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The ability of mice to form antibodies against the random terpolymer glu57lys38ala5 is controlled by a codominant Mendelian factor. Three of 7 inbred strains were 100 per cent responders; the others were completely negative. All of these strains could make antibody to related polymers with higher alanine content (10 and 40 mole per cent). Breeding studies using the progeny of Swiss mice indicated that a similar genetic factor was involved.

The RNA extracted from normal peritoneal macrophages exposed to a linear, random synthetic polypeptide, Glu(60)Ala(30)Tyr(10), initiated an immune response in C57B1/6J mice, although this strain responds very poorly to the antigen itself. From 10 to 150 micrograms of RNA obtained from mouse, rat, or rabbit macrophages was injected intraperitoneally into recipient mice, and specific antibody was detectable by passive hemagglutination 3 to 4 weeks later. Treatment of the RNA with ribonuclease destroyed its ability to initiate a specific immune response. The RNA contained by weight 0.02 percent of the (specific) antigen. The RNA obtained from cells incubated with a second polypeptide, Glu(36)Lys(24)Ala(40), initiated a response specific for this polymer. This RNA even when incubated in vitro with Glu(60)Ala(30)Tyr(10) failed to initiate antibody formation specific for Glu(60)Ala(30)Tyr(10).

The antigenicity of synthetic polymers of a-amino acids has been studied in various species for different reasons. The original impetus to these investigations was the search for highly polymerized protein-like materials that could possibly be used as plasma volume expanders. Interest in these materials has increased since their anfigenicity offers a means of determining the minimum structural requirements for anfigenicity in protein-like materials. By the application of quantitative immunochemical studies with small polypeptides it may be possible to determine the size and structure of the antigenic unit and the nature of combining sites in the antibody.Previous reports have dealt with the antigenicity in humans of synthetic poly-a-glutamic acid (1) and random copolymers of glutamic acid and lysine (2). The present report will deal with the study in humans of additional copolymers consisting of 3 and 4 amino acids. The anfigenicity of the 4 polymers used in this study has been established previously in rabbits (3) and guinea pigs (4). Materials and MethodsThe copolymers studied for antigenicity in humans are listed in Table I. The methods used in preparing the materials and the techniques employed in determining the average molecular weights are presented in references 5-10. After withdrawal of 50 ml of blood the human volunteers were skln-tested with 0.1 ml of polymer solutions of 10 mg/ml and 1 mg/ml and 0.1 ml of the 0.15 ~ saline buffer. The individuals then received 5 intramuscular injections of the appropriate polymer solutions given over a period of 10 days. With antigens GLA5 and GLT a total of 125 mg was injected into 6 and 5 individuals respectively. With antigens GLA40 and GLAT, 6 individuals in each group received a total of 12.5 mg and other groups of 6 received 125 mg. The bleedings and skin testings were repeated about 12 and 21 days after the last injection.

The response of mice to synthetic linear polypeptides of known composition but random sequence has been studied. Neither Swiss mice nor a number of inbred strains could respond to copolymers of only 2 amino acids (G60L40, G60A40, G90T10). Upon introduction of as little as 4 mole per cent of a third amino acid, good immune responses were obtained, regardless of the nature of the third amino acid. The level of the immune response to a series of glu-lys-ala polymers increased with increasing alanine content of the polymer.

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Previous reports from this laboratory have dealt with observations on the immunogenicity in rabbits (1-5), guinea pigs (6, 7), and man (8) of synthetic random copolymers consisting of 2 and 3 L-a-amino acids. In the rabbit studies, the copolymers consisting of the amino acids, glutamic acid and alanine, in a ratio of 60:40 (G60A40) t and the terpolymer consisting of the latter amino acids and lysine (G~L~sAs0) were very effective antigens and have repeatedly been so in our laboratory. This latter terpolymer has also been found to be highly antigenic in guinea pigs (7), man (8), and mice (9). The experiments presented in this report on the immunogenicity of a new group of polymers were undertaken to learn: (a) whether polymers consisting of other ratios of glutamic acid and alanine or glutamic acid and other amino acids are effective antigens; (b) the possible basis for the enhanced immunogenicity of G4~asA,0. When negative or poor responses were noted with the polymers in rabbits, the material was then tested in guinea pigs. This report will present the findings on the immunogenicity of the preparations and a subsequent publication will present the quantitative relationships among the various polymers and their antisera. Materials and MethodsMaterials.- Table I lists the random polymers studied. The methods employed in preparing the polymers from the N-carboxy a-amino acid anhydrides, their characterization and the techniques *

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