MFR, A PUTATIVE RECEPTOR MEDIATING THE FUSION OF MACROPHAGES

We had previously identified a macrophage surface protein whose expres sion is highly induced, transient, and specific, as it is restricted t o actively fusing macrophages in vitro and in vivo. This protein is re cognized by monoclonal antibodies that block macrophage fusion. We hav e now purified this protein and cloned its corresponding cDNA. This pr otein belongs to the superfamily of immunoglobulins and is similar to immune antigen receptors such as the T-cell receptor, B-cell receptor, and viral receptors such as CD4. We have therefore named this protein macrophage fusion receptor (MFR). We show that the extracellular doma in of MFR prevents fusion of macrophages in vitro and therefore propos e that MFR belongs to the fusion machinery of macrophages, MFR is iden tical to SHPS-1 and BIT and is a homologue of P84, SIRP alpha, and MyD -1, all of which have been recently cloned and implicated in cell sign aling and cell-cell interaction events.