PRIMARY AND SECONDARY INFECTIONS WITH CRYPTOSPORIDIUM-PARVUM IN IMMUNOSUPPRESSED ADULT MICE

The present study was undertaken to determine if infection of immunoco mpetent adult C57BL/6N mice with Cryptosporidium parvum would render t hem more resistant to a challenge infection following immunosuppressio n with dexamethasone (DEX). Fecal oocyst shedding and parasite coloniz ation of the terminal ilea were greater in immunosuppressed mice than in nonimmunosuppressed mice. Secondary infections with C. parvum resul ted in decreased oocyst shedding and reduced parasite colonization com pared with primary infections. Flow cytometry revealed fewer splenic B cells but more splenic total T, CD4(+) T, CD8(+) T cells and macropha ges in immunosuppressed mice than in nonimmunosuppressed mice. The CD4 (+) to CD8(+) T cell ratios and blastogenic responses to lipopolysacch aride (LPS), but not to concanavalin A, were decreased in immunosuppre ssed mice compared with nonimmunosuppressed mice. Blastogenic response s to LPS and percentages of splenic total B cells and macrophages were increased in secondary infections compared to primary infections. Enh anced susceptibility to C. parvum infection in immunosuppressed mice r evealed DEX-mediated effects on both cell-mediated and humoral immunit y. Our results suggest that increased resistance in immunosuppressed m ice to secondary infections with C. parvum may involve increases in B cells and macrophages.