Only mild glomerular abnormalities were observed, in a minority of the glomeruli examined. T cells and macrophages. Y100F-Ig resulted in a similar reduction in the severity of nephritis, but produced no overall reduction in circulating anti-GBM antibodies, although there was a reduction in IgG2a antibodies. We concluded that CD28-B7 blockade reduced autoantibody production and cellular infiltration of glomeruli, and prevented target organ injury. Our results suggest a key role for B7.1 in costimulation of Th1-like autoimmune responses in the rat, and show that glomerular injury in EAG is largely dependent on cell-mediated mechanisms. Introduction Antigen-specific T-cell activation is regulated by a 2-signal pathway. The first signal is provided by engagement of the T-cell receptor (TCR) with the antigenic peptideCMHC molecule complex on Rabbit Polyclonal to CHRNB1 antigen-presenting cells (APC), and thus represents an antigen-specific response. However, this interaction alone is insufficient to induce Fatostatin Hydrobromide optimal T-cell activation without secondary costimulatory signals; these are provided by the binding of specific receptors on T cells with their ligands on APC. The best-characterized and strongest costimulatory signal for interaction between T cells and APC is provided by CD28 and CTLA4 on T cells binding to B7.1 and B7.2 (CD80 and CD86) on APC (1C11). Costimulation via CD28 provides an important signal to antigen-stimulated T cells that results in enhanced activation, proliferation, and differentiation. CTLA4 is a coligand on T cells that also binds to B7.1 and B7.2 on APC, and is believed to deliver a negative signal leading to cell-cycle arrest. Because CTLA4 binds to B7 with greater affinity than does CD28, a soluble form of CTLA4 has been used to inhibit T-cell costimulation via CD28, by blocking B7.1 and B7.2 receptors on APC. Blockade of this pathway has been shown to induce specific T-cell anergy in vitro (3), and to inhibit autoimmune (12C16) and alloimmune responses in vivo. (17). Although studies using the fusion protein CTLA4-Ig, which binds to B7.1 and B7.2, have shown suppression of cell-mediated and humoral immunity in several mouse models of autoimmune disease (12C16), it is unclear whether different costimulatory signals are delivered through CD28 depending on whether B7.1 or B7.2 is the ligand. It has been suggested that B7.1 costimulates T cells for Th1 responses, and B7.2 costimulates T cells for Th2 responses (8C10). CD28-B7 costimulatory blockade by CTLA4-Ig has been shown to prevent experimental autoimmune encephalomyelitis by inhibiting the production of Fatostatin Hydrobromide Th1 cytokines but sparing Th2 cytokines, thus causing a state of immune deviation toward Th2 function (14). However, recent studies using specific B7.1- and B7.2-blocking mAbs to prevent murine autoimmune disease produced varying data regarding to the role of these molecules in the immune response. In experimental autoimmune diabetes, administration of anti-B7.2 mAb ameliorated disease, whereas anti-B7.1 mAb worsened disease (15). The opposite effect was observed in experimental autoimmune encephalomyelitis, where anti-B7.1 mAb was effective at preventing disease, and anti-B7.2 mAb administration was ineffective (16). Greater understanding of the mechanisms by which costimulatory blockade works, and of the different roles of B7.1 and B7.2 in the induction of autoimmunity, is required. Experimental autoimmune glomerulonephritis (EAG) is an experimental model of Goodpastures disease that can be induced in genetically susceptible strains of rat by immunization with heterologous or homologous preparations of glomerular basement membrane (GBM) in adjuvant (18C21). In the model used in this study, Wistar Kyoto (WKY) rats given a single injection of collagenase-solubilized rat GBM in Freunds complete adjuvant (FCA) develop sustained anti-GBM antibody synthesis, linear deposition of IgG on the GBM, deposits of fibrin in the glomeruli, albuminuria, focal necrotizing Fatostatin Hydrobromide glomerulonephritis with crescent formation, and variable lung hemorrhage (21). This model of EAG shares many characteristics with the human disease, and involves anti-GBM antibodies with specificity similar to that of human autoantibodies (22). As in Goodpastures disease, the development of nephritis is associated with both cell-mediated and humoral immunity to the noncollagenous (NC1) domain of the 3 chain of type.