PLASMODIUM-YOELII - PEPTIDE IMMUNIZATION INDUCES PROTECTIVE CD4(-CELLS AGAINST A PREVIOUSLY UNRECOGNIZED CRYPTIC EPITOPE OF THE CIRCUMSPOROZOITE PROTEIN() T)

In this study we characterized the CD4(+) T cell response directed aga inst two distinct epitopes located in the circumsporozoite (CS) protei n of Plasmodium yoelii. The immunization of mice with P. yoelii sporoz oites induced CD4(+) T cells which were mostly directed against one of these peptides, Py-1, previously reported to contain a CD4(+) epitope . The CD4(+) T cells directed against this immunodominant epitope were mostly of the Th-1 type. Another newly identified peptide, AS44, indu ced a specific CD4(+) T cell response, which was mainly detectable aft er immunization with the corresponding peptide. Several CD4(+) T cell clones, recognizing this epitope, were generated and their lymphokine expression was characterized, as well as their surface markers and the ir anti-parasite activity in vivo. It was noteworthy that some of thes e CD4(+) T cell clones, which recognize this cryptic epitope and were of different Th subtypes, were shown to have a strong inhibitory effec t on the development of liver stages of malaria parasites. (C) 1996 Ac ademic Press, Inc.