IL-17–producing T “memory” lymphocytes are present in mice that lack adaptive Th17 cells. (A–C) CD44^hiCD62L^low αβ T cells sorted from WT and IL-6/-21R DKO mice (A), WT and IL-6/-21R/-23R TKO (B), or DKO and TKO mice (C) and stimulated for 72 h with αCD3, IL-1β, and/or IL-23. Brefeldin A was added the last 6 h in culture. Cells were harvested, fixed, and permeabilized and stained for intracellular IL-17 and IFNγ. Flow dot plots represent cytokine production after stimulation between WT and TKO mice, and numbers represent frequencies of cytokine production. (C) Bars in graphs represent the mean frequency ± SEM of IL-17⁺ cells after culture. n = 3 (αCD3), 5 (αCD3+IL-1β), and 5 (αCD3+IL-1β+IL-23); each n consists of pooled cells from at least three mice.