FIG. 3.

Flow cytometric detection of intracellular IFN-γ in Apa-stimulated (A) and M. tuberculosis sonicate-stimulated (B) T cells. Whole blood was stimulated with recombinant Apa protein of M. tuberculosis or M. tuberculosis sonicate for 6 h, fixed, and stained for CD3 (fluorescein isothiocyanate), CD8 (phycoerythrin), and IFN-γ (Cychrome). Cells were gated sequentially on lymphocytes, followed by CD3, and analyzed for expression of CD8 and IFN-γ. The frequencies in the upper quadrants are IFN-γ-producing cells as percentages of the total CD4⁺ (left quadrants) or CD8⁺ (right quadrants) T cells.