DENV-specific IgA contributes protective and non-pathologic function during antibody-dependent enhancement of DENV infection.

Dengue represents a growing public health burden worldwide, accounting for approximately 100 million symptomatic cases and tens of thousands of fatalities yearly. Prior infection with one serotype of dengue virus (DENV) is the greatest known risk factor for severe disease upon secondary infection with a heterologous serotype, a risk which increases as serotypes co-circulate in endemic regions. This disease risk is thought to be mediated by IgG-isotype antibodies raised during a primary infection, which poorly neutralize heterologous DENV serotypes and instead opsonize virions for uptake by FcγR-bearing cells. This antibody-dependent enhancement (ADE) of infection leads to a larger proportion of susceptible cells infected, higher viremia and greater immunopathology. We have previously characterized the induction of a serum IgA response, along with the typical IgM and IgG responses, during dengue infection, and have shown that DENV-reactive IgA can neutralize DENV and competitively antagonize IgG-mediated ADE. Here, we evaluate the potential for IgA itself to cause ADE. We show that IgG, but not IgA, mediated ADE of infection in cells expressing both FcαR and FcγRs. IgG-mediated ADE stimulated significantly higher pro-inflammatory cytokine production by primary human macrophages, while IgA did not affect, or slightly suppressed, this production. Mechanistically, we show that DENV/IgG immune complexes bind susceptible cells significantly more efficiently than DENV/IgA complexes or virus alone. Finally, we show that over the course of primary dengue infection, the expression of FcγRI (CD64) increases during the period of acute viremia, while FcγRIIa (CD32) and FcαR (CD89) expression decreases, thereby further limiting the ability of IgA to facilitate ADE in the presence of DENV. Overall, these data illustrate the distinct protective role of IgA during ADE of dengue infection and highlight the potential therapeutic and prognostic value of DENV-specific IgA.

Soluble NS1 Antagonizes IgG- and IgA- Mediated Monocytic Phagocytosis of DENV Infected Cells.

Dengue virus (DENV) is endemic in >100 countries, infecting an estimated 400 million individuals every year. Infection with DENV raises an antibody response primarily targeting viral structural proteins. However, DENV encodes several immunogenic nonstructural (NS) proteins, one of which, NS1, is expressed on the membrane of DENV-infected cells. IgG and IgA isotype antibodies that bind NS1 are abundant in serum following DENV infection. Our study aimed to determine if NS1-binding IgG and IgA isotype antibodies contribute to the clearance of DENV-infected cells by antibody-mediated cellular phagocytosis. We observed that both IgG and IgA isotype antibodies can facilitate monocytic uptake of DENV NS1-expressing cells in an FcγRI- and FcαRI-dependent fashion. Interestingly, this process was antagonized by the presence of soluble NS1, suggesting that the production of soluble NS1 by infected cells may serve as immunological chaff, antagonizing opsonization and clearance of DENV-infected cells.

Evolution of inflammation and immunity in a dengue virus 1 human infection model.

Dengue virus (DENV) infections are major causes of morbidity and mortality throughout the tropics and subtropics. More than 400 million infections are estimated to occur every year, resulting in nearly 100 million symptomatic infections and more than 20,000 deaths. Early immune response kinetics to infection remain unclear, in large part due to the variable incubation period exhibited by the DENVs after introduction into a susceptible host. To fill this knowledge gap, we performed a comprehensive virologic and immunologic analysis of individuals experimentally infected with the underattenuated DENV-1 strain 45AZ5. This analysis captured both the kinetics and composition of the innate, humoral, and cellular immune responses elicited by experimental DENV-1 infection, as well as virologic and clinical features. We observed a robust DENV-specific immunoglobulin A (IgA) antibody response that manifested between the appearance of DENV-specific IgM and IgG in all challenged individuals, as well as the presence of a non-neutralizing/NS1-specific antibody response that was delayed relative to the appearance of DENV virion-specific humoral immunity. RNA sequencing analysis revealed discrete and temporally restricted gene modules that correlated with acute viremia and the induction of adaptive immunity. Our analysis provides a detailed description, in time and space, of the evolving matrix of DENV-elicited human inflammation and immunity and reveals several previously unappreciated immunological aspects of primary DENV-1 infection that can inform countermeasure development and evaluation.

Simultaneous analysis of antigen-specific B and T cells after SARS-CoV-2 infection and vaccination.

Conventional methods for quantifying and phenotyping antigen-specific lymphocytes can rapidly deplete irreplaceable specimens. This is due to the fact that antigen-specific T and B cells have historically been analyzed in independent assays each requiring millions of cells. A technique that facilitates the simultaneous detection of antigen-specific T and B cells would allow for more thorough immune profiling with significantly reduced sample requirements. To this end, we developed the B and T cell tandem lymphocyte evaluation (BATTLE) assay, which allows for the simultaneous identification of SARS-CoV-2 Spike reactive T and B cells using an activation induced marker (AIM) T cell assay and dual-color B cell antigen probes. Using this assay, we demonstrate that antigen-specific B and T cell subsets can be identified simultaneously using conventional flow cytometry platforms and provide insight into the differential effects of mRNA vaccination on B and T cell populations following natural SARS-CoV-2 infection.