NOVEL PROTEINS OF PLASMODIUM-FALCIPARUM IDENTIFIED BY DIFFERENTIAL IMMUNOSCREENING USING IMMUNE AND PATIENT SERA

A differential serological screen of a lambda gt11 cDNA expression lib rary of Plasmodium falciparum was performed in an attempt to identify novel and putative host-protective antigens of the parasite. The scree ning was done with two categories of sera: (i) acute-phase sera obtain ed from smear-positive acutely infected P. falciparum patients from va rious regions in India and (ii) immune sera taken from healthy, perman ent adult residents of P. falciparum-endemic rural districts of Orissa in eastern India. These adults had not suffered from any clinical mal arial symptoms for at least the previous 3 years at the time of serum collection. Sixty-five clones obtained by screening the lambda gt11 li brary with two immune serum samples were analyzed extensively with a t otal of 70 acutely infected patient serum samples. Eight of these clon es failed to react with any of the patient sera. Each of these eight c lones, when tested individually with 92 serum samples from the immune group, reacted with a minimum of 43% of the samples from this category of sera. Thus, these eight epitopes may encode host-protective elemen ts since they are not recognized by antibodies in the patient sera but react exclusively and extensively with the clinically immune set. Seq uence analysis of two of these clones reveals that they are novel Plas modium genes.