Analysis of the major epitope of the α2 chain of bovine type I collagen in children with bovine gelatin allergy

Background: Anaphylaxis to measles, mumps, and rubella vaccines has been reported. It has been found that most of these reactions to live vaccines are caused by type I allergy with the bovine gelatin present in the vaccines as an allergen. Gelatin mainly includes denatured type I collagen, which consists of α1 and α2 chains. We previously reported that allergic reactions to gelatin are caused by the type I collagen α2 (α2[I]) chain. Objective: To aid in the development of gelatin that has little or no allergenicity in human subjects, we investigated epitopes of bovine α2(I) chain with use of IgE in gelatin-sensitive children. Methods: Serum samples were collected from 15 patients who had systemic allergic reactions to vaccines and high levels of specific IgE to bovine gelatin. Eleven overlapping recombinant proteins that cover bovine α2(I) were prepared with a bacterial expression vector. We examined IgE reactivity to these recombinant proteins by means of ELISA. Fifteen peptides covering a major reactive recombinant protein were synthesized. The IgE-reacting epitope was identified by means of IgE-ELISA inhibition with these synthetic peptides and pooled serum from the patients. Results: We found that of the 15 patients, 13 showed IgE reactivity to a recombinant protein (no. 3) spanning the central region of the collagenous domain (418Gly-662Pro). Furthermore, all 13 patients showed IgE reactivity to the 4-kd recombinant protein (no. 3a) spanning the region from 461Pro to 500Glu. In IgE-ELISA inhibition we found that a minimum IgE epitope of gelatin allergen was composed of the 10-amino-acid sequence 485Ile-Pro-Gly-Glu-Phe-Gly-Leu-Pro-Gly-Pro494. This sequence is not observed in the human type I collagen α1 and α2 chains, nor is it found in the bovine type I collagen α1 chain. Conclusions: We found that Ile-Pro-Gly-Glu-Phe-Gly-Leu-Pro-Gly-Pro is a major IgE epitope of the α2 chain of bovine type I collagen in patients with gelatin allergy. The degree of anaphylaxis to gelatin in vaccines might be reduced by digestion of this IgE-binding site in gelatin. (J Allergy Clin Immunol 2002;110:652-7.)