CTLA4 and infection: Using this prevalence as a guide, we therefore studied the infection history and measured the humoral immune response in CTLA4 mutation carriers against the following infectious agents: EBV (seroprevalence 90-95% (19, 20)), cytomegalovirus (CMV, seroprevalence 40-100% (21–23)), herpes simplex virus type 1 and 2 (HSV1/2; seroprevalence HSV1: 80-90%; HSV2: 10-25% (24, 25)), human parvovirus B19 (seroprevalence 40-80% (26, 27)), and Toxoplasma gondii (seroprevalence 50-77% (28, 29)).