CD28-triggering enhances T-cell trafficking into nonlymphoid organs and promotes promiscuous T-cell recruitment to homing-“privileged” sites. Infiltration of the indicated tissues by HY-specific WT (A-G) and Y170F T cells (H-N) following CD28 ligation (PKH26 labeled) or treatment with a control antibody (CFSE labeled) is shown. Each panel shows a representative tissue image (scale bar: 30 μm). The mean T-cell infiltration ± SD observed in samples from at least 3 animals is shown (A, *P < .007; B, *P < .05; C, *P < .03; D, *P < .004; F *P < .003).