title: CD28 cross-linking augments TCR-mediated signals and costimulates superantigen responses.
abstract: The CD28 molecule expressed on the surface of T cells plays a pivotal role in transducing costimulatory signals necessary for cell activation. CD28 coligation enhances tyrosine phosphorylation and phosphoinositol 3-kinase association in responsive cells. CD28 cross-linking has also been reported to activate inositol phospholipid turnover and to cause release of intracellular calcium. Here we examine the effects of CD28 cross-linking on early activation of protein kinase C (PKC). We have reported recently that either PMA or CD28 cross-linking synergizes with signals delivered by superantigen and cytokines to induce the proliferation of APC-depleted T cells. Unlike PMA, CD28 cross-linking alone failed to induce an increase in membrane-associated PKC activity. However, PKC activation was seen in resting T cells when CD28 was cross-linked in the presence of superantigen plus APC-derived supernatant, which by themselves had no effect on PKC activity. Inhibition of PKC activity using calphostin C blocked the response of pure T cells to superantigen in the presence of either autologous APC, PMA, or CD28 cross-linking. This effect was specific; it was only seen when calphostin C was added within the first hour of stimulation. Assays of [Ca2+]i levels showed that CD28 cross-linking augmented and prolonged the rise in [Ca2+]i induced in T cells by superantigen and APC-derived cytokines. In the presence of superantigen, the proliferative response of T cells costimulated by CD28 cross-linking was cyclosporin A-sensitive, whereas in the presence of PMA, CD28 cross-linking conferred resistance to cyclosporin A. Both the phosphorylation of phospholipase C gamma 1 at tyrosine and the rise in [Ca2+]i induced by CD28 cross-linking in preactivated T cells were blocked by herbimycin A. Herbimycin A treatment also blocked the ability of CD28 cross-linking to induce a rise in [Ca2+]i in resting T cells. We conclude that CD28 costimulatory signals augment superantigen-induced TCR signals by converging onto common TCR effector pathways involving the activation of phospholipase C gamma 1 and PKC and by generating a cyclosporin A-sensitive pathway.
authors.affiliation: Veteran's Administration Medical Center, Memphis, TN 38104.
authors.forename: H
authors.initials: H
authors.lastname: Ohnishi
authors.forename: J A
authors.initials: JA
authors.lastname: Ledbetter
authors.forename: S B
authors.initials: SB
authors.lastname: Kanner
authors.forename: P S
authors.initials: PS
authors.lastname: Linsley
authors.forename: T
authors.initials: T
authors.lastname: Tanaka
authors.forename: A M
authors.initials: AM
authors.lastname: Geller
authors.forename: M
authors.initials: M
authors.lastname: Kotb
mesh_terms: D000938:Antigen-Presenting Cells / Q000276:immunology; D016227:Benzoquinones; D015153:Blotting, Western; D018106:CD28 Antigens / Q000276:immunology* / Q000378:metabolism*; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D016572:Cyclosporine / Q000494:pharmacology; D006801:Humans; D047029:Lactams, Macrocyclic; D008213:Lymphocyte Activation / Q000276:immunology; D009281:Naphthalenes; D011083:Polycyclic Compounds / Q000494:pharmacology; D011233:Precipitin Tests; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D011809:Quinones / Q000494:pharmacology; D011948:Receptors, Antigen, T-Cell / Q000276:immunology; D017828:Rifabutin / Q000031:analogs & derivatives; D015398:Signal Transduction / Q000276:immunology*; D018089:Superantigens / Q000276:immunology*; D013601:T-Lymphocytes / Q000276:immunology*
chemical_list: D016227:Benzoquinones; D018106:CD28 Antigens; D047029:Lactams, Macrocyclic; D009281:Naphthalenes; D011083:Polycyclic Compounds; D011809:Quinones; D011948:Receptors, Antigen, T-Cell; D018089:Superantigens; D017828:Rifabutin; D000001:Calcimycin; C020754:herbimycin; D016572:Cyclosporine; D011505:Protein-Tyrosine Kinases; D011493:Protein Kinase C; C058819:calphostin C; D002118:Calcium