Type I Interferons Induce T Regulatory 1 Responses and Restrict Humoral Immunity during Experimental Malaria.

CD4 T cell-dependent antibody responses are essential for limiting Plasmodium parasite replication and the severity of malaria; however, the factors that regulate humoral immunity during highly inflammatory, Th1-biased systemic infections are poorly understood. Using genetic and biochemical approaches, we show that Plasmodium infection-induced type I interferons limit T follicular helper accumulation and constrain anti-malarial humoral immunity. Mechanistically we show that CD4 T cell-intrinsic type I interferon signaling induces T-bet and Blimp-1 expression, thereby promoting T regulatory 1 responses. We further show that the secreted effector cytokines of T regulatory 1 cells, IL-10 and IFN-γ, collaborate to restrict T follicular helper accumulation, limit parasite-specific antibody responses, and diminish parasite control. This circuit of interferon-mediated Blimp-1 induction is also operational during chronic virus infection and can occur independently of IL-2 signaling. Thus, type I interferon-mediated induction of Blimp-1 and subsequent expansion of T regulatory 1 cells represent generalizable features of systemic, inflammatory Th1-biased viral and parasitic infections that are associated with suppression of humoral immunity.

Discrimination of Jamaican fruit bat lymphocytes by flow cytometry.

Bats are natural reservoir hosts of many important zoonotic viruses but because there are few immunological reagents and breeding colonies available for infectious disease research, little is known about their immune responses to infection. We established a breeding colony Jamaican fruit bats ( Artibeus jamaicensis ) to study bat virology and immunology. The species is used as a natural reservoir model for H18N11 influenza A virus, and as a surrogate model for SARS-CoV-2, MERS-CoV and Tacaribe virus. As part of our ongoing efforts to develop this model organism, we sought to identify commercially available monoclonal antibodies (mAb) for profiling Jamaican fruit bat lymphocytes. We identified several cross-reactive mAb that can be used to identify T and B cells; however, we were unable to identify mAb for three informative T cell markers, CD3γ, CD4 and CD8α. We targeted these markers for the generation of hybridomas, and identified several clones to each that can be used with flow cytometry and fluorescence microscopy. Specificity of the monoclonal antibodies was validated by sorting lymphocytes, followed by PCR identification of confirmatory transcripts. Spleens of Jamaican fruit bats possess about half the number of T cells than do human or mouse spleens, and we identified an unusual population of cells that expressed the B cell marker CD19 and the T cell marker CD3. The availability of these monoclonal antibodies will permit a more thorough examination of adaptive immune responses in Jamaican fruit bats that should help clarify how the bats control viral infections and without disease. Importance: Bats naturally host a number of viruses without disease, but which can cause significant disease in humans. Virtually nothing is known about adaptive immune responses in bats because of a lack of immunological tools to examine such responses. We have begun to address this deficiency by identifying several commercially available monoclonal antibodies to human and mouse antigens that are cross-reactive to Jamaican fruit bat lymphocyte orthologs. We also generated monoclonal antibodies to Jamaican fruit bat CD3γ, CD4 and CD8α that are suitable for identifying T cell subsets by flow cytometry and immunofluorescent staining of fixed tissues. Together, these reagents will allow a more detailed examination of lymphocyte populations in Jamaican fruit bats.