Detection of Mycobacterium bovis infection in cattle using an immunoassay for bovine soluble interleukin-2 receptor-α (sIL-2R-α) 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-α (IL-2R-α) followed by the release of a soluble form of the molecule (sIL-2R-α) from the membrane of the stimulated cells. The present study investigates the novel use of the release of sIL-2R-α 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-α produced following incubation of bovine peripheral blood mononuclear cells with mycobacterial antigens. Using this assay, 6367 cattle naturally infected with M. bovis were identified whereas only 151 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.