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 bl ood and at the site of active disease in cattle 20 weeks after experimental infection with Mycobacterium bovis. Lymphocyte proliferation, and the prod uction of interferon-gamma (IFN-gamma) and interleukin (IL)-2 were measured in response to tuberculin and a number of mycobacterial antigens, includin g ESAT-6, MPB64, MPB70, MPB83, hsp 16.1, hsp 65, hsp 70 and the 38 000 MW l ipoprotein antigen. The level of transforming growth factor-beta (TGF-beta) was measured following stimulation of cells with tuberculin. Our results s uggest little difference in the responses of peripheral blood and lymph nod e cells to most of the antigens used. However, tuberculin purified protein derivative (PPD) and ESAT-6 elicited stronger responses in the peripheral b lood compared with lymph node cells. Investigation of the responding T-cell subpopulations in the peripheral blood showed that both CD4(+) and, to a l esser extent, gamma delta T-cell receptor-positive (TCR+) T cells contribut ed to these responses. This is the first report to compare peripheral and l ocal immune responses in bovine tuberculosis. Unlike cases of human tubercu losis where immune activity at the site of disease and anergy in the periph eral blood have been reported, our results suggest that for bovine tubercul osis immune responses occurring in the peripheral blood reflect those at th e site of disease.