SIALOADHESIN BINDS PREFERENTIALLY TO CELLS OF THE GRANULOCYTIC LINEAGE

Sialoadhesin is a macrophage-restricted, sialic acid-dependent recepto r of 185 kD that binds to the oligosaccharide sequence NeuAc alpha 2,3 Gal on cell surface glycoconjugates. Recent cDNA cloning has shown tha t sialoadhesin is a new member of the immunoglobulin superfamily with sequence similarity to CD22, a sialic acid-dependent receptor of B lym phocytes. Sialoadhesin has been implicated in cellular interactions of stromal macrophages with developing myeloid cells. In this study, dir ect evidence for this interaction was obtained in cell-cell binding as says using both native and recombinant forms of the protein. In all as says, sialoadhesin exhibited specific, differential binding to various murine cell populations of hemopoietic origin. In rank order, siaload hesin bound neutrophils > bone marrow cells = blood leukocytes > lymph ocytes > thymocytes. Single-cell analyses confirmed that sialoadhesin selectively bound myeloid cells in complex cell mixtures obtained from the bone marrow and blood. In comparison, a recombinant Fc-chimeric f orm of murine CD22 showed high binding to B and T lymphocytes, but ver y low binding to immature and mature myeloid cells. These results are consistent with the notion that sialoadhesin is involved in interactio ns with granulocytes at different stages of their life histories.