Observations on acacia as an immunizing, sensitizing, anaphylactogenic, and desensitizing antigen

Abstract

Four different lots of gum acacia were found to be equally effective as immunizing, sensitizing, anaphylactogenic, and desensitizing antigens, as shown by cross-precipitin tests and cross-anaphylaxis experiments. The antigenicity of acacia is considered to be a property of the native substance, and not due to a contaminant or impurity. Rabbits were readily immunized with, and guinea pigs actively sensitized to, acacia. Antiacacia rabbit serum in small doses passively sensitized guinea pigs. They reacted to intravenous and aerosol challenges with acacia. This sensitization lasted about thirteen days. Homologous antiacacia serum also passively sensitized guinea pigs, but none of these pigs has reacted, so far, to an aerosol challenge with acacia. The duration of passive sensitization with homologous serum was not studied. Precipitins persisted in rabbits for six to seven weeks after intravenous immunization, and for three months after a single subcutaneous injection of acacia with Freund's adjuvant. Precipitin behavior was bizarre in that precipitates could not be collected by centrifugation, although specific ring tests were obtained with ease. Passively sensitized guinea pigs were effectively desensitized by intraabdominal injections of acacia. Exposure to acacia acrosol produced dyspnea in a high percentage of actively, passively, and congenitally sensitized animals. Continued or repeated aerosol exposure produced local desensitization readily in passively sensitized guinea pigs. Desensitization of actively sensitized pigs took much longer. Arthus type reactions to intracutaneous injections of acacia in immunized rabbits were obtained in varying degree. Desensitization against this type of reaction followed intravenous injections of several large doses of acacia. Formamide-treated acacia had a lower nitrogen content than the native gum, but was still antigenic, although its anaphylactogenic and precipitating powers seemed to be reduced. Formamide-treated acacia precipitated globulin (chiefly gamma, by crude tests) from normal and immune guinea pig and rabbit serum. Heating the acacia did not appreciably affect its specificity or immunizing properties. Treatment of acacia by several methods, using acid or alkali with and without heat, failed to yield a haptenic polysaccharide, although nonhaptenic polysaccharides which had lost their immunologic specificity were obtained readily.