Natural Suppressor Cell Systems

Abstract

Natural suppressor (NS) activity is a potent immunosuppressive mechanism. NS activity is usually measured by the inhibition of proliferation of normal cells, and not by lysis. NS activity can be seen in unprimed populations, such as in normal mouse bone marrow or newborn spleen, or after manipulations such as total lymphoid irradiation (TLI), induction of chronic graft-vs-host disease (GVHD), or cyclophosphamide administration. Cells with NS activity appear to be null cells and do not carry markers of mature T or B cells. They inhibit proliferation in a genetically unrestricted manner. They are nonadherent, and band in light density Percoll fractions, thus resembling large granular lymphocytes or leukocytes. NS activity is greatly increased by T cell signals including lectin-free Con A supernatants, IL-2, and IFN-γ. NS activity is prominent in tissues in which hematopoiesis is vigorous, and may play an important role in many situations including bone marrow transplantation and the use of cytotoxic drugs. It may also be relevant to problems of self-tolerance and autoimmunity.