Alexander R. Rosenkranz

P-selectin deficiency exacerbates experimental glomerulonephritis: a protective role for endothelial P-selectin in inflammation

P-selectin is a leukocyte adhesion receptor present in endothelial cells and platelets. We examined the role of P-selectin in the autologous phase of an accelerated model of anti-glomerular basement membrane (GBM) glomerulonephritis using P-selectin-deficient mice and chimeric mice expressing P-selectin only in platelets or endothelial cells. P-selectin-deficient mice exhibited more severe glomerular damage with increased interstitial mononuclear leukocytic infiltrates, and had significantly increased proteinuria and mortality when compared to wild-type mice. P-selectin on the endothelium was predominantly responsible for protection from the exacerbated disease, because chimeric mice with endothelial P-selectin, and not mice with platelet P-selectin, showed glomerular injury similar to that in wild-type animals. Levels of soluble circulating P-selectin were increased in nephritic wild-type mice and in chimeric mice with endothelial P-selectin, but not platelet P-selectin. Levels of soluble P-selectin, which has been shown to be anti-inflammatory in vitro, were inversely associated with the severity of disease. P-selectin was not expressed in the endothelium of the glomerulus or interstitium. Thus, the protective effect in wild-type mice may be accounted for, in part by soluble P-selectin shed by non-renal endothelial cells, although other endothelial P-selectin-dependent mechanisms cannot be ruled out.

Nonphlogistic Clearance of Late Apoptotic Neutrophils by Macrophages: Efficient Phagocytosis Independent of β2 Integrins

Neutrophils undergo constitutive death by apoptosis, leading to safe nonphlogistic phagocytosis and clearance by macrophages. Recent work has shown that before secondary necrosis, neutrophils exhibiting classical features of apoptosis can progress to a morphologically defined late apoptotic state. However, whether such neutrophils could be safely cleared was unknown. We now report that human late apoptotic neutrophils could be purified from cultured neutrophil populations undergoing constitutive death and were subsequently ingested by human monocyte-derived macrophages by serum-independent mechanisms that did not trigger the release of IL-8 or TNF-α. Such ingestion was specifically inhibited by Abs to thrombospondin-1 and the αvβ3 vitronectin receptor. Murine bone marrow-derived macrophage phagocytosis of late and early apoptotic neutrophils occurred by similar mechanisms, proceeding with the same efficiency as that observed for wild-type controls when macrophages from αm−/− or β2−/− mice were used. We conclude that specific nonphlogistic, β2 integrin-independent mechanisms involving thrombospondin-1 and αvβ3 allow macrophages to ingest late apoptotic neutrophils without eliciting inflammatory cytokine secretion.

Role of mast cells in experimental anti-glomerular basement membrane glomerulonephritis.

Recently, divergent reports on the role of mast cells (MC) in different glomerular diseases have brought our attention to their role in an accelerated model of anti‐glomerular basement membrane (GBM) glomerulonephritis (GN). Genetically MC‐deficient KitW/KitW‐v mice, MC‐reconstituted KitW/KitW‐v mice and Kit+/+ control mice were subjected to anti‐GBM GN. Kit+/+ mice developed moderate proteinuria and glomerular damage following the induction of anti‐GBM nephritis. In contrast, proteinuria and glomerular damage were dramatically increased in MC‐deficient KitW/KitW‐v mice. MC‐reconstituted KitW/KitW‐v mice showed proteinuria and glomerular damage comparable to Kit+/+ mice. A significant increase in infiltrating T cells and macrophages was detected in MC‐deficient KitW/KitW‐v mice as compared to Kit+/+ control mice and MC‐reconstituted KitW/KitW‐v mice. Accordingly, we observed an increase of TGF‐β1 mRNA in kidneys from KitW/KitW‐v mice. Interestingly, we did not detect MC in the kidney using either Giemsa staining or RT‐real‐time PCR, but MC were found in the regional lymph nodes. Finally, mortality of KitW/KitW‐v mice was significantly increased after the induction of anti‐GBM GN due to uremia. Our report provides the first direct evidence that MC are protective in anti‐GBM GN, possibly by modulating the influx of effector T cells and macrophages to inflammatory sites in the kidney.

Pathogenic role of P-selectin in experimental cerebral malaria: importance of the endothelial compartment.

P-selectin is a leukocyte adhesion receptor expressed on the surface of activated platelets and endothelial cells. Its role in the pathogenesis of cerebral malaria was explored in a murine model of cerebral malaria. Infection of mice with Plasmodium berghei ANKA led to P-selectin up-regulation in brain vessels of cerebral malaria-susceptible mice but not of cerebral malaria-resistant mice. Treatment of susceptible mice with anti-mouse P-selectin mAb failed to prevent the development of the neurological syndrome. However, P-selectin-deficient mice infected with Plasmodium berghei ANKA had a cumulative incidence of cerebral malaria which was significantly reduced compared to wild-type animals (4.5% versus 80%, respectively), despite identical levels of parasitemia, platelet and leukocyte accumulation. To determine whether P-selectin on platelets and/or endothelium was responsible for the microvascular pathology, cerebral malaria was assessed in chimeric mice deficient in platelet or endothelial P-selectin, which were generated by bone marrow transplantation. Mice deficient only in endothelial P-selectin did not show any sign of cerebral malaria (vascular plugging, hemorrhages, or edema), while mice lacking only platelet P-selectin showed signs of cerebral malaria similar to that seen in wild-type mice. These results indicate that endothelial P-selectin plays an important role in the pathogenesis of cerebral malaria.

Atorvastatin attenuates murine anti-glomerular basement membrane glomerulonephritis

Statins mediate many of their protective effects by lowering lipids as well as by modulating inflammation. Here, we studied their potential immunomodulatory role in renal inflammation using an autoimmune mouse model of anti-glomerular basement membrane glomerulonephritis. Oral treatment with Atorvastatin dramatically reduced albuminuria and histological changes in the kidneys as compared to vehicle-treated control animals. There was a significant decrease in the Th1 and Th17 response in the regional lymph nodes draining the kidneys. This systemic effect was accompanied by decreased infiltration of the kidneys with inflammatory CD4(+) T and Th17 cells, macrophages, and neutrophils in statin-treated mice. Regulatory T cells were not altered in their number, FoxP3 expression, or suppressive capacity, but their interleukin-10 production was significantly increased by statin treatment. Hence, Atorvastatin systemically and locally decreased the Th1 and Th17 response, thereby protecting the mice against anti-glomerular basement membrane glomerulonephritis. Whether statins can be used to treat human autoimmune renal diseases will require more direct studies.

Basophils and mast cells in renal injury

Until recently, basophils and mast cells were considered mainly effector cells with an innate immune response linked to allergy and parasite infection. Only in the past few years they were recognized as important regulators of adaptive immunity. The development of new methods and reagents has enabled detection and functional analysis of these rare cells in patients and murine disease models. Basophils are normally present in the peripheral blood, spleen, and bone marrow, but migrate into lymph nodes and tissues during inflammation. They are rapidly activated by cytokines (e.g., interleukin (IL)-3) and intact antigens that cross-link surface-bound immunoglobulins. Activated basophils change the phenotype of T cells toward Th2 and markedly support humoral memory responses. Mast cells also migrate into lymph nodes and interact with dendritic cells, T cells, and B cells. In this review, we describe how mast cells and basophils affect immune responses and discuss implications for renal diseases and transplant rejection.

Regulatory interactions of αβ and γλ T cells in glomerulonephritis

BACKGROUNDnSeveral lines of evidence suggest that cellular immune mechanisms contribute to glomerulonephritis.nnnMETHODSnThe roles of alphabeta and gammadelta T cells in the pathogenesis of glomerulonephritis were investigated in a model of nephrotoxic nephritis in mice deficient in either T-cell population [T-cell receptor (TCR)beta and TCRdelta knockout mice]. The model, induced by the injection of rabbit anti-mouse glomerular basement membrane antibody, is characterized by the development of proteinuria and glomerular damage over a 21-day observation period in wild-type mice.nnnRESULTSnMice deficient in either alphabeta or gammadelta T cells developed minimal proteinuria and glomerular lesions and had a significant reduction in macrophage accumulation compared with wild-type mice. In gammadelta T-cell-deficient mice, circulating levels and glomerular deposition of autologous IgG were comparable to wild-type levels, while alphabeta T-cell-deficient mice had no autologous IgG production. Autologous antibody production was not required for the development of glomerulonephritis since mice that lack IgG and B cells (micro-chain-/-) developed similar proteinuria to that observed in wild-type mice.nnnCONCLUSIONSnThese studies suggest a proinflammatory role for both alphabeta and gammadelta T cells in glomerular injury, independent of the humoral response. This is the first demonstration, to our knowledge, that both T-cell subsets contribute to the progression of a disease, and it suggests that complex regulatory interactions between alphabeta and gammadelta T cells play a role in glomerular injury.

Regulatory interactions of alphabeta and gammadelta T cells in glomerulonephritis.

BACKGROUNDnSeveral lines of evidence suggest that cellular immune mechanisms contribute to glomerulonephritis.nnnMETHODSnThe roles of alphabeta and gammadelta T cells in the pathogenesis of glomerulonephritis were investigated in a model of nephrotoxic nephritis in mice deficient in either T-cell population [T-cell receptor (TCR)beta and TCRdelta knockout mice]. The model, induced by the injection of rabbit anti-mouse glomerular basement membrane antibody, is characterized by the development of proteinuria and glomerular damage over a 21-day observation period in wild-type mice.nnnRESULTSnMice deficient in either alphabeta or gammadelta T cells developed minimal proteinuria and glomerular lesions and had a significant reduction in macrophage accumulation compared with wild-type mice. In gammadelta T-cell-deficient mice, circulating levels and glomerular deposition of autologous IgG were comparable to wild-type levels, while alphabeta T-cell-deficient mice had no autologous IgG production. Autologous antibody production was not required for the development of glomerulonephritis since mice that lack IgG and B cells (micro-chain-/-) developed similar proteinuria to that observed in wild-type mice.nnnCONCLUSIONSnThese studies suggest a proinflammatory role for both alphabeta and gammadelta T cells in glomerular injury, independent of the humoral response. This is the first demonstration, to our knowledge, that both T-cell subsets contribute to the progression of a disease, and it suggests that complex regulatory interactions between alphabeta and gammadelta T cells play a role in glomerular injury.

Leukocyte-Endothelial Cell Interactions – Lessons from Knockout Mice

The advent of gene targeting has led to the generation of several mouse strains deficient in select leukocyte adhesion receptors. These strains of mice have been very informative about the roles of cell adhesion molecules in leukocyte-endothelium interaction and have produced some surprises: roles for leukocyte adhesion receptors have been demonstrated in development as well as pathologies like obesity, and evidence for functional synergies between adhesion receptors have been provided. We attempt in this review to first outline the technique of gene targeting and give an overview of leukocyte adhesion receptors and mice deficient in these receptors. Second, we discuss models of experimental glomerulonephritis and what we have learned about leukocyte adhesion receptors in the pathogenesis of glomerulonephritis through studies in knockout mice.

Glomerular inflammation: use of genetically deficient mice to elucidate the roles of leukocyte adhesion molecules and Fc-gamma receptors in vivo.

Single gene knock-outs in mice have been used to define the biological role of leukocyte adhesion receptors, Fc-gamma receptors and complement in animal models of immune complex glomerulonephritis. These studies have shown important differences in the role of P-selectin in glomerular inflammation and inflammation at other sites, and have given a new appreciation of the dominant role played by Fc-gamma receptors in immune complex-induced glomerular injury.