Immune and non-immune responses to monovalent low molecular weight penicilloyl-polylysines and penicilloyl-bacitracin in rabbits and guinea-pigs.

Rabbits and guinea-pigs have been immunized with low molecular weight penicilloyl—polylysines (BPO1—PLL1 2, BPO6—PLL1 2) with varying degrees of substitution and with monovalent penicilloyl—bacitracin (BPO1—BAC). The immune response to the penicilloyl (BPO) determinant has been followed by skin tests, passive haemagglutination, passive cutaneous anaphylaxis (PCA), immunodiffusion and immunoelectrophoresis. Maximally substituted BPO6—PLL1 2 was found to be non-immunogenic. Apparently monovalent BPO1—PLL1 2, which inhibits precipitation of anti-BPO antibodies in vitro, was found to induce delayed-type hypersensitivity and antibodies for BPO in most of our random bred and in all strain 2 guinea-pigs. The delayed hypersensitivity in some of the sensitized guinea-pigs was hapten (BPO)-specific. BPO1—PLL1 2 was very poorly immunogenic in rabbits. Monovalent BPO1—BAC induced BPO-specific delayed hypersensitivity and anti-BPO antibodies in some random bred guinea-pigs but not in strain 2 animals. BPO1—BAC induced good levels of haemagglutinating anti-BPO antibodies in most random bred rabbits. Truly monovalent compounds, such as BPO1—BAC or BPO—ε-aminocaproate, do not elicit antibody-dependent reactions such as anaphylactic or Arthus reactions, but inhibit them. On the other hand, apparently monovalent BPO1—PLL1 2 was found to elicit BPO-specific PCA and Arthus reactions in immunized rabbits and guinea-pigs. When administered in higher doses, similar reactions were produced in non-immunized guinea-pigs. The possibility is discussed that some of the reactions observed with basic polypeptide antigens are due to the formation of mixed `specific antibody—polypeptide—non-specific protein' complexes formed in vivo by electrostatic interaction.