Analysis of circumsporozoite protein-specific immune responses following recent infection with Plasmodium vivax.

CD8(+) and CD4(+) T cells are involved in immunity to the pre-erythrocytic stage of malaria. This study has been undertaken to define T cell epitopes on the Plasmodium vivax circumsporozoite protein (CSP) and to analyze the early induction of immune response following infection. We identified CD4(+) and CD8(+) T epitopes recognized by different strains of mice as well as by humans. The CD4(+) T cell response in mice was found to be similar in all strains, but variation between strains was evident. Five H-2(d)-restricted CD8(+) cytotoxic T lymphocyte (CTL) epitopes, but no H-2(k)-or H-2(b)-restricted epitopes, could be defined. Non-H-2 genes were also able to regulate the response. In recently infected Thai adults, poor immunoresponsiveness was demonstrated. CTL activity and proliferative responses of T cells from malaria-exposed donors were very low. In contrast, exposed individuals had specific antibodies against the immunodominant repeats of both common strains of the P. vivax CSP; however, titers decreased following treatment.