Identification of novel protective antigens from Anaplasma marginale.

A successful recombinant vaccine against Anaplasma marginale remains elusive, despite intensive study of the protective, though variable major surface antigens. As an alternative approach to the discovery of additional antigens, crude parasite material was subjected to conventional protein fractionation, coupled with vaccination and parasite challenge trials, without making assumptions as to the nature or location of these antigens. This has lead to the identification of four novel antigens that, in microgram amounts, have significant protective effects in vaccination trials. The antigens have molecular weights in the range 17-43 kDa and isoelectric points above 7.8. Limited N-terminal and internal sequencing of these antigens has established that they are parasite proteins previously unreported in the literature, although one of the four is identifiable with a recently reported open reading frame of unknown function.