CXCR3 neutralization leads to partial loss of PMP-mediated inhibition of IL-17 production by Tregs. Tregs were isolated from healthy donors and cultured for 7 days with anti-CD3/anti-CD28 mAb–coated beads and recombinant human IL-2, IL-15, and IL-1β in the presence or absence of 1.5 × 10⁶ allogeneic PMPs isolated from platelet apheresis units of 3 healthy donors. Flow cytometry analyses of intracellular cytokines were performed after stimulation with PMA and ionomycin, in the presence of Brefeldin A. (A) Example dot plots of day 7 CXCR3 expression on Tregs. (B) CXCR3 expression on Tregs throughout culture. (C) CXCR3⁺ Tregs present in the CD41⁻ and CD41⁺ subpopulations in time. (D) Day 7 intracellular staining of IL-17 on Tregs cultured with or without PMPs in the absence or presence of isotype or antagonistic anti-CXCR3 mAb. The percent PMP-mediated inhibition of IL-17–expressing Tregs is displayed in the graph. Results for 3 Treg donors are shown. Mean and SD are shown. *P < .05.