Oral interferon-alpha treatment of mice with cryoglobulinemic glomerulonephritis

Therapeutic and Prophylactic Use of Oral, Low-Dose IFNs in Species of Veterinary Interest: Back to the Future

Cytokines are important molecules that orchestrate the immune response. Given their role, cytokines have been explored as drugs in immunotherapy in the fight against different pathological conditions such as bacterial and viral infections, autoimmune diseases, transplantation and cancer. One of the problems related to their administration consists in the definition of the correct dose to avoid severe side effects. In the 70s and 80s different studies demonstrated the efficacy of cytokines in veterinary medicine, but soon the investigations were abandoned in favor of more profitable drugs such as antibiotics. Recently, the World Health Organization has deeply discouraged the use of antibiotics in order to reduce the spread of multi-drug resistant microorganisms. In this respect, the use of cytokines to prevent or ameliorate infectious diseases has been highlighted, and several studies show the potential of their use in therapy and prophylaxis also in the veterinary field. In this review we aim to review the principles of cytokine treatments, mainly IFNs, and to update the experiences encountered in animals.

Synergistic Bcl-2 inhibition by ABT-737 and cyclosporine A

Survival of lymphocytes and melanocyte stem cells critically depends on B cell lymphoma 2 (Bcl-2). In T lymphocytes, a basal calcineurin activity maintains Bcl-2 expression in naïve cells, and the activation of the calcineurin pathway orchestrates the regulation of the intrinsic apoptosis pathway after antigen recognition. Therefore, calcineurin inhibitors might potentiate the pro-apoptotic effect of pharmacological Bcl-2 inhibitors on lymphatic cells. In vitro, a reduced Bcl-2 expression in lymphocytes exposed to calcineurin inhibitors increased their sensitivity to the small molecule Bcl-2 inhibitor ABT-737. This correlated with an augmented pro-apoptotic activity of ABT-737 on lymphocytes in combination with cyclosporine A in naïve mice in vivo. Interestingly, similar processes were observed in melanocytes. ABT-737 induced a fur depigmentation at the site of injection, and this effect was expanded to a generalized depigmentation in combination with cyclosporine A. Thus, inhibiting calcineurin increases the pro-apoptotic potency of ABT-737 in cells depending on Bcl-2 for survival. The increased efficacy of Bcl-2 inhibitors in combination with cyclosporine A might be relevant to exploit their anti-neoplastic and immuno-modulatory properties.

A new function for parietal epithelial cells: a second glomerular barrier

The functional role of glomerular parietal epithelial cells (PECs) remains poorly understood. To test the hypothesis that PECs form an impermeable barrier to filtered protein through the formation of tight junctions (TJ), studies were performed in normal animals and in the anti-glomerular basement membrane (GBM) model of crescentic nephritis. Electron microscopy showed well-defined TJ between PECs in normal mice, which no longer could be identified when these cells became extensively damaged or detached from their underlying Bowman's basement membrane. The TJ proteins claudin-1, zonula occludens-1, and occludin stained positive in PECs; however, staining decreased in anti-GBM disease. To show that these events were associated with increased permeability across the PEC-Bowman's basement membrane barrier, control and diseased animals were injected intravenously with either Texas red-conjugated dextran (3 kDa) or ovalbumin (45 kDa) tracers. As expected, both tracers were readily filtered across the glomerular filtration barrier and taken up by proximal tubular cells. However, when the glomerular filtration barrier was injured in anti-GBM disease, tracers were taken up by podocytes and PECs. Moreover, tracers were also detected between PECs and the underlying Bowman's basement membrane, and in many instances were detected in the extraglomerular space. We propose that together with its underlying Bowman's basement membrane, the TJ of PECs serve as a second barrier to protein. When disturbed following PEC injury, the increase in permeability of this layer to filtered protein is a mechanism underlying periglomerular inflammation characteristic of anti-GBM disease.

Efficient renal recruitment of macrophages and T cells in mice lacking the duffy antigen/receptor for chemokines

The Duffy antigen/receptor for chemokines (DARC) is a chemokine-binding protein that is expressed on erythrocytes and renal endothelial cells. DARC-mediated endothelial transcytosis of chemokines may facilitate the renal recruitment of macrophages and T cells, as has been suggested for neutrophils. We studied the role of Darc in two mouse models of prolonged renal inflammation, one that primarily involves the tubulointerstitium (unilateral ureteral obstruction), and one that requires an adaptive immune response that leads to glomerulonephritis (accelerated nephrotoxic nephritis). Renal expression of Darc and its ligands was increased in both models. Leukocytes effectively infiltrated obstructed kidneys in Darc-deficient mice with pronounced T-cell infiltration at early time points. Development of interstitial fibrosis was comparable in both genotypes. Nephrotoxic nephritis was inducible in Darc-deficient mice, with both an increased humoral immune response and functional impairment during the early phase of disease. Leukocytes efficiently infiltrated kidneys of Darc-deficient mice, with increased cell numbers at early but not late time points. Taken together, renal inflammation developed more rapidly in DARC-deficient mice, without affecting the extent of renal injury at later time points. Thus, genetic elimination of Darc in mice does not prevent the development of renal infiltrates and may even enhance such development during the early phases of interstitial and glomerular diseases in mouse models of prolonged renal inflammation.

Pathogenic mechanisms in membranoproliferative glomerulonephritis

PURPOSE OF REVIEW

This review considers new information on the pathogenesis of a long recognized and poorly understood form of glomerular injury, membranoproliferative glomerulonephritis. This disease has received growing attention as it is the principal renal manifestation of hepatitis C virus infection, which has become pandemic worldwide.

RECENT FINDINGS

This review briefly describes three murine models of membranoproliferative glomerulonephritis suitable for pathogenesis studies. We consider recent evidence implicating innate immune mechanisms in immune and autoimmune-mediated glomerulonephritis, and recent data pointing to the alternative pathway of complement activation in the amplification of glomerulonephritic injury.

SUMMARY

Understanding the contribution of complement activation and innate immunity to the evolution of membranoproliferative glomerulonephritis promises to provide new therapeutic targets for this disease. Inhibitors of the complement cascade are already being tested in clinical trials as therapeutic interventions for some human glomerular diseases. Successful tests of this approach in membranoproliferative glomerulonephritis are still awaited. Our understanding of how the innate immune system modulates glomerulonephritis is still in an early stage, and future studies should be directed at identifying targets and specific interventions that may also benefit patients with this disease.

Chemokine receptor Ccr2 deficiency reduces renal disease and prolongs survival in MRL/lpr lupus-prone mice

MRL/MpJ-Fas(lpr)/J (MRL/lpr) mice represent a well-established mouse model of human systemic lupus erythematosus. MRL/lpr mice homozygous for the spontaneous lymphoproliferation mutation (lpr) are characterized by systemic autoimmunity, massive lymphadenopathy associated with proliferation of aberrant T cells, splenomegaly, hypergammaglobulinemia, arthritis, and fatal immune complex-mediated glomerulonephritis. It was reported previously that steady-state mRNA levels for the chemokine (C-C motif) receptor 2 (Ccr2) continuously increase in kidneys of MRL/lpr mice. For examining the role of Ccr2 for development and progression of immune complex-mediated glomerulonephritis, Ccr2-deficient mice were generated and backcrossed onto the MRL/lpr genetic background. Ccr2-deficient MRL/lpr mice developed less lymphadenopathy, had less proteinuria, had reduced lesion scores, and had less infiltration by T cells and macrophages in the glomerular and tubulointerstitial compartment. Ccr2-deficient MRL/lpr mice survived significantly longer than MRL/lpr wild-type mice despite similar levels of circulating immunoglobulins and comparable immune complex depositions in the glomeruli of both groups. Anti-dsDNA antibody levels, however, were reduced in the absence of Ccr2. The frequency of CD8+ T cells in peripheral blood was significantly lower in Ccr2-deficient MRL/lpr mice. Thus Ccr2 deficiency influenced not only monocyte/macrophage and T cell infiltration in the kidney but also the systemic T cell response in MRL/lpr mice. These data suggest an important role for Ccr2 both in the general development of autoimmunity and in the renal involvement of the lupus-like disease. These results identify Ccr2 as an additional possible target for the treatment of lupus nephritis.

Hyperlipidemia aggravates renal disease in B6.ROP Os/+ mice

INTRODUCTION

Reduction of renal mass is frequently associated with progressive loss of kidney function. We examined the effects of hyperlipidemia on renal pathology and mediators of tissue damage in B6.ROP Os/+ mice, a model of reduced renal mass.

METHODS

C57BL/6 control mice and B6.ROP Os/+ mice were fed normal rodent chow or a high fat, high cholesterol (HFHC) diet for 12 weeks. Kidney function and renal pathology were assessed.

RESULTS

Hyperlipidemia led to a decline in kidney function in C57BL/6 mice. Renal pathology was characterized by an increase in glomerular matrix and cellularity, glomerular and tubulointerstitial macrophage influx, and increased tubular epithelial cell turnover. Chow-fed B6.ROP Os/+ animals demonstrated glomerular hypertrophy with an increase in mesangial matrix and cellularity that was characterized by macrophage influx and increased proliferation. The tubulointerstitium showed increased macrophages as well as tubular atrophy and dilation. Renal pathology was accompanied by an increase in blood urea nitrogen (BUN) and proteinuria. Hyperlipidemia in B6.ROP Os/+ mice resulted in increased plasma BUN compared to chow-fed B6.ROP Os/+ animals and aggravated renal pathology by further increasing glomerular matrix and glomerular hypercellularity. Glomerular hypercellularity was associated with increased expression of platelet-derived growth factor-B (PDGF B) and its receptor beta. Glomerular transforming growth factor-beta (TGF-beta) mRNA expression was increased in B6.ROP Os/+ mice, hyperlipidemic C57BL/6 mice and hyperlipidemic B6.ROP Os/+ animals compared to controls and correlated with the amount of mesangial matrix.

CONCLUSION

This study demonstrates that hyperlipidemia worsens renal pathology in B6.ROP Os/+ mice with a decline in renal function mediated at least in part through increased renal expression of the cytokines PDGF B and TGF-beta.

Overexpression of complement inhibitor Crry does not prevent cryoglobulin-associated membranoproliferative glomerulonephritis

BACKGROUND

Mice overexpressing thymic stromal lymphopoietin (TSLP) develop mixed cryoglobulinemia with renal disease closely resembling human cryoglobulin-associated membranoproliferative glomerulonephritis (MPGN), including glomerular deposits of immunoglobulins and complement. We assessed the effect of complement inhibition through overexpression of Crry (complement receptor-1 related gene/protein Y), which blocks the classic and alternative pathway of complement activation through inhibition of the C3 convertase, in cryoglobulinemia-associated immune complex glomerulonephritis.

METHODS

TSLP transgenic mice were crossbred with animals overexpressing Crry. Mice were sacrificed after 50 days (females) or 120 days (males), and kidneys, blood, and urine were collected from seven mice of each experimental group (wild type, Crry transgenic, TSLP transgenic, and Crry/TSLP doubly transgenic).

RESULTS

TSLP/Crry doubly transgenic animals demonstrated expected serum levels of Crry. Renal involvement, both in TSLP transgenic and TSLP/Crry doubly transgenic animals, was characterized by glomerular matrix expansion, macrophage influx, activation of mesangial cells, and deposition of immunoglobulins and complement. Overexpression of Crry did not result in significant improvement of renal pathology or laboratory findings. Expression of recombinant soluble Crry was confirmed by enzyme-linked immunosorbent assay (ELISA) in Crry transgenic animals. However, formation of the membrane attack complex C5b-9 as a marker of terminal active complement components and represented by glomerular C9 staining could not be inhibited in Crry transgenic TSLP mice.

CONCLUSION

These results indicate that overexpression of Crry was not sufficient to prevent renal injury in TSLP transgenic mice. We suggest that the inhibitory capacity of Crry may be overwhelmed by chronic complement activation. Further studies need to address the role of complement in cryoglobulinemic glomerulonephritis before therapeutic complement inhibition can be attempted.

Deletion of the fcgamma receptor IIb in thymic stromal lymphopoietin transgenic mice aggravates membranoproliferative glomerulonephritis

Engagement of immunoglobulin-binding receptors (FcgammaR) on leukocytes and other cell types is one means by which immunoglobulins and immune complexes activate effector cells. One of these FcgammaRs, FcgammaRIIb, is thought to contribute to protection from autoimmune disease by down-regulation of B-cell responsiveness and myeloid cell activation. We assessed the role of FcgammaRIIb in a mouse model of cryoglobulin-associated membranoproliferative glomerulonephritis induced by overexpression of thymic stromal lymphopoietin (TSLP). TSLP transgenic mice were crossbred with animals deficient for FcgammaRIIb on the same genetic background (C57BL/6). Renal pathology was assessed in female and male animals (wild-type, FcgammaRIIb-/-, TSLP transgenic, and combined TSLP transgenic/FcgammaRIIb-/- mice) after 50 and 120 days, respectively. FcgammaRIIb-/- mice had no significant renal pathology, whereas overexpression of TSLP induced a membranoproliferative glomerulonephritis, as previously established. TSLP transgenic FcgammaRIIb-/- mice appeared sick with increased mortality. Kidney function was significantly impaired in male mice corresponding to aggravated glomerular pathology with increases in glomerular matrix and cellularity. This resulted from both a large influx of infiltrating macrophages and increased cellular proliferation. These results emphasize the important role of FcgammaRIIb in regulating immune responses and suggest that modulation of Fcgamma receptor activation or expression may be a useful therapeutic approach for treating glomerular diseases.