A mouse monoclonal IgE antibody anti bovine milk b-lactoglobulin allows studies of allergy in the gastrointestinal tract (1)
Four- to six-week old female Balb/c mice were injected weekly subcutaneously (s.c.) and intraperitoneally (i.p.) with 0.5 ml of a 2.5% alum suspension containing 20 ug of b-LG. In anti b-LG antibodies positive 20 hybrid supernatants, only one elicited a PCA reaction which was positive upto titre of 1/2,000 and was totally abolished by heat treatment (2h at 56C). The purification procedure was efficient as shown by SDS polyacrylamide gel electrophoresis in reducing and non-reducing conditions.
Amino acid analysis and carbohydrate content were determined.
Incubation with the same amount of IgE molecules on both b-LG preparations resulted in a much stronger binding to heat-treated b-LG coated wells. The binding of the IgE to native or aggregated b-LG was similar. After challenge with 0 1 ml of fresh milk, containing approximately 3 mg/ml b-LG, no PCA reaction could be detected. To rule out the possibility of a milk factor interfering with mast cell degranulation, b-LG was purified from fresh milk and injected in the same conditions. Again, no PCA reaction was seen. However, challenge with polymerized b-LG gave a PCA reaction similar to that observed with heat-treated b-LG.
Carbon leakage was evident upon visual examination of the gastrointestinal tract. The leak was most pronounced in the jejunum and of decreasing intensity along the small intestine. The large intestine was unaffected. Histological examination of the affected region showed oedema within the villae, but without detectable modification of the epithelial cells.
The binding to both native and aggregated b-LG seems to exclude the production of a neo-antigenic determinant by heat treatment. However, the absence of PCA with native (or non-aggregated b-LG) is intriguing because b-LG is a dimeric molecule which should fulfil the requirements for mast cell degranulation. The monoclonal antibody recognizes one conformational determinant per dimeric b-LG molecule. The dissociation of native b-LG at 37C into two monomers might also play a role.