CD4 and infection: It is likely that IL-10 production by Th1 cells is evoked under conditions of high inflammation and antigenic stimulation, whereas regulatory CD4+ T cells producing IL-10 may operate to regulate the immune response under conditions in which the pathogen is clinically controlled, such as in infection with L. major (Friedlin strain) (Belkaid et al., 2002; Suffia et al., 2006).