Humoral response to FhCatB, FhCatL, and proregion of FhCatB following fluke infection in rats and sheep. Pools of rat (n = 4) (A) and sheep (n = 8) (B) sera collected from 0 to 10 weeks postinfection were tested for reactivity to cathepsin L, proFhCatB, and the proregion of CatB by ELISA, using plates coated with antigens at 4 μg/ml. The titers were plotted against time in weeks postinfection. Note that antibody titers to different antigens are illustrated using different scales.