infection in mice, and specifically IFNγ-producing CD4 T helper-1 cells (Th1) have shown to be essential for protection.6,9 In line with the animal studies, C.t.-specific CD4 T cell responses is associated with protection against Chlamydia reinfection in women.10,11 Th17 T cells have also been observed during the course of a C.t. The gene discussed is CD4; the disease is infection.