I. Differences in Frequency of Splenic Precursor Cell~ Specific for a Synthetic Polypeptide Derived from Multichain Polyproline

Genetic controls of immune responses to natural and synthetic antigens are expressed by quantitative, autosomal traits (1). A number of separate dominant genes have been identified which regulate the ability of inbred strains of mice and guinea pigs to elicit specific immune responsesto these imlnunogens (2-13). Although two genetic loci have been shown to be linked to histocompatibility regions of the mouse genome (12, 14, 15), little is known concerning the genetic mechanisms responsible for the control of immunity. In view of the number of complex cellular events required for immune processes, it is likely that at least certain genetic controls will be demonstrable at the cellular level. In fact, responses of mice to synthetic polypeptides based on mulfichain polyalanine and responses of guinea pigs to poly-L-lysine have been achieved by the injection of responder lymphoid cells into irradiated nonresponder animals (1, 14). Such transfer experiments suggest that these genetic defects reside in potentially immunocompetent cells, although the nature of the cellular deficiency is not fully understood. Previous results indicate that the so-called "nonresponder" mice do produce small amounts of antibody to poly-L-(Tyr, Glu)-poly-L-Pro--poly-L-Lys, denoted (T, G)-Pro--L (10, 11). I t is possible, therefore, that the genetic defect in the low responder DBA/1 strain could be attributed to a reduced number of immunocompetent precursor cells responsive to (T, G)-Pro--L when compared with the number in the high-responder SJL strain.