CD4⁺ T cell expression of MyD88 is essential for normal resolution of chlamydia muridarum genital tract infection

Resolution ofChlamydiagenital tract infection is delayed in the absence of MyD88. In these studies, we first used bone marrow chimeras to demonstrate a requirement for MyD88 expression by hematopoietic cells in the presence of a wild-type epithelium. Using mixed bone marrow chimeras we then determined that MyD88 expression was specifically required in the adaptive immune compartment. Furthermore, adoptive transfer experiments revealed that CD4⁺ T cell expression of MyD88 was necessary for normal resolution of genital tract infection. This requirement was associated with a reduced ability of MyD88 ^-/- CD4⁺ T cells to accumulate in the draining lymph nodes and genital tract when exposed to the same inflammatory milieu as wild-type CD4⁺ T cells. We also demonstrated that the impaired infection control we observed in the absence of MyD88 could not be recapitulated by deficiencies in TLR or IL-1R signaling. In vitro, we detected an increased frequency of apoptotic MyD88^-/- CD4⁺ T cells upon activation in the absence of exogenous ligands for receptors upstream of MyD88. These data reveal an intrinsic requirement for MyD88 in CD4⁺ T cells duringChlamydiainfection and indicate that the importance of MyD88 extends beyond innate immune responses by directly influencing adaptive immunity.