Mouse Macrophage Hemagglutinin (sheep Erythrocyte Receptor) with Specificity for Sialylated Glycoconjugates Characterized by a Monoclonal Antibody

The functions of resident macrophages (MO)' in hematopoietic and lymphoid organs are poorly understood . In several species, in situ immunocytochemical staining with MO-specific mAbs has demonstrated that these tissues contain large numbers of stromal MO, even in the absence of overt inflammation or immune stimulation (1-6). We and others have previously speculated that stromal MO may perform diverse local homeostatic functions, including regulation of growth, differentiation and movement of hematopoietic and lymphoid cells (7, 8) . Our experimental approach has been to isolate the relevant MO populations anddetermine whether they possess novel features that could be involved in cellular interactions . We have focused on murine bone marrow, since this tissue contains an arborizing network of stromal MO that establish intimate adhesive contacts with proliferating erythroid andmyeloid cells (1, 7) . After their isolation, the majority ofresident bone marrow MO express a novel receptor, sheep erythrocyte receptor (SER), which mediates the binding, but not ingestion, of unopsonized sheep erythrocytes (E) (9). Since it is possible that SER normally interacts with a homologous ligand on mouse bone marrow cells it was of interest to characterize its properties and distribution. SER is a divalent cation-independent, lectin-like hemagglutinin that recognizes sialylated glycoconjugates on the erythrocyte surface . Its properties are similar to the "ganglioside receptor" on rat MO described by Riedl and colleagues (10) . In addition to resident bone marrow MO, the receptor is expressed at high levels on isolated stromal lymph node MO but it is low or undetectable on monocytes or peritoneal, pleural, and bronchoalveolar MO. These features indicate that SER may be involved in interactions of stromal MO with ligands on neighboring cells or extracellular matrix components .