Lymphokines in sensitized rats (II). Skin reacting factors and lymphnode activating substances originating from thymocytes.

In vivo activity upon draining popliteal lymphnodes of lymphokine-containing thymic cell culture supernatants from rats sensitized to PPD was studied after subcutaneous injection into footpads of normal recipients. Also inflammatory skin responses after intradermal injection of the same supernatants into the same untreated animals were studied. It appeared that only concentrated culture supernatants from antigen-stimulated thymic cell cultures were able to cause paracortical changes in draining lymphnodes after subcutaneous injection, and inflammatory skin reactions after intradermal injection in untreated animals in contrast to control supernatants. The results confirm the hypothesis that a population of cells must be present in the thymus of the sensitized rat which is able to produce lymphokines after contact with specific antigen.