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A Nonspecific Immunosuppressive Material Derived from Normal Bovine Serum 1

Summary An improved method of purification of a potent, nonspecific immunosuppressant from normal serum is described. The suppressive agent was shown to be heat stable and filterable through a membrane with exclusion above 10,000 mol wt. The active molecule appears to bind to larger molecules from which it is released by heating. Preliminary data suggest that the active principle is a peptide with a mol wt of approximately 8000. Immunosuppression was reversed by administration of antigen-antibody complexes, rather than antigen alone. Antibodies of the IgM class were more effective than IgG antibodies in reversing immunosuppression. Experiments on reversal of immunosuppression suggest that the suppressive agent may interfere with antigen recognition, which is postulated to be a function of the concentration of preformed, circulating, specific antibodies.