CD40 Expression by B Cells Is Required for Optimal Immunity to Murine Pneumocystis Infection

Abstract

Abstract CD40–CD40 ligand interactions are critical for controlling Pneumocystis infection. However, which CD40-expressing cell populations are important for this interaction have not been well defined. We used a cohousing mouse model of Pneumocystis infection, combined with flow cytometry and quantitative polymerase chain reaction, to examine the ability of different populations of cells from C57BL/6 mice to reconstitute immunity in CD40 knockout mice. Unfractionated splenocytes, as well as purified B cells, were able to control Pneumocystis infection, while B cell–depleted splenocytes and unstimulated bone marrow–derived dendritic cells were unable to control infection in CD40 knockout mice. Pneumocystis antigen–pulsed bone marrow–derived dendritic cells showed early but limited control of infection. Additional findings were consistent with recent studies that suggested a role for antigen presentation by B cells; specifically, by using cells from immunized animals, B cells were able to present Pneumocystis antigens to induce proliferation of T cells. Thus, CD40 expression by B cells appears necessary for robust immunity to Pneumocystis.