DIFFERENTIAL-EFFECTS OF CYTOLYTIC T-CELL SUBSETS ON INTRACELLULAR INFECTION

In analyzing mechanisms of protection against intracellular infections , a series of human CD1-restricted T cell lines of two distinct phenot ypes were derived. Both CD4(-)-CD8(-) (double-negative)T cells and CD8 (+) T cells efficiently lysed macrophages infected with Mycobacterium tuberculosis. The cytotoxicity of CD4(-)CD8(-) T cells was mediated by Fas-FasL interaction and had no effect on the viability of the mycoba cteria. The CD8(+) T cells lysed infected macrophages by a Fas-indepen dent, granule-dependent mechanism that resulted in killing of bacteria . These data indicate that two phenotypically distinct subsets of huma n cytolytic T lymphocytes use different mechanisms to kill infected ce lls and contribute in different ways to host defense against intracell ular infection.