Radioautographic study of cellular mechanisms in delayed hypersensitivity. IV. Distribution of injected lymph node, spleen, thymus and bone marrow cells.

Mononuclear cells from various organs of sensitized donor rats were labelled in vitro with tritiated leucine and injected intravenously into sensitized, syngeneic recipients. The localization of injected cells was studied in radioautographs. Bone marrow cells were the most frequent of the labelled cells in skin reactions. Equal numbers of bone marrow cells were found in specific and non-specific delayed reactions and irritation reactions induced with turpentine. Lymph node cells were found in delayed but not in turpentine reactions. Spleen cells were less frequent than lymph node cells in delayed skin reactions; small numbers were found in the turpentine reactions. Lymph node and spleen cells did not show detectable antigenic specificity. Thymus cells were not found in the skin sites, even when they were allowed to circulate 2–3 days in the recipients before biopsies were taken. Irrespective of the source of the cells injected few or no labelled cells were found in the recipient thymuses. Lymph node and spleen cells migrated equally into lymph nodes and spleen, but were infrequent in bone marrow. Only bone marrow cells had a decided preference for their organ of origin.