Blocking the IL-13–signaling pathway inhibits SS CD4⁺ T-cell proliferation. (A) Freshly isolated CD4⁺ T cells from SS patients were cultured in vitro for 5 days and treated with 10, 50, 100, or 500 ng/mL of IL-13. Proliferation was determined by MTT assay and data are depicted as means ± SD compared with untreated cells. Statistics were gathered by ANOVA followed by post hoc Dunnett test. (B) CD4⁺ T cells from SS patients (upper panel) or NDs (lower panel) were treated for 15 minutes with IL-4 or IL-13 and pSTAT-6 was determined by intracellular staining as described in Material and methods. Shown is a representative example of 5 independent experiments giving similar results. (C) Immunohistochemical analysis of pSTAT-6 from NS (n = 3), AD skin (n = 3), and stage I (n = 4) and stage IV (n = 4) CTCL skin biopsies. Representative examples are shown (original magnification ×400). (D) The percentages of pSTAT-6⁺ cells after quantification of 20 HPF for each sample are shown. Error bars are mean ± SD. Statistics were gathered by ANOVA followed by post hoc Tukey test. (E) Effect of a soluble IL-13Rα2 (2.5 μg/mL), an anti-IL-13 antibody (6.5 μg/mL), an anti-IL-4 antibody (10 μg/mL), or a pSTAT-6 inhibitor (AS1517499, 100 nM) on SS CD4⁺ T-cell proliferation. The proliferation inhibition rate was detected by MTT assay after 5 days in culture; the data are shown as means ± SD; ***P < .001 compared with the untreated cells. Statistics were gathered by ANOVA followed by post hoc Tukey test.