Contact sensitivity in mice measured with thymidine labeled lymphocytes.

An ear assay was used to detect delayed responses in mice. Animals were sensitized and subsequently injected with 3H thyminedeoxyryribose to label antigen sensitive cells. Each animal was given a control and a test ear challenge and the respective responses were assessed by scintillation counting of 3H in cells which had accumulated at the reaction site. Delayed responses were consistently observed in animals sensitized to dinitrochlorobenzene (DNCB) but not in animals sensitized to sheep red blood cells. Reactivity to DNCB was minimal in tolerant animals and animals sensitized to the control agent. Both peritoneal exudate and spleen cells of antigen-sensitized animals were found to contain more label than cells from non-sensitized animals.