Effects of in vivo T lymphocyte subset depletion on mycobacterial infections in mice

The relative importance of CD4⁺ and CD8⁺ T cell subsets in the expression of acquired resistance to systemic infection by Mycobacterium kansasii was determined. T cell subsets were depleted in thymectomized C57BL/6 mice by the intravenous administration of monoclonal antibodies directed against the relevant T cell determinants. Depletion of the CD4⁺ subset exacerbated the severity of the infection in intravenously challenged mice. This effect was apparent in the first 2 weeks of the infection and persisted throughout the 12 weeks of the study. On the other hand, depletion of the CD8⁺ cells had no apparent effect on the growth curves. Infections by Mycobacterium tuberculosis Erdman or bacille Calmette-Guerin (BCG) Pasteur were also substantially enhanced by CD4 depletion, but not by the depletion of CD8⁺ cells. The effect of subset depletion on infections by M. tuberculosis and BCG was examined in both innately susceptible C57BL/6 mice and innately resistant B6D2 mice.