Serum-derived immunosuppressive substances. III. Regulation of the immune response by human serum alpha-globulin fractions: the dose-response relationship.

Suppression of the plaque-forming cell response in mice following injection of substances fractionated from pooled normal serum alpha-globulin was investigated. The dose-response relationship for fractions obtained by ion-exchange chromatography show that a single preparation has both enhancing and suppressive activities which are revealed at different doses. Whether this observation reflects the sum of activities of a number of molecular species remains to be determined. The immune responses to both thymus-dependent (heterologous erythrocytes) and thymus-independent (DNP-ficoll) antigens are suppressed while the response to the thymus-independent antigen lipopolysaccharide is enhanced. Thus, the cellular locus for immunosuppression cannot be exclusively on the T cell, and the magnitude of the action of the two populations (T and B cells) remains unclear.