Résumé
Glycosyl-phosphatidylinositol anchor merozoite surface antigens (GPI-anchor MSA) are proposed to act in the invasion process of infective merozoites of
Babesia into host erythrocytes. Because of their essential function in the survival of
Babesia parasites, they constitute good candidates for the development of vaccines against babesiosis and they have been extensively analyzed. These include
Babesia bovis variable MSA (VMSA) and
Babesia bigemina gp45/gp55 proteins of the agents of bovine babesiosis from tropical and subtropical countries, and the
Babesia divergens Bd37 and
Babesia canis Bc28 proteins of the main agents of bovine and canine babesiosis in Europe, respectively. However, these are very polymorphic antigens and
Babesia parasites have evolved molecular mechanisms that enable these antigens to evade the host immune system as a survival strategy. This review focuses on the genetic basis of GPI-anchor MSA polymorphism and the antigenic diversity of B-cell epitopes that might be generated in each of these
Babesia species. The picture is incomplete and no
Babesia genome sequence is yet available. However, the available sequences suggest that two distinct, non cross-reactive GPI-anchor MSA (i.e., with unique B-cell epitopes) may be required by all
Babesia species for invasion, and that these two distinct GPI-anchor MSA would be encoded by a multigene family. Furthermore, the data are consistent with the ability of biological clones from
Babesia to use these multigene families for the expression of GPI-anchor MSA, either conserved (
B. canis and
B. bovis) or polymorphic (
B. divergens and
B. bigemina) in their amino acid sequence. Moreover, as a consequence for successful parasitism, the data suggest that both conserved and polymorphic GPI-anchor MSA would present unique B-cell epitopes.