The nature of the impurity in BGG that inhibits induction of tolerance in Balb/C mice will be studied in an effort to determine its physicochemical nature, its interaction with macrophages and the mechanism by which it averts tolerance to the major component. The reaction of various classes of human IgG with macrophages from Balb/C and DBA/2 mice will be correlated with their abilities to induce tolerance in these two strains. The conditions for achieving ABA hapten specific suppression in guinea pigs and rats will be further detailed and the nature of the cell causing the suppression examined by column separation and reaction with antiserum to various cell markers. An ABA helper, DNP plaque forming system will be set up to examine the target for ABA suppressor cells, whether they operate at the helper T cell or B cell level. BIBLIOGRAPHIC REFERENCES: Paley, R.S., Leskowitz, S., and Borel, Y. Effect on tolerance induction of the mode of attachment of the hapten to the carrier. J. Immunol. 115: 1409, 1975. Stadecker, M., and Leskowitz, S. The inhibition of cutaneous basophil hypersensitivity reactions by a heterologous anti-guinea pig T cell serum. J. Immunol. 116: 1646, 1976.