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We report the cloning of a novel human type I cell surface Ag mainly expressed by macrophages. The primary structure was established by molecular cloning, which yielded a 4579-bp cDNA sequence encoding a polypeptide chain of 1453 amino acid residues with 16 potential N:-glycosylation sites. We designated this molecule M160. The domain organization features 12 scavenger receptor cysteine-rich domains followed by a transmembrane region and a cytoplasmic domain that occurs in two forms, a predominant form (M160-alpha) of 71 residues and an alternatively spliced form (M160-ss) of 39 residues. M160-alpha contains three possible phosphorylation sites, which are lost in the alternatively spliced form. RT-PCR analyses showed M160 to be expressed by alveolar macrophages and by the monocyte cell lines HL60, U937, and THP1, but not by Jurkat or Raji cells. Stimulation of U937 cells with phorbol ester resulted in an increased expression of M160 from day 5 onward. RT-PCR analysis of 19 different human tissues showed signals for M160-alpha of varying intensity in all tissues, whereas M160-ss was confined to the spleen. We conclude that M160 is a new member of the scavenger receptor cysteine-rich superfamily expressed by the monocyte/macrophage cell lineage.
Grønlund et al. (Fri,) studied this question.