Immunopathology of experimental Brucella abortus strain 19 infection of the genitalia of bulls

Antibody responses in serum and semen, and immunoglobulin containing cell (ICC) populations in the genitalia of bulls were compared after inoculating Brucella abortus strain 19 into the seminal vesicles of two bulls (ISV route) and into testes in two other bulls (IT route). Bulls seroconverted as early as 1 week post-infection (PI). Peak serum titres as determined by the serum agglutination test (SAT), complement fixation test (CFT) and ELISA occurred at PI weeks 3, 4 and 5 respectively. Highest titres were in IT inoculated bulls. Seminal antibodies against B. arbotus S19 were demonstrated from 2 weeks PI by both the SAT and the Rose Bengal Test (RBT) and highest titres occurred at PI weeks 3 and 4. Examination of immunoglobulins (Ig) in semen, however, revealed no significant differences of Ig isotypes between infected and control animals at any examination time. When bulls were killed at 7 weeks PI, quantitation of ICC in genital sections stained by the peroxidase-anti-peroxidase method revealed an overwhelming predominance of IgG containing cells in inflamed organs. In all cases IgG1- and IgG2-containing cells were prevalent, and present in approximately equal numbers. IgA-containing cells were second in prevalence in inflamed tissues while IgM cells were always in low percentage. High prevalence of ICC in infected genitalia, associated with elevated specific seminal antibodies but not with increased seminal Ig indicates that most Ig remains localised in tissues and is not transferred into genital secretions.