CD4+ and CD8+ T Cells Kill Intracellular Mycobacterium tuberculosis by a Perforin and Fas/Fas Ligand-Independent Mechanism

Abstract

Cytotoxic effector phenotype and function of MHC-restricted Mycobacterium tuberculosis (MTB)-reactive CD4+ and CD8+ T lymphocytes were analyzed from healthy tuberculin skin test-positive persons. After stimulation in vitro with MTB, both CD4+ and CD8+ T cells up-regulated mRNA expression for granzyme A and B, granulysin, perforin, and CD95L (Fas ligand). mRNA levels for these molecules were greater for resting CD8+ than CD4+ T cells. After MTB stimulation, mRNA levels were similar for both T cell subsets. Increased perforin and granulysin protein expression was confirmed in both in CD4+ and CD8+ T cells by flow cytometry. Both T cell subsets lysed MTB-infected monocytes. Biochemical inhibition of the granule exocytosis pathway in CD4+ and CD8+ T cells decreased cytolytic function by >90% in both T cell subsets. Ab blockade of the CD95-CD95L interaction decreased cytolytic function for both T cell populations by 25%. CD4+ and CD8+ T cells inhibited growth of intracellular MTB in autologous monocytes by 74% and 84%, respectively. However, inhibition of perforin activity, the CD95-CD95L interaction, or both CTL mechanisms did not affect CD4+ and CD8+ T cell mediated restriction of MTB growth. Thus, perforin and CD95-CD95L were not involved in CD4+ and CD8+ T cell mediated restriction of MTB growth.