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Understanding humoral responses to SARS-CoV-2 is critical for improving diagnostics, therapeutics, and vaccines. Deep serological profiling of 232 COVID-19 patients and 190 pre-COVID-19 era controls using VirScan revealed over 800 epitopes in the SARS-CoV-2 proteome, including 10 epitopes likely recognized by neutralizing antibodies. Pre-existing antibodies in controls recognized SARS-CoV-2 ORF1, while only COVID-19 patients primarily recognized spike and nucleoprotein. A machine learning model trained on VirScan data predicted SARS-CoV-2 exposure history with 99% sensitivity and 98% specificity; a rapid Luminex-based diagnostic was developed from the most discriminatory SARS-CoV-2 peptides. Individuals with more severe COVID-19 exhibited stronger and broader SARS-CoV-2 responses, weaker antibody responses to prior infections, and higher incidence of CMV and HSV-1, possibly influenced by demographic covariates. Among hospitalized patients, males make greater SARS-CoV-2 antibody responses than females.

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Humoral responses in coronavirus disease 2019 (COVID-19) are often of limited durability, as seen with other human coronavirus epidemics. To address the underlying etiology, we examined post mortem thoracic lymph nodes and spleens in acute SARS-CoV-2 infection and observed the absence of germinal centers and a striking reduction in Bcl-6 + germinal center B cells but preservation of AID + B cells. Absence of germinal centers correlated with an early specific block in Bcl-6 + T FH cell differentiation together with an increase in T-bet + T H1 cells and aberrant extra-follicular TNF-α accumulation. Parallel peripheral blood studies revealed loss of transitional and follicular B cells in severe disease and accumulation of SARS-CoV-2-specific “disease-related” B cell populations. These data identify defective Bcl-6 + T FH cell generation and dysregulated humoral immune induction early in COVID-19 disease, providing a mechanistic explanation for the limited durability of antibody responses in coronavirus infections, and suggest that achieving herd immunity through natural infection may be difficult.

The relationship between SARS-CoV-2 viral load and risk of disease progression remains largely undefined in coronavirus disease 2019 (COVID-19). Here, we quantify SARS-CoV-2 viral load from participants with a diverse range of COVID-19 disease severity, including those requiring hospitalization, outpatients with mild disease, and individuals with resolved infection. We detected SARS-CoV-2 plasma RNA in 27% of hospitalized participants, and 13% of outpatients diagnosed with COVID-19. Amongst the participants hospitalized with COVID-19, we report that a higher prevalence of detectable SARS-CoV-2 plasma viral load is associated with worse respiratory disease severity, lower absolute lymphocyte counts, and increased markers of inflammation, including C-reactive protein and IL-6. SARS-CoV-2 viral loads, especially plasma viremia, are associated with increased risk of mortality. Our data show that SARS-CoV-2 viral loads may aid in the risk stratification of patients with COVID-19, and therefore its role in disease pathogenesis should be further explored.

Purpose IgG4-related disease (IgG4-RD) is an immune-mediated fibroinflammatory condition that can affect nearly any organ. No detailed clinical and laboratory assessments have been reported in large numbers of patients with IgG4-RD diagnoses established by strict clinicopathological correlation. Methods We reviewed the baseline features of 125 patients with biopsy-proven disease. The diagnosis was confirmed by pathology review according to consensus diagnostic criteria. Disease activity and damage were assessed by the IgG4-RD Responder Index (RI). Flow cytometry was used to assess levels of circulating plasmablasts. Results Of the 125 patients, 103 had active disease and 86 were on no treatment. Only 51% of the patients with active disease had elevated serum IgG4 concentrations. However, patients with active disease and elevated serum IgG4 concentrations were older, had a higher RI, a greater number of organs involved, lower complement levels, higher absolute eosinophil counts, and higher IgE levels compared to those with active disease but normal serum IgG4 (P<0.01 for all comparisons). The correlation between IgG4+ plasmablast level and RI (R=0.45, P=0.003) was stronger than that of total plasmablasts and RI. Seventy-six (61%) of the patients were male, but no significant differences according to gender were observed with regard to disease severity, organ involvement, or serum IgG4 concentrations. Glucocorticoids failed to produce sustained remission in the majority of patients. Conclusion Nearly 50% of this patient cohort with biopsy-proven, clinically-active IgG4-RD had normal serum IgG4 concentrations. Serum IgG4 elevation identify a subset with more inflammatory features. IgG4+ plasmablasts correlate well with disease activity.

Bone marrow-derived B cells make an important cell fate choice to develop into either follicular B cells or marginal zone B cells in the spleen, which depends on signalling through the B cell receptor, Notch2, the receptor for B cell-activating factor and the canonical nuclear factor-kappaB pathway, as well as signals involved in the migration and anatomical retention of marginal zone B cells. Recent information discussed in this Review reconciles some of the controversies regarding the role of the B cell receptor in this cell fate decision and a clearer picture has also emerged regarding the anatomical location of ligands for Notch2 in the spleen. This cell fate decision could provide mechanistic insights that are relevant to other commitment events in lymphocytes.