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Effect of heat treatment and enzymatic digestion on the B cell epitopes of cow's milk proteins

Authors


Correspondence:
Kenji Matsumoto, Department of Allergy and Immunology, National Research Institute for Child Health and Development, 2-10-1 Okura, Setagaya-ku, Tokyo 157-8535, Japan. E-mail: kmatsumoto@nch.go.jp

Summary

Background Processing milk leads to changes in clinical allergenicity. However, the mechanism by which heat treatment affects the allergenicity of milk proteins is not fully understood.

Objective We investigated the effect of heat treatment and enzymatic digestion on the allergenicity of B cell epitopes of milk proteins using a histamine release assay.

Methods Human basophils were passively sensitized using sera from 10 patients with allergies to cow's milk. All the patients experienced symptoms immediately after ingesting milk. The human basophils were obtained from umbilical cord blood mononuclear cells after culturing the mononuclear cells for 3–4 weeks in the presence of IL-3. After sensitization with 10% patient sera for 48 h, the cells were stimulated with untreated, heat-treated, or heat-treated and pepsin-and-trypsin-digested β-lactoglobulin or α-casein for 1 h. The histamine concentrations in the supernatants were then measured by radioimmunoassay.

Results Heat treatment alone did not alter the molecular weight of β-lactoglobulin or α-casein. Heat treatment of β-lactoglobulin significantly increased its susceptibility to enzymatic digestion in a time- and temperature-dependent manner and reduced its ability to induce histamine release from sensitized basophils. Similar findings were not observed for α-casein. The combination of heat treatment and enzymatic digestion reduced the abilities of both β-lactoglobulin and α-casein to induce histamine release from passively sensitized basophils.

Conclusions Heat treatment reduced the allergenicity of β-lactoglobulin by inducing conformational changes and by increasing its susceptibility to enzymatic digestion, both of which disrupted B cell epitopes, whereas heat treatment alone did not alter the allergenicity of α-casein.

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