HUMAN IGE BINDING-CAPACITY OF TRYPTIC PEPTIDES FROM BOVINE ALPHA-LACTALBUMIN

The specific IgE binding capacity of native bovine alpha-lactalbumin ( alpha-La), a globular whey protein, and tryptic peptides was investiga ted using 19 sera from patients with cow's milk protein allergy. The s pecific anti-bovine alpha-La IgE titers ranged from 0.6 to 125 IU/ml. Highly purified tryptic peptides from native and disulfide-bond-reduce d alpha-La were obtained by reverse phase chromatography. By ELISA tec hnique using immobilized native protein or peptides, 11 of the 19 sera reacted exclusively with intact protein while 8 of them also presente d a specific IgE response to different tryptic peptides. Polyclonal Ig E population specificity was not related to anti-bovine alpha-La IgE l evels. Sequence (17G-K58) and larger peptides sharing this sequence we re most strongly and frequently recognized. Competitive ELISA inhibiti on tests confirmed this IgE-specific response and gave also clear evid ence for IgE binding to smaller peptides corresponding to sequences (6 C-R10):S-S(115L-L123) and (109A-L123). IgE binding to native alpha-La and large peptides confirmed the importance of conformational epitope( s). However, in some sera reduced and S-alkylated peptide (59I-K94) ex hibited a similar or higher IgE binding capacity than the native corre sponding fragment, suggesting the existence of sequential epitope(s) e xposed through protein denaturation. Moreover, IgE binding sequences w ere also located within hydrophobic regions of alpha-La and/or within parts with high sequence homology to human alpha-La.