Detection of Mycobacterium bovis infection in cattle using an immunoassay for bovine soluble interleukin-2 receptor-alpha (sIL-2R-alpha) produced by peripheral blood T-lymphocytes following incubation with tuberculin PPD.

After activation of T-lymphocytes with antigen there is an increase in the expression of interleukin-2 receptor-alpha (IL-2R-alpha) followed by the release of a soluble form of the molecule (sIL-2R-alpha) from the membrane of the stimulated cells. The present study investigates the novel use of the release of sIL-2R-alpha from activated T-lymphocytes as a marker of cell-mediated immunity (CMI) in cattle infected with Mycobacterium bovis. An enzyme immunoassay was used to detect sIL-2R-alpha produced following incubation of bovine peripheral blood mononuclear cells with mycobacterial antigens. Using this assay, 63/67 cattle naturally infected with M. bovis were identified whereas only 1/51 uninfected animals were considered to give a positive result. This assay is more convenient to use than lymphocyte proliferation assays which involve the use of radionucleosides. It should prove useful for monitoring the immunological activation of bovine T-lymphocytes in a variety of situations including the development of CMI responses in cattle to novel mycobacterial antigens or potential vaccines.