UVB-INDUCED IMMUNE SUPPRESSION AND INFECTION WITH SCHISTOSOMA-MANSONI

Irradiation with ultraviolet B (UVB, 290-320 nm) causes a systemic imm unosuppression of cell-mediated immunity. The question of whether UV i mmunosuppression modulates the course of infectious diseases is import ant because UVB levels in sunlight are sufficient to predict significa nt UV-induced immunosuppression at most latitudes. We have investigate d the effect of immunosuppressive doses of UVB on the disease caused b y the helminth parasite Schistosoma mansoni. C57BL/6 mice were irradia ted once or three times weekly over 60-80 days with UV from a bank of FS40 sunlamps. Each UV treatment consisted of an immunosuppressive UV dose, as determined by suppression of contact hypersensitivity to trin itrochlorobenzene, corresponding to about 15-30 min of noonday tropica l sunlight exposure under ideal clear sky conditions. Cumulative UV do ses were between 80 and 170 kJ/m(2). Worm and egg burdens, liver granu loma diameters and liver fibrosis showed minimal changes (<20%) compar ed with parameters in unirradiated animals. Ultraviolet irradiation (a total of 55 kJ/m(2) administered in six treatments) did not impair th e resistance to rechallenge conferred by vaccination with Co-60-irradi ated cercariae. We have thus observed a dichotomy between UV immunosup pression and both disease and vaccination in this helminth infection, in contrast to the effects of UVB shown in other infectious diseases.