Abstract
Plasmodium vivax is a very common but non-cultivable malaria parasite affecting large human population in tropical world. To develop therapeutic reagents for this malaria, the parasite molecules involved in host-parasite interaction need to be investigated as they form effective vaccine or drug targets. We have investigated here the erythrocyte binding activity of a group of 15 different Plasmodium vivax tryptophan rich antigens (PvTRAgs). Only six of them, named PvTRAg, PvTRAg38, PvTRAg33.5, PvTRAg35.2 PvTRAg69.4 and PvATRAg74, showed binding to host erythrocytes. That the PvTRAgs binding to host erythrocytes was specific was evident from the competitive inhibition and saturation kinetics results. The erythrocyte receptors for these six PvTRAgs were resistant to trypsin and neuraminidase. These receptors were also chymotrypsin resistant except the receptors for PvTRAg38 and PvATRAg74 which were partially sensitive to this enzyme. The cross-competition studies showed that the chymotrypsin resistant RBC receptor for each of these two proteins was different. Altogether, there seems to be three RBC receptors for these six PvTRAgs and each PvTRAg has two RBC receptors. Both RBC receptors for PvTRAg, PvTRAg69.4, PvTRAg33.5, and PvTRAg35.2 were common to all these four proteins. These four PvTRAgs also shared one of their RBC receptors with PvTRAg38 as well as with PvATRAg74. The erythrocyte binding activity of these six PvTRAgs was inhibited by the respective rabbit polyclonal antibodies as well as by the natural antibodies produced by the P. vivax exposed individuals. It is concluded that only selective few PvTRAgs show erythrocyte binding activity involving different receptor molecules which can be blocked by the natural antibodies. Further studies on these receptor and ligands may lead to the development of therapeutic reagents for P. vivax malaria.
Highlights
Plasmodium vivax affects millions of people every year worldwide
Plasmodium vivax contains the largest number of tryptophan-rich antigens, called Plasmodium vivax tryptophan rich antigens (PvTRAgs), than any other human malaria parasite
Our data suggests that these PvTRAgs are interacting with the host erythrocytes and not to the lymphocytes (Fig. 1 inset)
Summary
Plasmodium vivax affects millions of people every year worldwide. This parasite remains non-cultivable in the laboratory. The disease caused by P. vivax was considered benign as compared to P. falciparum. Recent reports indicate that, like P. falciparum, this parasite can cause complications and increases severity of the disease [1,2,3,4]. There is emergence of drug resistance in P. vivax [5,6,7,8,9]. Efforts should be made for the development of new therapeutic approaches in order to control this parasitic disease
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