CD8 T cells are in close proximity of IPCs in tonsil and provide a source of IL-3. (A-B) Colocalization of CD8 T cells and IPCs in the T-cell areas of tonsil. Cryosections from tonsils were stained with anti-BDCA-2 and anti-CD8, followed by Alexa 488-conjugated and Texas Red-conjugated secondary reagents. BDCA-2 is shown in green, CD8 in red, and DAPI nuclear stain in blue. Some of the HEVs are marked by white profiles. GC indicates germinal center. (For panel A, objective was 20 × /0.50 NA; for panel B, objective was 40 × /0.75 NA). (C) CD8 T cells were magnetically enriched from peripheral blood and sorted into CD45RA-/2B4^- central memory cells (left column), CD45RA^-/2B4⁺ effector-memory cells (middle column), CD45RA⁺/2B4⁺ effector cells (right column), and CD45RA⁺/2B4^- naive cells (not shown). Cytokine production of the sorted cell subsets was assessed by intracellular staining with anti-IL-2, IL-3, IFN-γ, and TNF-α following 6 hours of stimulation with PMA and ionomycin. Percentages of cytokine-secreting cells are indicated in each quadrant. Inserts in top panel represents fluorescence-activated cell sorting (FACS) profiles of individual CD8 T-cell subsets after intracellular staining with an antiperforin antibody.