[Suppressive factor release by mouse lymphocytes after incubation with syngeneic erythrocytes]

Suppressive factor, inhibiting the immune response to sheep red blood cells, is released after incubation in vitro of spleen cells of (CBA X C57BL) F1 mice, immunized with rat erythrocytes, in contact with syngeneic erythrocytes. Intravenous immunization results in the factor release by thymus and/or spleen cells but not by the bone marrow or lymph node cells. It is suggested that the factor is not antigen-specific and is secreted by non-specific T cells suppressors after the contact with syngeneic erythrocytes.