Cellular and humoral immune responses to a recombinant P. falciparum CS protein in sporozoite-immunized rodents and human volunteers

Abstract

The immune responses of sporozoite-immunized rodents and of human volunteers exposed to multiple bites of irradiated Plasmodium falciparum infected mosquitos have been investigated using a yeast-derived recombinant P. falciparum circumsporozoite (rPfCS) protein. The murine immune response to immunization with rPfCS was not genetically restricted. Nine different murine haplotypes, when immunized with rPfCS, developed high levels of antisporozoite antibodies detectable by IFA and RIA. In addition, injection of rPfCS induced a secondary antibody response in P. falciparum sporozoite-primed mice. Murine T-cell epitopes were mapped in the C terminus of the rPfCS protein using overlapping synthetic peptides. The human T-cell response was investigated using T-cell clones derived from peripheral blood lymphocytes (PBL) of a P. falciparum sporozoite-immunized volunteer. A total of 40 CD4+ T-cell clones were obtained. Stimulation indices ranged from 2.5 to 103.4 following challenge with rPfCS in the presence, but not in the absence, of antigen-presenting cells. The clones were specific for rPfCs and did not proliferate or secrete lymphokines when challenged with yeast-derived recombinant P. vivax or P. berghei CS protein or with a yeast-extract control. The clones also recognized the native CS protein in extracts of P. falciparum, but not P. berghei or P. cynomolgi, sporozoites.