SPECIFIC BOVINE BRUCELLOSIS DIAGNOSIS BASED ON IN-VITRO ANTIGEN-SPECIFIC GAMMA-INTERFERON PRODUCTION

In order to improve the specificity of the diagnosis of bovine brucell osis, we developed a test which can be regarded as an in vitro correla te of the delayed-type hypersensitivity test (DTH). A mixture of cytop lasmic proteins from Brucella melitensis B115 was used as a specific a ntigenic stimulus in bovine whole blood culture. Supernatants harveste d at 18 to 24 h after the in vitro antigenic stimulus were assayed for their gamma interferon (IFN-gamma) content by using a commercial sand wich enzyme-linked immunosorbent assay kit. The IFN-gamma assay was ev aluated with 10 heifers during the course (80 days) of an experimental infection and with 14 cows from an ongoing brucellosis outbreak Ah of these animals were slaughtered, and pertinent organs were subjected t o classical bacteriological analyses. In addition, we analyzed 23 fiel d cases in which false-positive serological reactions occurred. The IF N-gamma results were compared with those of the standard DTH and a bat tery of serological assays, and they were correlated with bacteriologi cal data. Both for the experimental infection and for the field brucel losis outbreak, the IFN-gamma assay detected infection in more animals than any combination of the serological tests, and it detected infect ion earlier than these tests. Finally, none of the samples from cows s howing false-positive serological reactions was classified as positive by the IFN-gamma assay, attesting to its specificity and to its usefu lness in interpreting ambiguous serological results. A rapid and conve nient alternative to the DTH, the IFN-gamma assay appears to be an ide al method that is complementary to the serological diagnosis protocols .