Variant proteins of Plasmodium vivax are not clonally expressed in natural infections.

Plasmodium vivax is the most widely distributed human malaria parasite and responsible for 70-80 million clinical cases each year and a large socio-economical burden. The sequence of a chromosome end from P. vivax revealed the existence of a multigene superfamily, termed vir (P. vivax variant antigens), that can be subdivided into different subfamilies based on sequence similarity analysis and which represents close to 10-20% of the coding sequences of the parasite. Here we show that there is a vast repertoire of vir genes abundantly expressed in isolates obtained from human patients, that different vir gene subfamilies are transcribed in mature asexual blood stages by individual parasites, that VIR proteins are not clonally expressed and that there is no significant difference in the recognition of VIR-tags by immune sera of first-infected patients compared with sera of multiple-infected patients. These data provide to our knowledge the first comprehensive study of vir genes and their encoding variant proteins in natural infections and thus constitute a baseline for future studies of this multigene superfamily. Moreover, whereas our data are consistent with a major role of vir genes in natural infections, they are inconsistent with a predominant role in the strict sense of antigenic variation.