title: Superantigen and HLA-DR ligation induce phospholipase-C gamma 1 activation in class II+ T cells.
abstract: Bacterial enterotoxin superantigens bind directly to HLA class II molecules (HLA-DR) expressed on both APC and activated human T cells, and simultaneously bind to certain V beta chains of the TCR. In this report, we compared early T cell signaling events in human alloantigen-stimulated T cells when activated by HLA-DR ligation through antibody cross-linking or by direct enterotoxin superantigen binding. Both types of stimuli induced tyrosine phosphorylation of phosphatidylinositol-specific phospholipase C gamma 1 (PLC gamma 1) and an increase in intracellular calcium concentration; however, superantigen-induced signaling was stronger than class II ligation alone. Antibody-mediated ligation of HLA-DR with CD3 resulted in augmented PLC gamma 1 activation and increased calcium mobilization, consistent with a mechanism of superantigen activity through a combination of class II and CD3/Ti signals. In addition, down-modulation of CD3 receptors with antibody demonstrated that superantigen-induced signaling events were CD3-dependent. Superantigen signaling was also class II-dependent, in that resting T cells were not responsive to direct enterotoxin stimulation. To address how early signal transducing activity correlated with T cell responsiveness, alloantigen-primed T cells were activated with immobilized class II-specific mAb or soluble superantigen. Both HLA-DR mAb-stimulated T cells and enterotoxin-treated T cells proliferated strongly in response to co-stimulation by a combination of CD28 receptor engagement and PMA addition. In addition, superantigen-induced growth was induced by CD28 receptor ligation with antibody or the B7 counter-receptor expressed on Chinese hamster ovary cells. Taken together, these results indicate that class II molecules expressed on activated T cells are directly coupled to the PLC gamma 1 signal transduction pathway, and that coligation of HLA-DR with CD3 augments T cell signaling comparable to that induced by enterotoxin superantigen. Thus, we suggest that superantigen-induced early signaling responses in activated T cells may be due in part to class II transmembrane signals induced when HLA-DR and V beta are ligated in cis.
authors.affiliation: Bristol-Myers Squibb Pharmaceutical Research Institute, Seattle, WA 98121.
authors.forename: S B
authors.initials: SB
authors.lastname: Kanner
authors.forename: N
authors.initials: N
authors.lastname: Odum
authors.forename: L
authors.initials: L
authors.lastname: Grosmaire
authors.forename: S
authors.initials: S
authors.lastname: Masewicz
authors.forename: A
authors.initials: A
authors.lastname: Svejgaard
authors.forename: J A
authors.initials: JA
authors.lastname: Ledbetter
mesh_terms: D000942:Antigens, Bacterial / Q000276:immunology*; D015703:Antigens, CD / Q000276:immunology; D000945:Antigens, Differentiation, T-Lymphocyte / Q000276:immunology; D018106:CD28 Antigens; D004768:Enterotoxins / Q000276:immunology*; D004789:Enzyme Activation; D006681:HLA-D Antigens / Q000276:immunology*; D006801:Humans; D066298:In Vitro Techniques; D008213:Lymphocyte Activation; D019000:Phosphotyrosine; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D013211:Staphylococcus aureus / Q000276:immunology; D013601:T-Lymphocytes / Q000201:enzymology* / Q000276:immunology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D010738:Type C Phospholipases / Q000378:metabolism*; D014443:Tyrosine / Q000031:analogs & derivatives / Q000378:metabolism
chemical_list: D000942:Antigens, Bacterial; D015703:Antigens, CD; D000945:Antigens, Differentiation, T-Lymphocyte; D018106:CD28 Antigens; D004768:Enterotoxins; D006681:HLA-D Antigens; D019000:Phosphotyrosine; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; D010738:Type C Phospholipases; D013755:Tetradecanoylphorbol Acetate