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An inexpensive animal model is described, for investigation of the immunogenicity of substances such as food additives. Inbred mice were immunised with antigen emulsified in complete Freund's adjuvant, and specific cell-mediated immunity subsequently measured by a footpad swelling test. This method has been applied in an investigation of the immunogenicity of the exudate gums, gum arabic, gum karaya and gum tragacanth. These substances are capable of eliciting an immune response which is comparable to the specific immune responses elicited by a protein antigen, e.g. hens' egg ovalbumin. Purification of commercially available gum preparations led to a significant (P less than 0.005) reduction of the immune response under in vivo test conditions.

Antibodies directed at gum arabic have been induced in rabbits immunized with gum arabic in Freund's complete adjuvant. These antibodies have been isolated in pure form by affinity chromatography on AH-Sepharose 4B containing gum arabic ligands. Oxidation of the susceptable carbohydrate residues of gum arabic with periodate or reduction of the glucuronic acid moieties with carbodiimide and borohydride converted the polysaccharide to products which no longer yielded precipitin reactions with the antibodies. The antibodies are therefore anti-carbohydrate antibodies with specificity for certain carbohydrate units of the gum arabic. Results of chemical modification and inhibition experiments indicate that 4-alpha-L-arabinofuranosyl-D-glucuronic acid units of the polysaccharide are the major immunodeterminant groups.

It is known that rabbit anti-gum arabic (GA) serum has cross-reactivity with Lea antigen, and that, by using this cross-reactive anti-Lea antibody, the presence of Lea antigen in red blood cells and saliva can be demonstrated with accuracy. We have devised a rapid and highly sensitive method for detecting Lea substance in human saliva by the enzyme-linked immunosorbent assay (ELISA) method using an anti-Lea antibody isolated from anti-GA serum by affinity chromatography on Synsorb Lea. The ELISA plate, coated with the specific anti-Lea antibody, adsorbed the Lea substance in saliva which was subsequently identified by adding enzyme labeled anti-Lea IgG in that order. The method could detect the Lea substance in Le(a+) saliva stains as small as 0.1 by 0.1 cm in size that had been stored at room temperature for three weeks and in Le(a+) saliva stains 0.7 by 0.7 cm in size that had been stored for ten years. This method seems to be useful for quantitative analyses of the Lea substance in various body fluids.

An animal model has been used to investigate the immunogenicity and non-specific irritant properties of exudate gums. The materials studied were four preparations of gum arabic (Acacia spp.), two of gum karaya (Sterculia spp.), two of gum tragacanth (Astralagus spp.) and a residue obtained after ethanol extraction of gum arabic. Groups of animals were intradermally immunized with the gum in complete Freund's adjuvant. Serum antibody levels were measured by an ELISA technique and delayed hypersensitivity responses by a footpad swelling test. Antigenic cross-reactivity within each gum species was tested in a crossover fashion. All gum preparations elicited systemic immune responses after immunization. Further processing reduced immunogenicity, although there was no evidence that systemic immunity to these complex polysaccharide antigens responses could be completely abolished by processing or purification. The ethanolic extract, and some of the gum preparations, particularly tragacanth and karaya, caused considerable footpad swelling when injected intradermally. It is concluded that processing and awareness of subspecies differences can reduce the inherent immunogenicity and potential irritant effects of exudate gums.