FIGURE 4.

CD26 costimulation enhances IL-26 production in HuCB CD4 T cells, and blockade by the CD26 ligand caveolin-1 reduces production of IL-26. (A) HuCB CD4 T cells were stimulated with immobilized anti-CD3 (0.05 μg ml⁻¹) plus anti-CD28 (10 μg ml⁻¹) or anti-CD26 (10 μg ml⁻¹) mAbs. After 7 d of stimulation, mRNA levels of human IL2, IFNG, IL17A, IL26, and DPP4 were quantified by real-time RT-PCR. Each expression was normalized to HPRT1. Data are shown as mean ± SEM, resulting from three independent experiments with triplicates. *p < 0.05, **^,***p < 0.0001. (B) HuCB CD4 T cells were stimulated with plate-bound anti-CD3, anti-CD28, anti-CD26 mAbs, or Cav-Ig immobilized at the indicated concentration. The supernatants were harvested 7 or 14 d after stimulation, and levels of human IL-26 were quantified. Data are shown as mean ± SEM, resulting from three independent experiments with triplicates (*^,**p < 0.0001 or ***p < 0.05 versus corresponding samples at day 0). (C) HuCB CD4 T cells were treated with blocking Cav-Ig (solid line) or control Ig (dotted line) at the indicated concentration. After 1 h of incubation with blocking Cav-Ig or control Ig, cells were stimulated with immobilized anti-CD3 (0.05 μg ml⁻¹) plus Cav-Ig (20 μg ml⁻¹), anti-CD28 (20 μg ml⁻¹), or anti-CD26 (20 μg ml⁻¹) mAbs. After 7 d of stimulation, the supernatants were harvested and levels of human IL-26 were quantified. Data are shown as mean ± SEM, resulting from three independent experiments with triplicates. *p < 0.0001 versus corresponding control Ig.