Contact hypersensitivity reactions in βc^−/− and WT mice. C57BL/6 and BALB/c mice were sensitized with oxazolone on the abdomen and foot pads on day zero. Five days later, mice were challenged on the right ear with 0.5% oxazolone in acetone–olive oil. The left ear was treated with the carrier (acetone–olive oil) alone. The ear thickness was measured with a micrometer at 24 hours after challenge. Results are presented as the increased thickness of the hapten-treated ear minus the nonspecific swelling (carrier-treated ear). Data represent mean values of 5 mice per group. Similar results were obtained in 3 independent experiments.