Cells involved in the immune response. XXXV. The antigen-specific antibody response in the rabbit is suppressed by thymocytes of allogeneic immunized rabbits (ITSC) and by the non-toxic suppressor factor (ITSF) secreted by these thymocytes.

ABSTRACT

The antigen-specific suppressor cells (ITSC) detected in the thymus of the rabbit 7 days post-iv immunization with sheep or horse erythrocytes (SRBC and HRBC, respectively), and the antigen-specific suppressor factor (ITSF) which the ITSC secrete in culture, inhibit the antigen-specific primary immune response in vivo when injected iv into SRBC and/or HRBC immunized rabbits on Days 0, 3, and 5 (ITSC) or daily on Days 0 to 5 (ITSF) post-primary immunization. The rabbits recover the ability to synthesize the specific antibodies following reimmunization by day 80 post-primary immunization. The primary immune response toward a non-cross-reacting antigen is not inhibited by the antigen-specific ITSC or ITSF. Neither the thymocytes of unimmunized rabbits nor the secretions of these cells in culture can suppress the primary immune response in vivo to either SRBC or HRBC. It must be emphasized that the suppression of the immune response by ITSC and ITSF in the rabbit is antigen-specific. ITSC and ITSF are not cytotoxic to rabbit lymphocytes in vitro. No gross or microscopic changes were detected in any of the lymphoid and nonlymphoid organs of rabbits sacrificed 2 days following 5 daily iv injections of large doses (10 ml) of ITSF. ITSF causes no adverse reaction in vivo since it did not induce morbidity in the rabbits during the 80 days observation period following its injection iv daily for 5 days commencing with the primary immunization.