Identification of human acrosomal antigen SP-10 in primates and pigs

The intra-acrosomal human sperm protein SP-10 was previously designated a "primary vaccine candidate" by a World Health Organization Taskforce on Contraceptive Vaccines. In the present study, a monoclonal antibody to SP-10 (MHS-10) was employed on Western blots to identify immunoreactive SP-10 in sperm extracts from baboon (Papio cyanocephalus anubis) and two macaques (Macaca mulatta and Macaca fascicularis). In each of these primates, the MHS-10 monoclonal antibody recognized a polymorphic pattern of immunoreactive peptides similar to that in humans. Immunoreactive SP-10 was also demonstrated in pig sperm. Using purified preparations of the previously described intra-acrosomal molecules acrosin and sperminogen in the pig, we observed that the MHS-10 monoclonal antibody did not react with these proteins, indicating SP-10 is distinct from these known acrosomal components. Sperm from several common species including the rabbit, bull, rat, guinea pig and cat did not immunoreact with the MHS-10 monoclonal antibody. By use of a radioactive probe spanning 628 nucleotides of the open reading frame for SP-10 on Northern blots of poly A + RNA obtained from testes of Macaca fascicularis, Papio papio, and Papio cyanocephalus anubis, a 1.35-kb mRNA of identical size to the mRNA from human testes was identified. These results indicate that baboons, macaques, and pigs may be appropriate models for testing an SP-10-based contraceptive vaccine.