Characterization of a differential immunoscreen epitope of Plasmodium falciparum using combinatorial agents

A differential serological screening of a lambda gt11 cDNA expression libra ry has identified several clones, which react exclusively to sera samples f rom persons clinically immune to malaria but not to acute malaria patient s era. One such clone, IPf9, has a 315-bp cDNA insert, which was found to be conserved in different strains of the human and rodent malarial parasite Pl asmodium falciparum and Plasmodium berghei, respectively. The induced expre ssion product of IPf9 was used to generate polyclonal sera in rabbits. The IPf9 expression product was also screened with phage surface display combin atorial libraries to isolate reagents that specifically bound to the IPf9 p roduct. The polyclonal antisera and the combinatorial reagents recognized a 50-kDa protein from P. falciparum, and a 53-kDa product from P. berghei. I mmunofluorescence studies using asexual and sexual stages of P. falciparum showed the protein to be present within the parasite in each of the asexual and sexual stages. The combinatorial reagents showed a partial inhibition in the growth of P. falciparum in vitro. Mice infected with the P. berghei showed the presence of T-cells that exhibited lymphoproliferation when stim ulated with the IPf9 protein. It is suggested that IPf9 protein is a conser ved protein epitope, and may be relevant for a protective immune response t o malaria.