Natural Killer T Cells Are Critical for Dendritic Cells to Induce Immunity in Chlamydial Pneumonia

Rationale: We previously showed an important role of natural killer T cells (NKT) in skewing the adaptive T cell immunity to Chlamydia pneumoniae (Cpn), an intracellular bacterial lung infection, but the mechanism remains unclear.Objectives: To investigate the underlying mechanism by which NKT modulate T cell responses in chlamydial pneumonia.Methods: We examined the effect of NKT activation in modulating DC function, especially in generating protective immunity against Cpn infection using combination of NKT knockout (KO) mice and specific NKT activation approaches.Measurements and Main Results: We found that NKT activation in vivo after Cpn infection induces phenotypic and functional changes in dendritic cells (DC). DC from NKT-deficient mice showed reduced CD40 expression and IL-12 production, whereas enhancing NKT activation using α-GalCer increased CD40 expression and IL-12 production. Co-culture of DC with NKT enhanced bioactive IL-12p70 production by DC in a CD40L-, IFN-γ–, and cell–cell contact–dep...