The effects of antigenic stimulation upon graft-vs-host (GVHR) activity were studied in mice lethally irradiated between the time of immunization and subsequent inoculation of allogeneic thymocytes. The GVHR (measured as DNA synthesis in lymphoid tissue) was depressed in preimmunized animals, more so in secondarily immunized mice than in those that responded primarily. The suppression after secondary immunization was as pronounced in femoral lymph nodes as it was in the spleen, although all inoculations of antigen were intraperitoneal.

The findings illustrate that nonreactivity may be conferred upon normal allogeneic thymus-derived (T)-cells introduced into a milieu of antigenic competition. The concept of a body-wide, radiation resistant negative feedback factor appearing after antigenic stimulation is supported.

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