Abstract
Aggregation of the high-affinity receptor for immunoglobulin E, FcεRI, on mast cells and basophils leads to the release of mediators responsible for allergic symptoms in the presence of receptor-bound IgE and multivalent allergens. Reagents to inhibit the IgE-binding to FcεRI have been vigorously investigated in the last two decades. The mouse anti-human FcεRIα monoclonal antibody CRA 2, that we established previously, efficiently inhibits human IgE-binding to the human FcεRI. Therefore, its Fab fragments have therapeutic potential in the treatment of allergy. Here we described the humanization of CRA 2 by CDR-grafting onto human variable region frameworks. The humanized CRA 2 had almost the same activities of binding to the FcεRI and inhibition for IgE-binding to the FcεRI as the original mouse CRA 2. Furthermore, pretreatment of human peripheral blood basophils with the Fab fragments of the humanized CRA 2 as well as those of the mouse CRA 2 prevented the subsequent degranulation of human basophils activated by crosslinking of the FcεRI with IgE and anti-IgE antibody. In the humanized CRA 2, all amino acid residues except CDR were replaced with the residues encoded by human germline genes. The successful humanization of CRA 2 may be an important step in the development of immunotherapy to manipulate the IgE network.
