CD6 crosslinking enhances T-cell proliferation and activation of NFAT. (A) PBLs (10⁵) were stimulated for 5 days with immobilized anti-CD3 (0.2 μg/mL), anti-CD28 (4 μg/mL), anti-CD6 (5 μg/mL), or combinations thereof. At day 5 proliferation was assessed by [³H]-thymidine incorporation. Mean values ± SEM of 3 independent experiments are shown. (B) Jurkat T cells were transfected with 5 μg of the NFAT-luciferase construct and stimulated for 6 hours with 1 μg/mL immobilized anti-CD3, anti-CD28 (4 μg/mL), anti-CD6 (1 μg/mL or 5 μg/mL), or combinations thereof. Luciferase activities were determined in cell lysates and expressed as percentages of the PMA (10 ng/mL)/ionomycin (1 μM) control. Nontransfected Jurkat cells did not respond to any stimulus (data not shown). Mean values ± SEM of 3 independent experiments are shown. Asterisks indicate significantly higher than anti-CD3 alone (Student t test, *P < .05; **P < .01).