Expression of cell surface lectins on activated human lymphoid cells

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Abstract
A cell surface lectin found on activated human lymphoid cells has been identified and characterized using membrane glycoprotein micelles as probes. These micelles, which are large, water‐soluble aggregates, are composed of glycoproteins isolated from detergent‐solubilized membranes of human B lymphoblastoid cell lines by Lens culinaris hemagglutinin affinity chromatography. The micelles have an average apparent molecular weight of 4 × 106 estimated by gel filtration and range in diameter from 25‐100 nm. Micelles bind to B and T lymphoblastoid cell line cells and peripheral blood lymphocytes activated with concanavalin A or in a mixed lymphocyte response. Unactivated peripheral blood lymphocytes and red blood cells bind very low levels of the micelles. The binding is saturable, reversible, and temperature‐dependent, with poor binding below 15 °C. Glycoproteins such as fetuin and porcine thyroglobulin, which contain complex oligosaccharide side chains, inhibit the binding, whereas glycoproteins containing only high mannose or simple serine‐linked carbohydrate side chains do not. In addition, binding can be inhibited by complex asparagine‐linked glycopeptides purified from pronase‐digested fetuin, but not by the simple serine‐linked glycopeptides. Membrane glycoprotein micelles are bound to the surface of the cells but are not internalized or degraded. The potential role of this cell surface lectin in lymphocyte function is discussed.