On the function of repetitive domains in protein antigens of Plasmodium and other eukaryotic parasites.

Highly reiterated repetitive domains occur within the protein antigens of many parasitic taxa, including Plasmodium, Trypanosoma, Leishmania and Toxoplasma. In malaria it has been proposed that repeat regions may function as ligands for host proteins, or serve to suppress the development of immunity through a strategy of serological crossreactivity. In this article Louis Schofield presents a novel hypothesis, based on empirical evidence, that repetitive domains in antigens do not elicit protective immune responses and instead have evolved as a mechanism of immune evasion by their ability to induce thymus-independent B-cell activation. It is also proposed that this unusual response is associated with several forms of immunosuppression. The hypothesis has the added attraction of helping to explain several distinctive features of the molecular biology, evolution and immunology of repetitive regions in protein antigens of parasites.