CD200 is required for UVB-mediated suppression of contact hypersensitivity. Wild-type (WT) or CD200-deficient (CD200^-/-) mice were either exposed (+ UVB) or not exposed to UVB prior to hapten sensitization and challenge. Ear thickness was measured at both 24 (not shown) and 48 hours. ^*Significantly different from all other groups (P < .01) by Student t test. Results shown are representative from 2 replicate experiments. Error bars indicate ±1 SD.