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Schistosoma mansoni‐specific rat T cell clones. II. Different effects of adult worm‐specific T cell clones in immunocompetent and nude infected rats

The in vivo functional activities of two highly proliferating helper rat T cell clones (E23 and G5) specific for the excretory‐secretory antigens of Schistosoma mansoni adult worms were investigated. When injected into infected immunocompetent rats, both clones increased the antibody response against the 30–40‐kDa schistosomulum surface antigens, but failed to induce an immune protection. In contrast, when the same clones were injected into infected nude rats, a high degree of protection was obtained. In this latter case the absence of detectable specific antibody response, whether of IgE or IgG isotype, suggested that parasites were destroyed by an antibody‐independent mechanism, i.e. macrophages activation by lymphokines. Indeed supernatants obtained from T cell clones specifically restimulated with schistosome antigens expressed a macrophage activated activity similar to interferon‐γ. Following incubation with these supernatants or with the active fractions, macrophages exhibited a significant schistosomulicidal activity and both clones were shown to transfer an antigen‐specific delayed‐type hypersensitivity reaction to normal rats. Taken together these results demonstrate that, depending on the immune status of the host, antigen‐specific T cell clones can function differently and consequently that one function associated with one type of lymphokine could be favored.