Reactivity to SmCT-SOD of sera from individuals naturally infected with S. mansoni. Pooled sera were from acutely infected (AC; n = 4), chronically infected (asymptomatic intestinal [INT], n = 23; severe hepatosplenic [HS], n = 13), or uninfected (putatively resistant EN, n = 13; endemic area, egg negative [NEG/A], n = 6) individuals exposed to S. mansoni infection, as well as noninfected (NI; n = 5) individuals not exposed to S. mansoni infection. Sera were diluted 1:800, and ELISAs were performed using 5 μg of recombinant antigen (A) or hSOD (B) per ml. SmCT-SOD-MBP and MBP were analyzed separately, and the background was subtracted (SmCT-SOD-MBP response − MBP response = SmCT-SOD response). Dashes in panel A indicate the mean absorbance (OD) in each group. The cutoff value (line in panel A) was calculated using the mean + 3 SD of noninfected NI sera. Mouse anti-hSOD antibody was included as a positive control (B). The results represent the individual reactivity to SmCT-SOD. For the anti-hSOD reactivity, human sera were pooled. Analysis of variance showed that P was 0.08.