Identification of a vir-orthologous immune evasion gene family from primate malaria parasites.

The immune evasion gene family of malaria parasites encodes variant surface proteins that are expressed at the surface of infected erythrocytes and help the parasite in evading the host immune response by means of antigenic variation. The identification of Plasmodium vivax vir orthologous immune evasion gene family from primate malaria parasites would provide new insight into the evolution of virulence and pathogenesis. Three vir subfamilies viz. vir-B, vir-D and vir-G were successfully PCR amplified from primate malaria parasites, cloned and sequenced. DNA sequence analysis confirmed orthologues of vir-D subfamily in Plasmodium cynomolgi, Plasmodium simium, Plasmodium simiovale and Plasmodium fieldi. The identified vir-D orthologues are 1-9 distinct members of the immune evasion gene family which have 68-83% sequence identity with vir-D and 71.2-98.5% sequence identity within the members identified from primate malaria parasites. The absence of other vir subfamilies among primate malaria parasites reflects the limitations in the experimental approach. This study clearly identified the presence of vir-D like sequences in four species of Plasmodium infecting primates that would be useful in understanding the evolution of virulence in malaria parasites.