CD4 and infection: Effective clearance of T. pallidum at sites of infection occurs through the induction of a delayed-type hypersensitivity (DTH) response, which is mediated by the infiltration of CD4+ T cells and the activation of macrophages to phagocytose and kill T. pallidum (Baker-Zander and Lukehart, 1992; Carlson et al., 2011).