IN-VITRO IMMUNODIAGNOSTIC ASSAYS FOR BOVINE TUBERCULOSIS

The immune response to mycobacterial infections in cattle is predomina ntly cellular in nature and current diagnostic tests for M. bovis are based on the measurement of T cell responses. The low sensitivity of s erological assays for tuberculosis is therefore not surprising and ser ological tests will at best be used to complement rather than replace cellular assays. The recently developed bovine interferon gamma (IFN-g amma) assay is a rapid (24 hour) and simple whole blood in vitro assay , which in Australian field trials was found to be significantly more sensitive than the intradermal tuberculin test for the diagnosis of bo vine tuberculosis. The problem of false-positive reactions, due to the crossreactive nature of the antigen preparations used, can largely be overcome by using a comparative assay in which an animal's IFN-gamma response to bovine PPD and avian PPD are compared. Although reasonably M. bovis specific proteins have been identified and characterised, th eir use in either serological or cellular diagnostic assays is likely to be restricted due to the genetic diversity of the bovine immune res ponse to M. bovis infection.