[Properties of an antigen-specific suppressor factor of immune spleen cells].

Splenocytes of mice immunized with sheep red blood cells (SRBC) were destroyed by ultrasound and ultracentrifuged at 20.000g for 30 min. The supernatant (SN) was used as a source for suppressor factors. It was shown that suppression in the given system was antigen-specific since the immune response of normal splenocytes (NS) transplanted along with SN into cyclophosphamide-treated (200 mg/kg) recipients considerably diminished in the course of immunization with SRBC rather than with rat red blood cells (RRBC). Absorption of SN with SRBC rather than with RRBC, mouse or human red blood cells completely abolished its suppressor activity. The suppressor factor was absorbed both by syngeneic and allogeneic splenocytes rather than by hepatocytes. The suppressor activity of SN considerably decreased after exposure to pronase and on heating at 56 degrees C for 1 h. The activity of immune serum against SRBC remained unchanged both on heating at 56 degrees C and after absorption with splenocytes. It is assumed that antigen-specific suppressor factor is a protein of non-immunoglobulin nature, bearing receptors for antigen and syngeneic or allogeneic splenocytes. A possibility of specific suppression of the immune response is discussed, not requiring restriction according to H-2 complex.