Cutting edge: CD43 functions as a T cell counterreceptor for the macrophage adhesion receptor sialoadhesin (Siglec-1)

Sialoadhesin (Siglec-1) is a macrophage-restricted sialic acid-binding rece ptor that mediates interactions with hemopoietic cells, including lymphocyt es. In this study, we identify sialoadhesin counterreceptors on T lymphocyt es. Several major glycoproteins (85, 130, 240 kDa) were precipitated by sia loadhesin-Fc fusion proteins from a murine T cell line (TK-1), Binding of s ialoadhesin to these glycoproteins was sialic acid dependent and was abolis hed by mutation of a critical residue (R97A) of the sialic acid binding sit e in the membrane distal Ig-like domain of sialoadhesin, The 130- and 240-k Da sialoadhesin-binding glycoproteins were identified as the sialomucins CD 43 and P-selectin glycoprotein ligand 1 (CD162), respectively, CD43 express ed in COS cells supported increased binding to immobilized sialoadhesin, Fi nally, sialoadhesin hound different glycoforms of CD43 expressed in Chinese hamster ovary cells, including unbranched (core 1) and branched (core 2) O -linked glycans, that are normally found on CD43 in resting and activated T cells, respectively, These results identify CD43 as a T cell counterrecept or for sialoadhesin and suggest that in addition to its anti-adhesive role CD43 may promote cell-cell interactions.