Distinct Compartmentalization of CD4+ T-Cell Effector Function Versus Proliferative Capacity during Pulmonary Cryptococcosis

The activation and expansion of T cells and their acquisition of effector function are key steps in the development of the adaptive immune response. Most infections are predominantly outside of the lymphoid tissues, and it is unclear at what point developmentally and anatomically T cells acquire effector function in vivo. In these studies, we compared the activation and polarization of T cells during murine pulmonary Cryptococcus neoformans infection in the secondary lymphoid tissues and at the site of primary infection. Few CD4+ and CD8+ T cells expressed an activated phenotype (CD44hi, CD25+, CD69+, CD62Llo, CD45RBlo) at the sites of clonal expansion (lymph nodes, spleen, and blood). In contrast, a high percentage of T cells expressed activation markers at the site of primary infection, the lungs. Additionally, the polarization of CD4+ T cells to interferon-γ-producing effector cells occurred at the site of infection, the lungs. CD4+ and CD8+ T cells from secondary lymphoid organs responded to TCR restimulation by proliferating, whereas T cells from the lungs proliferated poorly. This report demonstrates for the first time that T-cell activation and effector function in secondary lymphoid tissues during fungal infection is characteristically different from that at the site of primary infection.