Minimal molecular size of dextran required to elicit heterologous passive cutaneous anaphylaxis in guinea pigs.

Abstract

1. Isomaltohexaose and smaller molecular fragments of dextran were found incapable of eliciting passive cutaneous anaphylaxis (PCA) in guinea pigs maximally sensitized with rabbit antidextrans. 2. Isomaltodecaose elicited PCA in maximally, but not in submaximally sensitized animals. This indicates that monovalency or bivalency is not always expression of a physical characteristic of an anaphylaxis elicitor, but may be considered a functional property, dependent on the density of cell-fixed antibody populations. 3. The PCA-eliciting effect of isomaltodecaose could be inhibited by admixture of isomaltohexaose. 4. The finding that, among the oligosaccharides tested, isomaltodecaose is the smallest molecular fragment of dextran capable of eliciting PCA, is in accord with literature data on the dimensions of the antidextran-binding site. 5. PCA titers of 60 samples of rabbit antidextran antisera, estimated in guinea pigs, showed a range from 500 to 1,800, with a precipitating antidextran content of 0.8–3.6 mg/ml in 9 of these sera. The smallest amount of antidextran, detectable by PCA, and producing lesions in 50% of sites injected, was found to be 0.02–0.09 <i>μ</i>g. An approximately linear relationship between diameter of PCA lesions and log dose of antidextran was obtained.