Partial protection of baboons against Schistosoma mansoni using radiation-attenuated cryopreserved schistosomula.

ABSTRACT

Three groups of five baboons were vaccinated in Kenya using three doses of 10,000 viable cryopreserved schistosomula attenuated with either 10, 20 or 60 krad 60Co-irradiation prepared in England. Animals were vaccinated at four-week intervals, challenged after a further six weeks with 2,000 cercariae and perfused at 10 weeks after challenge. High antibody titres to schistosomula mediating in vitro cytoadherence with P 388D1 macrophage-like cells were demonstrated in all vaccinated animals but not in controls. Significant titres to soluble egg antigen (SEA) were also demonstrated by ELISA in the 10 and 20 krad vaccinated groups following the first vaccination. The subsequent vaccinations and the challenge boosted this response considerably. Mean anti-SEA titres were only elevated above background in the 60-krad group six weeks after the third vaccination and in the challenge controls six weeks after challenge. Peripheral eosinophil counts were slightly reduced and neutrophil counts slightly elevated before challenge while eosinophil and erythrocyte counts were elevated and neutrophil counts depressed after challenge. PCV values were erratic in all groups. Eggs appeared in the faeces from six weeks after challenge and excretion rates were higher in all three vaccinated groups than in the challenge controls by necropsy 10 weeks after challenge. Body-weights were depressed in all groups after challenge but subsequently rose in the 10 and 20 krad groups. The 60 krad and challenge control groups lost 12.4% and 7.9% of body-weight respectively after challenge.(ABSTRACT TRUNCATED AT 250 WORDS)