SOCS3-deficient T cells are hyperresponsive to gp130 cytokines. Purified LN T cells were stimulated with IL-6 (A) or IL-27 (C) for the indicated times, and STAT activation was measured by immunoblotting with antibodies specific for phosphorylated STAT (P-Stat) proteins, as indicated. Antibodies specific for total STAT were used as loading controls. Activation of STAT3 in response to IL-6 (B) and IL-27 (D) was assayed by intracellular flow cytometry in CD8⁺ T cells. The mean fluorescence intensity (MFI) of phospho-STAT3 staining is shown below. Each data point represents mean (± SD) of values from 3 mice of each genotype. ■ indicates wt cells; □, Socs3^ΔLck/ΔLck cells. Data are representative of 2 to 3 independent experiments. *P < .05; **P < .001.