Fig 4

Activated T cells in the circulation detected by footpad Delayed-Type Hypersensitivity (DTH) assay. a Reactivity after vaccination with 500 RA cercariae. Two identical experiments are plotted showing the Th1 cells reach a peak at approximately 17 days and have declined almost to background levels before challenge at 35 days. b Reactivity of vaccinated mice (V + C) and naïve controls (CC) challenged at 5 weeks with 200 normal cercariae. A sharp increase in circulating T cells is observed 7 days after challenge of the vaccinated animals, coincident with peak schistosomula numbers in the lungs, and then a gradual decline. The reactivity of the control mice is muted in comparison, both with respect to the previously vaccinated animals and to the naïve mice in part A exposed to RA cercariae. The gradually rising DTH response of the CC group up to day 20 is most likely a response to worm vomitus released by the blood feeding worms accumulating in the liver. Replotted from [57]