Anti-PGL-I levels before and at diagnosis of leprosy were compared in more detail: six out of 12 (50.0%) incident MB cases tested seropositive for anti-PGL-I IgM at some point during the study (S3 Fig); three incident cases who initially tested seronegative, were seropositive for anti-PGL-I IgM at the time of diagnosis. The gene discussed is CD40LG; the disease is leprosy.