Obtention of monoclonal antibodies against human IgG4 using two different immunization strategies: development of a biotin-based ELISA for IgG4 quantitation.

Several monoclonal antibodies (MAbs) against human IgG4 have been produced in two fusion experiments. In fusion I, Balb/c mice were conventionally immunized and most of the antibodies obtained recognized IgG class-specific epitope(s). Therefore, a second fusion experiment was performed using IgG4-immunized mice that had been made tolerant to epitopes shared by the four IgG subclasses, and most of the hybridomas derived from this second fusion secreted antibodies specific for IgG4. Five MAbs which were found to be specific for both IgG4 isoallotypes (4a and 4b) were selected from the two fusion experiments. These antibodies define at least two non-overlapping epitopes located on the Fab and Fc regions of IgG4 molecule, respectively. Two MAbs were used to develop a two-site ELISA for IgG4 quantitation, in which one MAb (anti-Fab) was immobilized in the solid phase and the other one (anti-Fc) was biotin-labeled. The assay had a detection limit below 1 ng/ml and a practical working range between 4 and 200 ng/ml. The use of these MAbs should improve our understanding of the role of IgG4 in different clinical conditions.