 -/- mice were characterized at baseline and challenged with total body irradiation, then enteroids were generated to recapitulate the irradiation challenge ex vivo. Results PRAP1 is a 17-kilodalton intrinsically disordered protein with no recognizable sequence homology. PRAP1 expression levels were high in the epithelia of the small intestine. Although Prap1 -/- mice presented only mild phenotypes at baseline, they were highly susceptible to intestinal injury upon challenge. After irradiation, the Prap1 -/- mice showed accelerated death with a significant increase in apoptosis and p21 expression in the small intestinal epithelium. Conclusions PRAP1 is an intrinsically disordered protein highly expressed by the gastrointestinal epithelium and functions at exposed surfaces to protect the barrier from oxidative insult.

Objectives: Examine possible pooling strategies designed to expand SARS-CoV-2 serological testing capacity. Methods: Negative pools were assessed to determine optimal optical density (OD) cutoffs, followed by spiking weak or strong positive samples to assess initial assay performance. Samples were then randomly subjected to pool and individual testing approaches. Results: Single positive specimens consistently converted pools of 5, 10, or 20 into positive outcomes. However, weaker IgG-positive samples failed to similarly convert pools of 50 to a positive result. In contrast, a stronger individual positive sample converted all pools tested into positive outcomes. Finally, examination of 150 samples configured into pools of 5, 10, 20 or 50 accurately predicted the presence of positive or negative specimens within each pool. Conclusions: These results suggest that pooling strategies may allow expansion of serological testing capacity. While limitations exist, such strategies may aid in large-scale epidemiological screening or identification of optimal convalescent plasma donors.