title: Anti-CD9 monoclonal antibodies induce homotypic adhesion of pre-B cell lines by a novel mechanism.
abstract: Anti-CD9 mAb are known agonists of platelet aggregation, but have not been implicated in cell-cell adhesion. We show here in an experimental system that the anti-CD9 mAb 50H.19, ALB6, and BA-2 can induce rapid, and irreversible, homotypic aggregation of the CD9-positive pre-B lymphoblastoid cell lines NALM-6 and HOON, but not of the CD9-negative B cell line Raji. The specificity of the response is indicated by the failure to effect aggregation with mAb directed to CD24, or to HLA class I Ag. The initiation of strong homotypic aggregates of lymphoid cells is a property ascribed to lymphocyte function-associated Ag-1 (LFA-1), a member of the beta 2 subfamily of leukocyte integrins. We show that CD9-induced aggregation is an active process which proceeds at 37 degrees C, but not at 4 degrees C, requires the expenditure of metabolic energy, and a functioning cytoskeleton, and is not inhibited by Arg-Gly-Asp-Ser peptide. These are properties described for LFA-1-mediated aggregation. However, because beta 2-integrins are not expressed on NALM-6 or HOON cells, they are not the mediators of CD9-induced aggregation. In contrast to LFA-1-mediated adhesion which is Mg2+ dependent, CD9-induced adhesion has an absolute requirement for Ca2+, but not Mg2+, indicating that a Ca2(+)-dependent event is sufficient for adhesion. However, Mg2+ enhances adhesion even at optimal concentrations of Ca2+, implicating an additional Mg2(+)-dependent event which requires Ca2+ to be effective. These findings suggest that CD9 Ag regulates a novel mechanism for promoting tight cell-cell adhesion which requires both Ca2+ and Mg2+ for optimal expression.
authors.affiliation: Department of Medicine, University of Alberta, Edmonton, Canada.
authors.forename: A
authors.initials: A
authors.lastname: Masellis-Smith
authors.forename: G S
authors.initials: GS
authors.lastname: Jensen
authors.forename: J G
authors.initials: JG
authors.lastname: Seehafer
authors.forename: J R
authors.initials: JR
authors.lastname: Slupsky
authors.forename: A R
authors.initials: AR
authors.lastname: Shaw
mesh_terms: D000911:Antibodies, Monoclonal / Q000276:immunology*; D015703:Antigens, CD / Q000276:immunology* / Q000502:physiology*; D000943:Antigens, Differentiation / Q000502:physiology*; D002413:Cations, Divalent; D015815:Cell Adhesion Molecules / Q000502:physiology*; D002449:Cell Aggregation; D002460:Cell Line; D003599:Cytoskeleton / Q000502:physiology; D004734:Energy Metabolism; D006801:Humans; D008562:Membrane Glycoproteins; D009842:Oligopeptides / Q000502:physiology; D013696:Temperature; D060245:Tetraspanin 29
chemical_list: D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D000943:Antigens, Differentiation; C554869:CD9 protein, human; D002413:Cations, Divalent; D015815:Cell Adhesion Molecules; D008562:Membrane Glycoproteins; D009842:Oligopeptides; D060245:Tetraspanin 29; C047981:arginyl-glycyl-aspartic acid