Prolonged Th1-like response generated by a Plasmodium yoelii-specific T cell clone allows complete clearance of infection in reconstituted mice

In the present study, we report the ability of in vitro cultured CD4(+) T cells, generated following immunization with dead blood stage P. yoelii parasites, to mediate protection against homologous challenge infection in reconstituted nude mice. P. yoelii-specific T cell line cells produced IFN-gamma after in vitro stimulation with specific antigen, and were protective when adoptively transferred into athymic nude mice. Following transfer of P. yoelii-specific T cell fines into nude and SCID mice, elevated levels of nitric oxide (NO) were detected during the first week of infection at a time when parasitaemias were suppressed. However, in vivo blocking of NO production through administration of L-NMMA, an inhibitor of NO synthase, increased mortality, but did not alter the course of primary parasitaemia in P. yoelii-specific T cell line-reconstituted nude mice. In addition, a P. yoelii-specific CD4(+) T cell clone, which produced IFN-gamma in vitro, afforded sterile protection via mechanisms other than NO. By ELISA, antibodies were undetectable on all but one day (day 79) post T cell clone transfer and parasite challenge, where very low levels of antibodies were detected, with some evidence of recognition of malaria proteins by Western blot. Collectively, our data suggest that T cell effector functions, independent of NO production and in the absence of high levels of parasite-specific antibodies, can contribute to sterile immunity to P. yoelii.