A monoclonal antibody against the 66-kDa protein expressed in mouse spleenand thymus inhibits Ly-6A.2-dependent cell-cell adhesion

The Ly-6 locus encodes several cell surface proteins of 10-12 kDa, Some mem bers of this multigene family may function in cell signaling and/or cell ad hesion processes. T lymphocytes overexpressing Ly-6A.2 (one member of the L y-6 gene family) protein homotypically aggregate when cultured in vitro. Fu rther analysis of this homotypic aggregation suggests that Ly-6A,2 particip ates in cell-cell adhesion. These observations indicated the presence of a Ly-6 ligand(s) on the surface of lymphoid cells. In this study we report ge neration of a hamster mAb, 9AB2, that blocks Ly-6A.2-dependent cell-cell ad hesion. The 9AB2 Ab recognizes a 66-kDa glycoprotein with unique tissue exp ression. The 9AB2 mAb does not bind Ly-6A,2, but coimmunoprecipitates Ly-6A .2 molecule. Moreover, 9AB2 Ag-expressing thymocytes specifically bind to C hinese hamster ovary cells overexpressing Ly-6A,2 protein, and this binding is specifically blocked by 9AB2 and anti-Ly-6A,2 Abs, These results sugges t that the 66-kDa protein recognized by 9AB2 mAb is the putative ligand for Ly-6A.2.