Serum IL-5 (pg/mL) in wild-type (WT) and interleukin-5–deficient (IL-5^–/–) C57Black/6 mice detected at 1 and 8 weeks after percutaneous inoculation with cercariae (40/mL) S mansoni versus uninfected controls. The detectable limit of the ELISA assay is indicated by the horizontal dashed line (7 pg/mL). The bars represent average ± standard error (SE) of values from 7 mice.