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. Blg chemical hydrolysates appeared to retain most of the immunoreactivity of the native protein. Allergenicity of Blg has already been shown to be associated with the four peptides derived from cyanogen bromide cleavage of Blg.

Objectives: To map the major allergenic epitopes (e.g. regions of the molecule able to bind IgE) on Blg using specific IgE from sera of 46 milk-allergic patients as a probe.

Methods: Direct and competitive inhibition enzyme immunoassays involving immobilized native protein or purified peptides derived from Blg tryptic cleavage.

Results: Several peptides capable of specifically binding human IgEs were identified and were classified according to the intensity and frequency of the 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 recognized 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 scattered all along the Blg sequence.