There are several players of the innate and adaptive immune system that participate in clearance of infection, however it is well established that γ-IFN secretion by CD4+ Th1 cells is, (i) the primary requisite to elicit protection against C. muridarum (Perry et al., 1997; Li et al., 2008; Gondek et al., 2009; Darville and Hiltke, 2010), and (ii) a major, but not categorical, player in adaptive immunity against C. trachomatis (Morrison et al., 2011). The gene discussed is CD4; the disease is infection.