Early emergence of CD8(+) T cells primed for production of type 1 cytokines in the lungs of Mycobacterium tuberculosis-infected mice

Several lines of evidence suggest that CD8 T cells are important in protect ion against tuberculosis. To understand the function of this cell populatio n in the immune response against Mycobacterium tuberculosis, T cells from l ungs of M. tuberculosis-infected mice were examined by flow cytometry. The kinetics of the appearance of CD8 T cells in lungs of infected mice closely paralleled that of CD4 T cells. Both CD4(+) and CD8(+) T cells displaying an activated phenotype mere found in the lungs as early as 1 week postinfec tion. By 2 weeks, total cell numbers in the lungs had tripled and percentag es of T cells mere increased two- to threefold; the percentages of CD4(+) T cells were ca. twofold higher than those of CD8(+) T cells. Short-term sti mulation with M. tuberculosis-infected antigen-presenting cells induced cyt okine production by primed CD4(+) and CD8(+) T cells. Intracellular cytokin e staining revealed that 30% +/- 5% of CD4(+) and 23% +/- 4% of CD8(+) T ce lls were primed for production of gamma interferon (IFN-gamma). However, a difference in in vivo IFN-gamma production by T cells was observed with sim ilar to 12% of CD4(+) T cells and similar to 5% of CD8(+) T cells secreting cytokine in the lungs at any given time during infection, The data present ed indicate that although early in infection the majority of IFN-gamma is p roduced by CD4(+) T cells, cytokine-producing CD8(+) T cells are readily av ailable when triggered by the appropriate stimuli.