CD4 and X-linked hyper-IgM syndrome: Defects in the CD40 pathway are relevant to at least 3 groups of patients that develop ocular and/or cerebral toxoplasmosis: patients with X-linked Hyper IgM syndrome who lack functional CD154 [52], newborns since neonatal CD4+ T cells exhibit impaired expression of CD154 [53], [54] and CD40 levels are reduced on neonatal dendritic cells [54], and HIV-1+ patients because they exhibit a defect in CD154 induction in their CD4+ T cells [55], [56].