FEMALE REPRODUCTIVE-TRACT IMMUNITY IN BOVINE TRICHOMONIASIS

PROBLEM: Mechanisms of protective immunity in the female reproductive tract are poorly understood. For sexually transmitted diseases, bovine trichomoniasis is a useful model because it resembles human trichomon iasis to some extent, and antibodies play an important role in protect ion against these extracellular parasites. Protective efficacy was com pared in animals with genital responses of predominantly immunoglobuli n G (IgG) or predominantly IgA antibodies to a purified surface antige n of Tritrichomonas foetus. METHOD OF STUDY: Immunization of mice by v arious routes with immunoaffinity-purified T. foetus surface antigen ( TF1.17) or killed cells was used to define the best routes and antigen combinations to give predominantly IgG or IgA antibodies to TF1.17 an tigens in genital secretions. Cattle were then immunized either subcut aneously (SC) two times with TF1.17 antigen and once SC with killed T. foetus or twice SC with TF1.17 antigen and once intravaginally with k illed T, foetus. All immunizations were in Quil A adjuvant. Controls w ere not immunized. Animals were challenged intravaginally with 10(6) T . foetus 3 weeks after the third immunization. Vaginal mucus was colle cted weekly for culture and antibody assays. Serum was collected weekl y, and uterine secretions were collected at 10 weeks post challenge. T issues were fixed at 10 weeks also. RESULTS: Murine studies showed sys temic priming with vaginal boosting gave the highest genital IEA respo nses. In cattle, systemic immunization (group S) induced high IgG1 ant ibody levels in vaginal secretions. Systemic priming with vaginal boos ting (group S/V) primed for an anamnestic vaginal IgA response after c hallenge with T. foetus. Cattle with predominantly IgG or predominantl y IgA responses in vaginal secretions either did not become infected o r cleared infection faster than controls. Uterine IgA responses at 10 weeks were highest in the vaginally boosted group, but other responses were no: different from the controls at this time point. Microscopic examination of genital tissues showed subepithelial infiltration of mo nonuclear cells in all groups. Lymphoid aggregates or nodules were det ected in vaginal sections in cattle of groups S/V and C as well as in uterine sections of all animals in all three groups. CONCLUSIONS: Both IgG and IgA antibodies to T. foetus superficial antigen were associat ed with protection. The timing of the response was related to the time of clearance. Lymphoid organization in the vagina and uterine tissues suggested development of mucosal inductive sites.