Specific T cell repertoires mediate protective immunity to Histoplasma capsulatum

Histoplasma capsulatum (Hc) is a dimorphic fungus that causes a wide spectrum of disease. The interaction of T cells with macrophages and the subsequent production of cytokines are essential for protection. This thesis examines the importance of the T cell receptor (TCR) repertoire during the generation of immunity to infection with Hc and vaccination with a protective antigen (Ag). During primary infection, Vβ4 + T cells expand in the lungs and depletion of these cells increases the fungal burden in mice. To examine the Ag-specificity of lung Vβ4 + cells, they were isolated from infected mice and used to generate hybridomas. These cells were screened for Ag reactivity using an extract derived from the cell wall and cell membrane of Hc yeast. T cell immunoblotting with hybridomas indicate that the majority of lung-derived cells respond with an antigen at 110–130 kDA. Mass spectrometry identified this antigen as a homolog of Sec31 from Saccharomyces cerevisiae. In parallel, we examined the TCR repertoire following immunization with the protective Ag, Hsp60. A majority of T cell clones derived from Hsp60 immunized mice expressed Vβ8.1/8.2. Depletion of Vβ8.1/8.2+ cells abrogated the efficacy of Hsp60 immunization. Among these cells, those that generate IFN-γ and reacted to F3 were able to confer protection in IFN-γ −/− and TCRα/β−/− mice. The protective response to Hsp60 also relies on the presence of IL-10, IL-12, and IFN-γ. To determine if the absence of IL-10 and IFN-γ disrupt the generation of immunity to Hsp60 by altering the TCR repertoire, T cells were isolated from IL-10 and IFN-γ deficient mice following immunization with Hsp60. The IL-10−/−-derived TCR repertoire resembled that previously observed in wildtype animals, while IFN-γ −/− repertoire had a smaller proportion of Vβ8.18/2 + cells. Together, the data presented here demonstrate that specific subsets of Ag-specific T cells mediate the protective response to Hc during both the respond to primary infection as well as the challenge subsequent to vaccination. The activity of these cells is associated with production of IFN-γ, which also influences the repertoire during initial stages of the immune response.