Modulating T Follicular Cells In Vivo Enhances Antigen-Specific Humoral Immunity

Key Points Extended ABX treatment yielded higher affinity IgG following immunization. Extended ABX treatment resulted in enhanced pathology in a nephrotoxic nephritis model. PD-1 blockade phenocopied extended ABX following immunizations. Generation of high-affinity IgG is essential for defense against infections and cancer, which is the intended consequence of many vaccines, but can cause autoimmune and inflammatory diseases when inappropriately directed against self. The interplay of T follicular helper (TFH) cells and T follicular regulatory (TFR) cells is critical for the production of high-affinity IgG of a specific subclass. In this study, we sought to improve Ag-specific IgG responses with two interventions intended to transiently diminish TFR cell influence. First, adult mice were administered an antibiotic mixture (ABX) for an extended period to deplete the immunoregulatory intestinal microbiota. This intriguingly increased TFH cell and reduced TFR cell numbers. 2,4,6-Trinitrophenyl hapten conjugated to keyhole limpet hemocyanin immunization resulted in higher affinity 2,4,6-trinitrophenyl hapten–specific IgG1 in ABX mice compared with controls. In a model of IgG-driven inflammatory nephritis, ABX mice had significantly worse nephritis accompanied by higher affinity Ag-specific IgG2b and enriched TFH cells compared with controls. Second, we sought to functionally manipulate TFH and TFR cells, which both express the checkpoint inhibitory molecule, PD-1, by administration of anti–PD-1 during immunization. This intervention enhanced the affinity of Ag-specific IgG of the appropriate subclass and increased in TFH cells following 2,4,6-trinitrophenyl hapten conjugated to keyhole limpet hemocyanin immunization and nephritis induction. These results suggest that altering TFH and TFR cell ratios during immunization is an appealing strategy to qualitatively improve Ag- and subclass-specific IgG responses.