CONSERVATION OF A PROTECTIVE SURFACE-ANTIGEN OF TRITRICHOMONAS-FETUS

Bovine trichomoniasis is a sexually transmitted disease caused by the flagellated protozoan Tritrichomonas foetus. A protective surface anti gen was previously identified and immunoaffinity purified from T. foet us isolate D1 with cross-reactive monoclonal antibodies (MAbs) TF1.15 and TF1.17 (BonDurant, R. H., R. R. Corbeil, and L. B. Corbeil, Infect . Immun. 61:1385-1394, 1993). This antigen elicited antibody responses in the serum and cervicovaginal mucus of heifers. Thus, it may be use ful as an immunodiagnostic reagent as well as a subunit vaccine. Conse rvation of the antigen in all strains would be crucial for either appl ication. We investigated the conservation of this antigen among 36 iso lates of T. foetus from Argentina, Costa Rica, and the United States u sing MAbs TF1.15 and TF1.17 in an enzyme-linked immunosorbent assay. M Ab TF1.17 reacted with 32 of the 36 isolates, whereas MAb TF1.15 react ed with all of the isolates tested. One of the isolates which did not react with MAb TF1.17 (i.e., D1#3) was investigated further by Western blotting (immunoblotting) to determine the reason for the lack of rea ctivity with one of the two cross-reactive MAbs. The antigenic band th at was reactive with MAb TF1.15 had a molecular mass slightly lower th an that of the corresponding band from isolate D1, which reacted with both MAbs TF1.15 and TF1.17. Thus, at least a major portion of the ant igen appeared to be conserved. This was confirmed in a study of heifer s infected with isolate D1#3. The vaginal immunoglobulin A antibodies of these infected heifers reacted with the antigen of isolate Dl that was immunoaffinity purified with MAb TF1.17. Therefore, even though th e epitope recognized by MAb TF1.17 was missing in the challenge isolat e (D1#3), the heifers developed an immune response to the rest of the molecule. These results indicate that the major portion of the previou sly described protective antigen is conserved in different isolates of T. foetus. This portion contains the epitope that reacts with MAb TF1 .15. Most isolates express the whole antigen, which possesses both TF1 .15 and TF1.17 epitopes, but the few isolates that are missing the por tion containing the TF1.17 epitope may still elicit an immune response to the conserved portion. Thus, the protective surface antigen is pro mising for use in immunodiagnosis or vaccination against bovine tricho moniasis.