CHARACTERIZATION OF A CD6 LIGAND(S) EXPRESSED ON HUMAN-DERIVED AND MURINE-DERIVED CELL-LINES AND MURINE LYMPHOID-TISSUES

CD6, a type I tell surface glycoprotein expressed predominantly by thy mocytes and mature T lymphocytes, becomes phosphorylated on tyrosine r esidues following T cell activation and has been implicated as an acce ssory molecule in T cell activation. The purpose of this study was to identify cell lines and tissues which express CD6 ligand(s), determine the requirements for CD6 binding, and biochemically characterize the putative CD6 ligand(s). Binding studies with a CD6 immunoglobulin fusi on protein, CD6-Rg, allowed the identification of a number of human ce ll lines which express a CD6 ligand(s). The binding to these cell line s was trypsin sensitive, in part required divalent cations, was blocke d by an anti-CD6 mAb, and could be downregulated by tumor necrosis fac tor alpha (TNF alpha), interleukin-1 beta (IL-1 beta) and interferon-g amma (IFN-gamma). Among the cell lines tested, the human breast carcin oma-derived cell line HBL-100 expressed the highest levels of CD6 liga nd(s) and was used for immunoprecipitation studies. Following metaboli c labeling, CD6-Rg immunoprecipitated glycoproteins of similar to 100, similar to 90, and similar to 45 kDa from HBL-100 cells. Using CD6-Rg we were able to show that murine thymus, lymph nodes. and skin expres s high levels of CD6 ligand(s) and that CD6-Rg bound to a murine thymi c epithelial cell line and to cultured human epidermal keratinocytes. (C) 1994 Academic Press, Inc.