Bone marrow CD4⁺ T cells are activated in normal mice. (A) Expression of activation antigens in normal BALB/c CD4⁺ BM T cells through flow cytometry analysis. Gated populations are CD69⁺ (top), CD62L^hi (middle), and CD45RB^interm or CD45RB^hi (bottom) populations. Their respective mean ± SD are shown in each plot. (B) Intracellular cytokine accumulation by BALB/c mesenteric lymph nodes (left) and bone marrow (right) T cells without exogenous stimulus. Gates show IL-4⁺CD3⁺ or IFNγ⁺CD3⁺ population and the respective mean ± SD are indicated. (C) Distribution of IL-4 and IFNγ production among CD4⁺ (□) and CD8⁺ (▦) BM T cells. Data are representative of 10 to 15 mice individually analyzed.