A NOVEL LIGAND FOR CD44 IS SERGLYCIN, A HEMATOPOIETIC-CELL LINEAGE-SPECIFIC PROTEOGLYCAN - POSSIBLE INVOLVEMENT IN LYMPHOID-CELL ADHERENCE AND ACTIVATION

The lymphocyte adhesion molecule CD44 recognizes a non-hyaluronate pro teoglycan, gp600, secreted by mouse T cell line CTLL2. We now demonstr ate that gp600 is identical to serglycin, a member of the small proteo glycan family stored in intracellular secretory granules of lymphoid, myeloid, and some tumor cells. Purified gp600 has the ability to bind specifically to CD44, and the binding is dependent on activation of CD 44. The CD44-binding elements on gp600 or serglycin are glycosaminogly cans consisting of chondroitin 4-sulfate. Serglycin is readily exocyto sed, and its interaction with active form CD44 augments the CDS depend ent degranulation of CD44 positive CTL clones. We conclude that the se rglycin secreted from secretory granules of hematopoietic cells is a n ovel ligand for CD44, and could regulate lymphoid cell adherence and a ctivation.