MOLECULAR-CLONING AND EXPRESSION OF CDNA-ENCODING HUMAN MACROPHAGE C-TYPE LECTIN

A human macrophage calcium-dependent (C-type) lectin cDNA clone was ob tained from a library derived from IL-2-treated peripheral blood monoc ytes. The cDNA cloning was based on the structural homology to hepatic asialoglycoprotein receptors. The nucleotide sequence of this cDNA cl one was homologous to those of the galactose- and N-acetylgalactosamin e-specific C-type macrophage lectins of rodents. In the putative carbo hydrate recognition domain, deduced amino acid sequence revealed 60 an d 63% homology to galactose- and N-acetylgalactosamine-specific C-type macrophage lectins of mice and rats, respectively. The cDNA clone was ligated into a mammalian expression vector and transfected into COS-1 cells. In the lysates of these cells, an M(r) 38,000 component, which bound to galactose-Sepharose, was identified after electrophoretic se paration by its interaction with polyclonal antisera against synthetic polypeptides representing a portion of the carbohydrate recognition d omain. The carbohydrate-binding specificity of the recombinant macroph age lectin was investigated by comparing elution profiles of various g lycopeptides having defined carbohydrate structures from immobilized m acrophage lectins. When N-terminal octapeptides from human glycophorin A that bore NeuAc alpha 2-3Gal beta 1-3 (NeuAc alpha 2-6) GalNAc and its sequentially deglycosylated derivatives were compared, glycopeptid es carrying three constitutive GalNAc-Ser/Thr (Tn Ag) strongly bound t o the recombinant human macrophage lectin. This is the first study to demonstrate that human macrophage cell surface lectin recognizes Tn Ag , a well-known human carcinoma-associated epitope.