Allergy to bovine beta-lactoglobulin: specificity of human IgE to tryptic peptides

Background Bovine beta-lactoglobulin (Blg) is a major cow's milk allergen. It is the main whey protein, without any counterpart in human milk. Big che mical hydrolysates appeared to retain most of the immunoreactivity of the n ative protein. Allergenicity of Big has already been shown to be associated with the four peptides derived from cyanogen bromide cleavage of Big. Objectives To map the major allergenic epitopes (e.g. regions of the molecu le able to bind IgE) on Big using specific IgE from sera of 46 milk-allergi c patients as a probe. Methods Direct and competitive inhibition enzyme immunoassays involving imm obilized native protein or purified peptides derived from Big tryptic cleav age. Results Several peptides capable of specifically binding human IgEs were id entified and were classified according to the intensity and frequency of th e responses. The major epitopes appeared to be fragments (41-60), (102-124) and (149-162) recognized by 92, 97 and 89% of sera, respectively, whilst a second group which contained the fragments (1-8) and (25-40) was recognize d by 58 and 72% of the population. A third group, comprising peptides (9-14 ), (84-91) and (92-100), was still detected by more than 40% of sera. Conclusion Three peptides were identified as major epitopes, recognized by a large majority of human IgE antibodies. Numerous other epitopes are scatt ered all along the Big sequence.