Functional T cells in primary immune response to histoplasmosis

Abstract

Functional T cells are critical to host defense against infection. It has been reported that functional T cells as determined by their cytokine production represent antigen-specific T cells in infectious disease models. In this study, we enumerated Histoplasma-specific interferon γ-producing cells in bulk splenocyte culture and showed that infection with Histoplasma capsulatum, an intracellular pathogen of the macrophage, activated both CD4 and CD8 T cells. The magnitude of CD8 T cell response was lower than CD4 T cell, but the expansion and contraction of both cell types followed the same kinetics. Over 90% of interferon γ-producing CD4 T cells and >85% of CD8 T cells expressed CD44hi phenotype. The strong correlation between interferon γ production and CD44hi expression was observed not only at the peak of response but also throughout the course of infection. Moreover, a broad spectrum of Vβ populations responded to systemic as well as pulmonary infections, suggesting no obvious T cell receptor bias in primary immune response to histoplasmosis. While each Vβ population contributed to interferon γ production, several specific Vβ populations made up higher percentages of interferon γ-producing cells. Our study laid the groundwork for further investigations in immune response to histoplasmosis. © 2004 The Japanese Society for Immunology.