Dual roles of CD40 on microbial containment and the development of immunopathology in response to persistent fungal infection in the lung.

Persistent pulmonary infection with Cryptococcus neoformans in C57BL/6 mice results in chronic inflammation that is characterized by an injurious Th2 immune response. In this study, we performed a comparative analysis of cryptococcal infection in wild-type versus CD40-deficient mice (in a C57BL/6 genetic background) to define two important roles of CD40 in the modulation of fungal clearance as well as Th2-mediated immunopathology. First, CD40 promoted microanatomic containment of the organism within the lung tissue. This protective effect was associated with: i) a late reduction in fungal burden within the lung; ii) a late accumulation of lung leukocytes, including macrophages, CD4+ T cells, and CD8+ T cells; iii) both early and late production of tumor necrosis factor-α and interferon-γ by lung leukocytes; and iv) early IFN-γ production at the site of T cell priming in the regional lymph nodes. In the absence of CD40, systemic cryptococcal dissemination was increased, and mice died of central nervous system infection. Second, CD40 promoted pathological changes in the airways, including intraluminal mucus production and subepithelial collagen deposition, but did not alter eosinophil recruitment or the alternative activation of lung macrophages. Collectively, these results demonstrate that CD40 helps limit progressive cryptococcal growth in the lung and protects against lethal central nervous system dissemination. CD40 also promotes some, but not all, elements of Th2-mediated immunopathology in response to persistent fungal infection in the lung.