CBA and C57 mice were tested for their ability to make an immune response to a related series of branched, multichain synthetic polypeptide antigens in which the antigenic determinants on the amino termini of the branched side chains were systematically varied. Neither strain responded to the polyglutamic acid determinant. Both strains responded well and equally to the poly(phenylalanine, glutamic acid) determinants. CBA mice responded poorly, and C57 mice responded well to two different antigens bearing poly(tyrosine, glutamic acid) determinants. CBA mice responded well, and CS7 mice responded poorly to two different antigens bearing poly(histidine, glutamic acid) determinants.

The genetic control of the immune response to (H,G)-A--L appears to be dominant and polygenic, as it has been shown to be for (T,G)-A--L.

The related antigens used in this study show extensive cross-reactions with antisera against other members of the related series.