Mycobacterium tuberculosis-specific CD8⁺ T Cells Preferentially Recognize Heavily Infected Cells

Both CD4⁺ and CD8⁺ T cells are important for successful immunity to tuberculosis and have redundant effector functions, such as cytolysis and release of potent antimycobacterial cytokines such as interferon-γ and tumor necrosis factor-α. We hypothesized that CD8⁺ T cells play a unique role in host defense to Mycobacterium tuberculosis infection as well. Possibilities include preferential and/ or enhanced release of granular constituents and/or preferential recognition of heavily infected cells. Utilizing human, Mycobacterium tuberculosis-specific, CD4⁺ and CD8⁺ T cell clones, we demonstrate that, after recognition of antigen-presenting cells displaying peptide antigen, CD4 ⁺ T cells preferentially release interferon-γ, whereas CD8 ⁺ T cells preferentially lyse antigen-presenting cells. Furthermore, utilizing dendritic cells infected with Mycobacterium tuberculosis expressing green fluorescent protein, we show that CD8⁺ T cells preferentially recognize heavily infected cells that constitute the minority of infected cells. These data support the hypothesis that the central role of CD8⁺ T cells in the control of infection with Mycobacterium tuberculosis may be that of surveillance; in essence, recognition of cells in which the containment of Mycobacterium tuberculosis is no longer effective.