Antigens in penicillin allergy. II. The influence of the number of penicilloyl residues on the antigenicity of macromolecules as determined by radioimmunoassay (RIA), passive cutaneous anaphylaxis (PCA) and antibody induction.

The present communication reveals a relationship between the epitope density of penicilloylated protein antigens and their antigenic activities in a radioimmunoassay (RIA), in passive cutaneous anaphylaxis (PCA) and in inducing antibody formation in mice. In the RIA and PCA a critical number of 2-4 penicilloyl residues per protein molecule was noted. At this level small changes in the number of substituents considerably influenced the antigenic activities. The molecular weight and the nature of the carrier proteins, myoglobin, bovine serum albumin (BSA) and dimeric BSA also affected the threshold concentration for efficient antigenic activity. The results with the RIA and PCA were significantly correlated to each other. Using penicilloylated BSA as immunizing antigen in mice it was found that an epitope number higher than 11 penicilloyl residues per protein molecule induced significant antibody formation after a single injection. Antigens with a lower degree of penicilloyl substitution were less immunogenic. An antigen carrying 0.6 penicilloyl residues per BSA molecule did not induce penicilloyl-specific antibodies even after three injections. The capacity of heavily penicilloylated proteins to induce and elicit penicillin allergy as revealed by the present results stresses the importance of limiting their presence in penicillin preparations.