Distinct T cell specificities are induced with the authentic versus recombinant Plasmodium berghei circumsporozoite protein.

Plasmodium berghei sporozoite (SPZ)-immune lymph node (LN) cells obtained from mice of different H-2 haplotypes were analyzed for the presence of circumsporozoite (CS) protein-reactive T cells in proliferative assays. Although lymphocytes from each strain responded in vitro to the priming Ag and to the soluble rCS protein, they did not respond to CS protein synthetic peptides. Parallel analysis of rCS protein-primed LN cells revealed that the two Ag are unequal in generating T cell specificities: although SPZ priming did not induce CS protein peptide-reactive T cells, priming with rCS protein did. Not being privy to the processing and presentation of SPZ Ag, we postulated that a different order of processing of the authentic, i.e., SPZ-associated CS protein vs soluble rCS protein might be responsible for the generation of different T cell specificities. Accordingly, authentic CS protein might not be processed by APC, or the processed fragments might obscure the recognition of smaller peptide fragments. Therefore, we subjected the SPZ to three cycles of a freeze/thaw procedure and used the denatured SPZ preparation for priming. We observed that contrary to priming with the authentic SPZ, denatured SPZ generated T cells reactive to some of the CS protein synthetic peptides. The hypothesis that each form of the SPZ Ag is subject to a unique Ag processing was also confirmed in experiments demonstrating a lack of recognition of the authentic CS protein by rCS protein-primed LN cells. Hence, the evidence presented in this work that complex protozoan Ag, such as Plasmodia, might present different requirements for Ag-specific T cell induction/activation not only enhances the basic understanding of the immune system, but is essential for the development of antimalaria vaccine(s). In addition, these observations support the hypothesis that the molecular context of the priming Ag influences the outcome of T cell specificities, by providing evidence that the authentic CS protein induces a T cell repertoire that is distinct from that induced by the rCS protein.