Mab. 198: a monoclonal antibody recognizing the complement type 3 receptor (CR3) in the rabbit

A mouse monoclonal (Mab.198, IgG1) was generated that recognizes an epitope expressed on rabbit peripheral phagocytes and tissue macrophages. The membrane antigen recognized by Mab.198 consisted of two polypeptide chains of 165,000 and 95,000 molecular weight (MW). This Mab efficiently inhibited complement receptor-mediated granulocyte functions such as phagocytosis of complement-opsonized particulate antigens and zymosan-induced chemiluminescent responses. Fc receptor-mediated phagocyte functions were, on the contrary, barely affected by Mab.198. The cellular distribution, molecular structure and functional characteristics of the membrane antigen defined by Mab.198 suggested that this antibody recognizes the complement type 3 receptor (CR3). We found that Mab.M1/70, specific for mouse CR3 (i.e. CD 11 or Mac-1 antigen), also binds on rabbit phagocytes. However, this Mab recognizes a different CR3 epitope than Mab.198 as shown by cross-blocking experiments. This anti-rabbit CR3 Mab will be useful in the characterization of rabbit complement receptors and their involvement in immune reactions.