Neutrophil myeloperoxidase regulates T-cell-driven tissue inflammation in mice by inhibiting dendritic cell function.

Myeloperoxidase (MPO) is important in intracellular microbial killing by neutrophils but extracellularly causes tissue damage. Its role in adaptive immunity and T-cell-mediated diseases is poorly understood. Here, T-cell responses in lymph nodes (LNs) were enhanced by MPO deletion or in vivo inhibition, causing enhanced skin delayed-type hypersensitivity and antigen (Ag)-induced arthritis. Responses of adoptively transferred OT-II T cells were greater in MPO-deficient than wild-type (WT) recipients. MPO, deposited by neutrophils in LNs after Ag injection, interacted with dendritic cells (DCs) in vivo. Culture of murine or human DCs with purified MPO or neutrophil supernatant showed that enzymatically dependent MPO-mediated inhibition of DC activation occurs via MPO-generated reactive intermediates and involves DC Mac-1. Transfer of DCs cultured with WT, but not MPO-deficient, neutrophil supernatant attenuated Ag-specific immunity in vivo. MPO deficiency or in vivo inhibition increased DC activation in LNs after immunization. Studies with DQ-ovalbumin showed that MPO inhibits Ag uptake/processing by DCs. In vivo DC transfer and in vitro studies showed that MPO inhibits DC migration to LNs by reducing their expression of CCR7. Therefore, MPO, via its catalytic activity, inhibits the generation of adaptive immunity by suppressing DC activation, Ag uptake/processing, and migration to LNs to limit pathological tissue inflammation.

Th1 and Th17 cells induce proliferative glomerulonephritis.

Th1 effector CD4+ cells contribute to the pathogenesis of proliferative and crescentic glomerulonephritis, but whether effector Th17 cells also contribute is unknown. We compared the involvement of Th1 and Th17 cells in a mouse model of antigen-specific glomerulonephritis in which effector CD4+ cells are the only components of adaptive immunity that induce injury. We planted the antigen ovalbumin on the glomerular basement membrane of Rag1(-/-) mice using an ovalbumin-conjugated non-nephritogenic IgG1 monoclonal antibody against alpha3(IV) collagen. Subsequent injection of either Th1- or Th17-polarized ovalbumin-specific CD4+ effector cells induced proliferative glomerulonephritis. Mice injected with Th1 cells developed progressive albuminuria over 21 d, histologic injury including 5.5 +/- 0.9% crescent formation/segmental necrosis, elevated urinary nitrate, and increased renal NOS2, CCL2, and CCL5 mRNA. Mice injected with Th17 cells developed albuminuria by 3 d; compared with Th1-injected mice, their glomeruli contained more neutrophils and greater expression of renal CXCL1 mRNA. In conclusion, Th1 and Th17 effector cells can induce glomerular injury. Understanding how these two subsets mediate proliferative forms of glomerulonephritis may lead to targeted therapies.

Intrarenal antigens activate CD4+ cells via co-stimulatory signals from dendritic cells.

Dendritic cells in the kidney take up antigens, but little is known about their role in providing co-stimulatory signals for the activation of CD4(+) cells. This study examined the phenotype of dendritic cells in the renal interstitium and in the lymph node draining the kidney before and after intrarenal ovalbumin injection. After intrarenal injection of the antigen, expression of the co-stimulatory molecules CD86 and programmed cell death ligand 1 (PD-L1) increased on renal dendritic cells, whereas expression of only CD86 increased on dendritic cells of the draining lymph node. The activation and proliferation of antigen-specific CD4(+) cells in the lymph node were assessed by transfer of naïve, fluorescently labeled ovalbumin-specific T cell receptor transgenic cells to mice before antigen administration. Blocking both CD86 and CD80 profoundly inhibited CD4(+) cell proliferation, but CD86 was the dominant CD28 ligand in the early proliferative response of CD4(+) cells. Conversely, activation of PD-1, the receptor expressed on CD4(+) cells that binds PD-L1 and PD-L2, reduced the proliferation of CD4(+) cells in the draining lymph node. Comparing subcutaneous and intrarenal administration of antigen, it was found that CD4(+) cell activation was slower and the effects of combined CD80 and CD86 blockade were more profound when antigen was presented via the kidney compared with the skin. In summary, renal dendritic cells take up antigen and participate in the control of antigen-specific CD4(+) cell proliferation by upregulating co-stimulatory molecules such as CD86 that stimulate CD4(+) cell proliferation and by signaling through PD-1, which prevents an inappropriately exuberant immune response.

Experimental autoimmune Goodpasture's disease: a pathogenetic role for both effector cells and antibody in injury.

BACKGROUND: Goodpasture's disease [antiglomerular basement membrane (GBM) glomerulonephritis] is a classic autoimmune disease and the only organ-specific autoimmune renal disease in which the antigen is well described. The importance of antibodies against the non-collagenous domain of the alpha3 chain of type IV collagen [alpha3(IV)NC1] is well established. However, observational human studies and studies in experimental systems also imply a role for cell-mediated effector injury. METHODS: Active experimental autoimmune glomerulonephritis (EAG) was induced by immunization with alpha3-alpha5(IV)NC1 heterodimers in B cell intact C57BL/6 mice and B cell (mu chain-deficient) mice. Passive disease was induced by transferring sera from B cell intact and B cell deficient mice with EAG to RAG-1-/- mice (that lack adaptive immunity). Histologic and functional injury was studied. RESULTS: Despite the absence of B cells and immunoglobulin in B-cell-deficient mice, histologic and functional injury developed in mice immunized with alpha3-alpha5(IV)NC1, with T cells and macrophages in glomeruli. Injury occurred to a similar degree to that found in B-cell-intact mice. Transfer of sera from B-cell-intact mice with EAG containing antibodies (but not from B-cell-deficient mice with EAG) to RAG-1-/- mice induced linear immunoglobulin deposits on the glomerular basement membrane (GBM) and pathologic proteinuria. CONCLUSION: Both cell-mediated and humoral effectors are capable of inducing renal injury in EAG. Given the similarity of the disease-initiating antigen in this model to the antigen in human anti-GBM glomerulonephritis, similar overlapping mechanisms are likely to operate in human disease.

Endogenous IL-13 limits humoral responses and injury in experimental glomerulonephritis but does not regulate Th1 cell-mediated crescentic glomerulonephritis.

IL-13 is produced by T helper 2 (Th2) cells, has a role in stimulating Th2-mediated injury, alters humoral responses, and may directly suppress macrophage and neutrophil function. In immune renal disease, the engagement of different effector mediator systems, including humoral and cell-mediated effectors, can result in glomerular injury. Experimental crescentic glomerulonephritis (known as autologous anti-glomerular basement membrane glomerulonephritis) induced by planting an antigen in glomeruli of mice is Th1 directed, delayed-type hypersensitivity (DTH)-like, and antibody independent. To test the hypothesis that, like the counterregulatory Th2 cytokines IL-4 and IL-10, endogenous IL-13 limits effector Th1 responses in glomerulonephritis, crescentic glomerulonephritis was induced in IL-13+/+ and IL-13-/- mice. Although IL-13-/- mice developed increased serum antigen-specific antibody levels, increased glomerular antibody deposition and enhanced switching to the Th1-associated IgG2a subclass, they developed a similar degree of crescentic glomerulonephritis, with similar glomerular T cell/macrophage numbers, renal impairment, and proteinuria. Antigen-specific dermal DTH and IFN-gamma production by antigen-stimulated splenocytes was unaltered. In immune complex (apoferritin-induced) glomerulonephritis, where renal injury is humorally mediated, IL-13-/- mice developed enhanced humoral immune responses and increased proteinuria, with increased IgG2a responses, a more peripheral distribution of immune complexes, but no alterations in leukocyte recruitment. These results demonstrate dissociation of IL-13's effects in antigen induced renal disease with little effect on cellular responses but suppressive effects on humoral effectors and switching to IgG2a. They indicate a role for IL-13 in limiting antibody-mediated renal injury, but not in regulating DTH-like cell-mediated responses in the kidney.

Plasmin is not protective in experimental renal interstitial fibrosis.

BACKGROUND: The plasminogen-plasmin system has potential beneficial or deleterious effects in the context of renal fibrosis. Recent studies have implicated plasminogen activators or their inhibitors in this process. METHODS: The development of renal interstitial fibrosis was studied in mice genetically deficient in plasminogen (plg-/- mice) and littermate controls (plg+/+ mice) by inducing unilateral ureteric obstruction (UUO) by ligating the left ureter. RESULTS: Collagen accumulation in the kidney was decreased in plg-/- mice at 21 days compared with plg+/+ mice by hydroxyproline assay (plg+/+ 19.0 +/- 1.2 microg collagen/mg tissue, plg-/- 15.6 +/- 0.5 microg collagen/mg tissue, P= 0.04). Macrophage accumulation in plg-/- mice was reduced at 21 days, consistent with a role for plasmin in macrophage recruitment in this model. Myofibroblast accumulation, assessed by the expression of alpha-smooth muscle actin (alpha-SMA), was similar in both groups at both time points. Endogenous plasmin played a role in the activation of transforming growth factor-beta (TGF-beta), as plg-/- mice had lower ratios of betaig-h3:TGF-beta1 mRNA than plg+/+ mice. Matrix metalloproteinase (MMP)-9 activity was unchanged in the absence of plasmin, but MMP-2 activity was decreased. CONCLUSION: Plasminogen, the key proenzyme in the plasminogen-plasmin system, does not protect mice from experimental interstitial fibrosis and may have significant pathogenetic effects. These findings, together with other recently published studies in the biology of renal fibrosis, imply that effects of proteins such as plasminogen activator inhibitor-1 (PAI-1), tissue-type plasminogen activator (tPA), and urokinase-type plasminogen activator receptor (uPAR) on renal fibrosis occur independently from the generation of plasmin.

Experimental autoimmune anti-glomerular basement membrane glomerulonephritis: a protective role for IFN-gamma.

IL-12 and IFN-gamma play key roles in murine lupus and planted antigen models of glomerulonephritis. However, their roles in renal organ-specific autoimmunity are unknown. To establish the roles of endogenous IFN-gamma and IL-12 in experimental autoimmune anti-glomerular basement membrane (GBM) glomerulonephritis (EAG), EAG was induced in normal C57BL/6 mice (WT), IL-12p40-deficient (IL-12p40-/-) mice, and IFN-gamma-deficient (IFN-gamma-/-) mice by immunization with alpha3-alpha5(IV)NC1 heterodimers. At 13 wk, WT mice developed EAG with linear mouse anti-GBM antibody deposition, histologic injury, proteinuria, and mild tubulointerstitial disease. Compared with WT mice, IL-12p40-/- mice had decreased histologic injury and trends to decreased leukocyte infiltrates. In contrast, 40% (4 of 10) of IFN-gamma-/- mice developed significant crescent formation and focal or diffuse interstitial infiltrates (WT, 0 of 8). Compared with WT and/or IL-12p40-/- mice, IFN-gamma-/- mice developed increased injury: histologic injury, total glomerular cell numbers, leukocytes in glomeruli, and renal expression of P-selectin and intercellular adhesion molecule 1. All groups developed similar serum anti-alpha3-alpha5(IV)NC1 antibodies and glomerular Ig deposition, but IFN-gamma-/- mice had decreased anti-alpha3-alpha5(IV)NC1 IgG2a. Therefore, IFN-gamma-/- mice developed increased cellular reactants despite a potentially less damaging antibody response. Dermal delayed-type hypersensitivity was increased in alpha3-alpha5(IV)NC1 immunized IFN-gamma-/- mice and was suppressed by recombinant murine IFN-gamma. CD4+ cells from draining nodes of immunized IFN-gamma-/- mice showed increased proportions of proliferating CD4+ cells but similar numbers of apoptotic cells. These studies demonstrate that in renal organ-specific autoimmunity, IL-12 is pathogenetic but IFN-gamma is protective. They lend weight to the hypothesis that depending on the context/severity of the nephritogenic immune response IFN-gamma has different effects.

Plasminogen activator inhibitor-1 is a significant determinant of renal injury in experimental crescentic glomerulonephritis.

Crescentic glomerulonephritis is characterized by glomerular fibrin deposition, and experimental crescentic glomerulonephritis has been shown to be fibrin-dependent. Net fibrin deposition is a balance between activation of the coagulation system causing glomerular fibrin deposition and fibrin removal by the plasminogen-plasmin (fibrinolytic) system. Plasminogen activator inhibitor-1 (PAI-1) inhibits fibrinolysis by inhibiting plasminogen activators and has effects on leukocyte recruitment and matrix deposition. To test the hypothesis that the presence of PAI-1 and its levels were a determinant of injury in crescentic glomerulonephritis, accelerated anti-glomerular basement membrane glomerulonephritis was induced in mice genetically deficient in PAI-1 (PAI-1 -/-), PAI-1 heterozygotes (PAI-1 +/-), and mice engineered to overexpress PAI-1 (PAI-1 tg). Compared with strain-matched genetically normal animals, PAI-1 -/- mice with glomerulonephritis developed fewer glomerular crescents, less glomerular fibrin deposition, fewer infiltrating leukocytes, and less renal collagen accumulation at day 14 of disease. The reduction in disease persisted at day 28, when injury had become more established. In contrast, mice overexpressing the PAI-1 gene (PAI-1 tg), that have basal plasma and renal PAI-1 levels several times, normal developed increased glomerular crescent formation, more glomerular fibrin deposition, increased numbers of infiltrating leukocytes, and more renal collagen at both time points. These studies demonstrate that PAI-1 is a determinant of glomerular fibrin deposition and renal injury in crescentic glomerulonephritis.