Bovine tuberculosis: Immune responses in the peripheral blood and at the site of active disease

This report describes a comparison of immune responses in the peripheral blood and at the site of active disease in cattle 20 weeks after experimental infection with Mycobacterium bovis. Lymphocyte proliferation, and the production of interferon-γ (IFN-γ) and interleukin (IL)-2 were measured in response to tuberculin and a number of mycobacterial antigens, including ESAT-6, MPB64, MPB70, MPB83, hsp 16.1, hsp65, hsp70 and the 38,000 MW lipoprotein antigen. The level of transforming growth factor-β (TGF-β) was measured following stimulation of cells with tuberculin. Our results suggest little difference in the responses of peripheral blood and lymph node cells to most of the antigens used. However, tuberculin purified protein derivative (PPD) and ESAT-6 elicited stronger responses in the peripheral blood compared with lymph node cells. Investigation of the responding T-cell subpopulations in the peripheral blood showed that both CD4⁺ and, to a lesser extent, γδ T-cell receptor-positive (TCR⁺) T cells contributed to these responses. This is the first report to compare peripheral and local immune responses in bovine tuberculosis. Unlike cases of human tuberculosis where immune activity at the site of disease and anergy in the peripheral blood have been reported, our results suggest that for bovine tuberculosis immune responses occurring in the peripheral blood reflect those at the site of disease.