Characterization of aLactococcus lactisStrain That Secretes a Major Epitope of Bovine Beta-Lactoglobulin and Evaluation of Its Immunogenicity in Mice

Abstract

Bovine β-lactoglobulin (Blg) is one of the major cow's milk allergens. Peptide 41-60 of Blg (Blg41-60) was described as a murine T-cell determinant and a murine, rat, and human immunoglobulin E (IgE) epitope. The aim of this study was the expression of Blg41-60 as a fusion protein in the food-grade bacteriumLactococcus lactisand the characterization of its immunogenicity in mice. We constructed a recombinant strain ofL. lactiscapable of inducible production and secretion of Blg41-60::Nuc, a fusion protein between Blg41-60 and the mature part of the staphylococcal nuclease (Nuc). The highest production yield of Blg41-60::Nuc (32.5 mg/liter) was reached 4 h after induction. At this time, up to 75% of Blg41-60::Nuc was secreted. When monoclonal antibodies specific for Blg41-60 were used, purified Blg41-60::Nuc and synthetic Blg41-60 exhibited very similar immunoreactivities. Subcutaneous coadministration of purified Blg41-60::Nuc and killed nonrecombinantL. lactisresulted in the induction of specific anti-Blg41-60 IgG2a and IgG1. The IgG1/IgG2a ratio and the lack of specific IgE suggest a Th1-type immune response, i.e., a nonallergic response. Similar administrations of the killed Blg41-60::Nuc-producingL. lactisstrain did not elicit a specific immune response, whereas a transitory mucosal IgA-specific immune response was induced in mice after oral administration of the live Blg41-60::Nuc-producingL. lactisstrain.