title: Overexpressed Ly-6A.2 mediates cell-cell adhesion by binding a ligand expressed on lymphoid cells.
abstract: The Ly-6 locus encodes several cell surface proteins whose functions are unknown. Although it is hypothesized that these proteins may be receptors, there is no direct evidence that they bind a ligand. Herein we present evidence that Ly-6A.2, a Ly-6 protein expressed on T lymphocytes, binds a ligand expressed on normal thymocytes and splenic B and T cells. We find that transgenic thymocytes that overexpress Ly-6A.2 spontaneously aggregate in culture. This homotypic adhesion requires the overexpression of Ly-6A.2 because it is not observed in cultures of nontransgenic thymocytes. The aggregation of Ly-6A.2 transgenic thymocytes is inhibited by phosphatidylinositol-specific phospholipase C (which removes Ly-6A.2 and other glycosylphosphatidylinositol-anchored proteins from the membrane). Some anti-Ly-6A.2 monoclonal antibodies, including nonactivating ones and Fab' fragments, inhibit this aggregation. In contrast, other anti-Ly-6A.2 monoclonal antibodies increase the aggregation of transgenic but not nontransgenic thymocytes. To further examine whether Ly-6A.2 mediates adhesion (versus inducing another adhesion pathway) reaggregation assays were performed with paraformaldehyde-fixed Tg+ thymocytes. Paraformaldehyde-fixed Tg+ thymocytes reaggregate in culture and this aggregation is also blocked by phosphatidyl-inositol-specific phospholipase C and anti-Ly-6A.2 monoclonal antibodies. These results indicate that the homotypic adhesion of cultured Ly-6A.2 transgenic thymocytes is directly mediated by Ly-6A.2 and, more importantly, strongly suggests that Ly-6A.2 binds a ligand that is expressed on thymocytes. Tg+ thymocytes also bind to nontransgenic thymocytes, B cells, and T cells, indicating that normal cells naturally express the Ly-6A.2 ligand.
authors.affiliation: Dana-Farber Cancer Institute, Boston, MA, USA.
authors.forename: A
authors.initials: A
authors.lastname: Bamezai
authors.forename: K L
authors.initials: KL
authors.lastname: Rock
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D000950:Antigens, Ly / Q000096:biosynthesis* / Q000276:immunology; D001402:B-Lymphocytes / Q000276:immunology / Q000502:physiology*; D002448:Cell Adhesion; D002449:Cell Aggregation; D003433:Crosses, Genetic; D005260:Female; D005434:Flow Cytometry; D015870:Gene Expression; D008024:Ligands; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D054801:Phosphoinositide Phospholipase C; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism; D013154:Spleen / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology / Q000502:physiology*; D013950:Thymus Gland / Q000276:immunology
chemical_list: D000911:Antibodies, Monoclonal; D000950:Antigens, Ly; D008024:Ligands; D010727:Phosphoric Diester Hydrolases; D054801:Phosphoinositide Phospholipase C; D043265:Phosphatidylinositol Diacylglycerol-Lyase