A critical role for IL-12 in CCR5 induction on T cell receptor-triggered mouse CD4⁺ and CD8⁺ T cells

Despite increasing evidence for the role of the chemokine system in leukocyte trafficking, the mechanism underlying the induction of chemokine receptors is poorly understood. Here, we investigated how CCR5, a chemokine receptor implicated in T cell migration to inflammatory sites, is induced in the T cell. CCR5 mRNA was hardly detected in resting T cells and marginally induced following T cell receptor (TCR) stimulation. However, TCR-triggered T cells expressed IL-12 receptor, and stimulation with recombinant IL-12 resulted in high levels of CCR5 expression on both CD4⁺ and CD8⁺ T cells. In contrast, IL-2 failed to up-regulate CCR5 expression. The effect of IL-12 was selective to CCR5 because IL-12 did not up-regulate CXCR3 expression. Surface expression of CCR5 was shown by staining with anti-CCR5 monoclonal antibody. Stimulation of these CCR5-positive T cells with the relevant chemokine MIP-1α elicited Ca²⁺ influx, showing that IL-12-induced CCR5 is functional. These results indicate a critical role for IL-12 in the induction of CCR5 on TCR-triggered T cells.