A thymocyte-activating factor derived from glomerular mesangial cells

The glomerular mesangium is centrally involved in immune-mediated glomerulonephritis. The mesangial cell is a mesenchyme-derived multipotential vascular pericyte, which shares several properties with macrophages. Cultured, proliferating rat mesangial cells produce a factor, mesangial cell-derived thymocyte-activating factor (MC-TAF), which physicochemically and biologically closely resembles macrophage interleukin 1. MC-TAF is heat labile, of low m.w. (approximately 15,000), and adheres to anion exchangers. MC-TAF acts to augment lectin-induced thymocyte proliferation and enhances peripheral lymphocyte production of interleukin 2. These findings suggest that a mesangial cell cytokine may interact with the cellular immune system in an antigenically nonspecific fashion to modulate immune responses in glomerular disease.     

The cytokine language of monocytes and macrophages in systemic sclerosis

Many important observations suggest monocyte/macrophage involvement in systemic sclerosis (SSc). A high concentration of immune mediators, such as IL-6, IL-10 and IL-13, the infiltration of mononuclear cells in affected organs and the production of autoantibodies suggest that immune system dysfunction drives SSc pathogenesis. The recently reported study by Higashi-Kuwata and colleagues, in light of other observations, provides further insight into activation of macrophages/monocytes in SSc patients, suggesting that these cells undergo distinct activation pathways. These results emphasize the need for more detailed analyses of the several markers now defined in SSc peripheral blood mononuclear cells and tissues to better define the cytokine language speaking to monocytes/macrophages in SSc that promote vascular injury and tissue fibrosis.     

The light and the dark sides of Interleukin-10 in immune-mediated diseases and cancer.

Interleukin-10 (IL-10) is known to be a tolerogenic cytokine since it inhibits pro-inflammatory cytokine production and T cell stimulatory capacities of myeloid cells, such as macrophages and dendritic cells. In particular, it has a non-redundant tolerogenic role in intestinal immune homeostasis, since mice and patients with genetic defects in the IL-10/IL-10R pathway develop spontaneously colitis in the presence of a normal intestinal flora. However, IL-10 is also a growth and differentiation factor for B-cells, can promote autoantibody production and has consequently a pathogenic role in systemic lupus erythematosus. Moreover, IL-10 can promote cytotoxic T-cell (CTL) responses and this immunogenic activity might be relevant in type-1 diabetes and anti-tumor immune responses. This review summarizes these paradoxic effects of IL-10 on different types of immune responses, and proposes that different cellular sources of IL-10, in particular IL-10-secreting helper and regulatory T-cells, have different effects on B-cell and CTL responses. Based on this concept we discuss the rationales for targeting the IL-10 pathway in immune-mediated diseases and cancer.     

Inhibition of mesangial cell nitric oxide in MRL/lpr mice by prostaglandin J2 and proliferator activation receptor-gamma agonists

MRL/Mp-lpr/lpr (MRL/lpr) mice develop immune complex glomerulonephritis similar to human lupus. Glomerular mesangial cells are key modulators of the inflammatory response in lupus nephritis. When activated, these cells secrete inflammatory mediators including NO and products of cyclooxygenase perpetuating the local inflammatory response. PGJ2, a product of cyclooxygenase, is a potent in vitro inhibitor of macrophage inflammatory functions and is postulated to function as an in vivo inhibitor of macrophage-mediated inflammatory responses. We hypothesized that in lupus, a defect in PGJ2 production allows the inflammatory response to continue unchecked. To test this hypothesis, mesangial cells were isolated from MRL/lpr and BALB/c mice and stimulated with IL-1beta or LPS plus IFN-gamma. In contrast to the 2- to 3-fold increase in PGJ2 production by stimulated BALB/c mesangial cells, supernatant PGJ2 did not increase in MRL/lpr mesangial cell cultures. NO production in stimulated MRL/lpr and BALB/c mesangial cells, was blocked by PGJ2 and pioglitazone. These studies suggest that abnormalities in PGJ2 production are present in MRL/lpr mice and may be linked to the heightened activation state of mesangial cells in these mice.     

Cutting edge: Calcium/Calmodulin-dependent protein kinase type IV is essential for mesangial cell proliferation and lupus nephritis

Renal involvement in systemic lupus erythematosus remains a major cause of morbidity and mortality. Although immune parameters that instigate renal damage have been characterized, their link to local processes, which execute tissue damage, is poorly understood. Using genetic-deletion and pharmacological-inhibition approaches, we demonstrated that calcium/calmodulin-dependent protein kinase type IV, which contributes to altered cytokine production in systemic lupus erythematosus patients, controls spontaneous and platelet-derived growth factor-stimulated mesangial cell proliferation and promotes IL-6 production through AP-1. Our studies identified calcium/calmodulin-dependent protein kinase type IV as a valuable treatment target for lupus nephritis and point out the importance of local kidney factors in the expression of tissue damage that, if properly targeted, should enhance clinical benefit and limit toxicity.     

Conditioned medium from alternatively activated macrophages induce mesangial cell apoptosis via the effect of Fas

During inflammation in the glomerulus, the proliferation of myofiroblast-like mesangial cells is commonly associated with the pathological process. Macrophages play an important role in regulating the growth of resident mesangial cells in the glomeruli. Alternatively activated macrophage (M2 macrophage) is a subset of macrophages induced by IL-13/IL-4, which is shown to play a repair role in glomerulonephritis. Prompted by studies of development, we performed bone marrow derived macrophage and rat mesangial cell co-culture study. Conditioned medium from IL-4 primed M2 macrophages induced rat mesangial cell apoptosis. The pro-apoptotic effect of M2 macrophages was demonstrated by condensed nuclei stained with Hoechst 33258, increased apoptosis rates by flow cytometry analysis and enhanced caspase-3 activation by western blot. Fas protein was up-regulated in rat mesangial cells, and its neutralizing antibody ZB4 partly inhibited M2 macrophage-induced apoptosis. The up-regulated arginase-1 expression in M2 macrophage also contributed to this apoptotic effect. These results indicated that the process of apoptosis triggered by conditioned medium from M2 macrophages, at least is partly conducted through Fas in rat mesangial cells. Our findings provide compelling evidence that M2 macrophages control the growth of mesangial cells in renal inflammatory conditions.     

Glomerular mesangial cells in local inflammation. Induction of the expression of MHC class II antigens by IFN-gamma

Glomerular mesangial cells (MC) were isolated from rats and cultured for a prolonged period of time, resulting in a homogeneous cell population. MC were characterized as belonging to the smooth muscle type. They were negative for MHC class II expression. IFN-gamma and TNF alpha suppressed the proliferation of MC, demonstrating receptors for these cytokines on MC. IFN-gamma or TNF alpha, respectively, enhanced basal MHC class I Ag expression of proliferating cells in culture. The combination of the two cytokines yielded stronger effects. IL-1 beta was ineffective in enhancing MHC class I Ag expression, although MC possessed receptors for this cytokine. IFN-gamma dose dependently induced the expression of MHC class II Ag, while TNF alpha or IL-1 beta were ineffective alone. The combination of IFN-gamma with TNF alpha or IL-1 beta resulted in an enhanced induction of MHC class II Ag, compared to IFN-gamma administration alone. These findings suggest that proliferating mesangial cells of the smooth muscle type may participate in local inflammatory responses or substitute for macrophages by meeting the accessory cell requirement in the interaction with T lymphocytes. Furthermore, the data have important implications for the evaluation of the role of mesangial cells in autoimmune disease of the kidney.     

C-reactive protein functions as a negative regulator of macrophage activation induced by apoptotic DNA

C-reactive protein (CRP), an acute-phase protein with an ability to bind to nuclear antigen, has been reported to regulate cytokine secretion and modulate immune responses. We previously reported that activated syngeneic lymphocyte-derived apoptotic DNA (apopDNA) could induce macrophage activation and contribute to the initiation and progression of lupus nephritis. It is reasonable to hypothesize that CRP might regulate apopDNA-induced macrophage activation. Herein, CRP was shown to promote macrophage-mediated apopDNA uptake by binding to apopDNA (CRP/apopDNA complex). Notably, CRP/apopDNA treatment inhibited the production of inflammatory cytokines and chemokines by macrophages which could be induced by apopDNA alone. Further coculture and transwell studies revealed that CRP/apopDNA-induced macrophages prohibited apopDNA-induced macrophage activation in an IL-10 dependent manner. These results provide insight into the potential mechanism of CRP regulatory activity in macrophage activation induced by apopDNA in the context of lupus nephritis and other autoimmune diseases.     

Enhanced apoptotic cell clearance capacity and B cell survival factor production by IL-10-activated macrophages: implications for Burkitt's lymphoma

Burkitt's lymphoma (BL) is typified by frequent tumor cell apoptosis and significant macrophage infiltration. Since BL cells have an inherent tendency to undergo apoptosis at a high rate, we reasoned that macrophages in BL are functionally enhanced in at least two activities that have implications for tumor pathogenesis: 1) engulfment of apoptotic cells, an anti-inflammatory process known to suppress immune responses, and 2) production of BL cell survival factors that limit the extent of tumor cell apoptosis. In this study, we show that the microenvironment of BL is rich in the pleiotropic cytokine IL-10, which can be produced by both tumor cells and macrophages, and that IL-10-activated human macrophages have enhanced capacity to engulf apoptotic cells in vitro. This was found to be dependent on the macrophage tethering receptor of apoptotic cells, CD14. Furthermore, IL-10-activated macrophages were found to produce markedly higher levels of the B cell survival factor, B cell-activating factor of the TNF family/B lymphocyte stimulator (BAFF/BLyS) than macrophages matured in the absence of IL-10. Coculture of macrophages with BL cells further enhanced BAFF secretion. Significantly, we show that enhancement of BL cell survival by IL-10-activated macrophages is mediated by a BAFF-dependent component and that BAFF is produced at high levels by tumor-associated macrophages in situ. These results indicate that macrophages, regulated by IL-10, have the potential to promote BL pathogenesis, first, through suppression of antitumor immunity following enhanced engulfment of apoptotic tumor cells and, second, through increased production of tumor cell growth/survival factors.     

Renal cyclo-oxygenase and lipoxygenase products in health and disease

Renal glomeruli have cyclo-oxygenase and lipoxygenase enzymes which convert arachidonic acid to prostaglandins, thromboxane and 12-hydroxyeicosatetraenoic acid. Glomerular epithelial and mesangial cells, in culture, also synthesize these arachidonate products. Angiotensin and vasopressin contract mesangial cells and stimulate mesangial synthesis of PGE2. PGE2, in the glomerulus, antagonizes the actions of angiotensin on the mesangium and hence reduces angiotensin-mediated glomerular contraction. Glomerular immune injury (nephrotoxic serum nephritis) augments glomerular production of prostaglandins and thromboxane. Thromboxane reduces glomerular function and inhibition of thromboxane synthesis preserves glomerular filtration rate and renal plasma flow in this disease model. Spontaneously hypertensive rats also have enhanced glomerular prostaglandin and thromboxane synthesis. Although acute inhibition of thromboxane synthesis will vasodilate the hypertensive rat kidney, chronic inhibition does not reduce blood pressure or increase renal blood flow.     

Dual roles of immune cells and their factors in cancer development and progression

Traditional wisdom holds that intact immune responses, such as immune surveillance or immunoediting, are required for preventing and inhibiting tumor development; but recent evidence has also indicated that unresolved immune responses, such as chronic inflammation, can promote the growth and progression of cancer. Within the immune system, cytotoxic CD8(+) and CD4(+) Th1 T cells, along with their characteristically produced cytokine IFN-γ, function as the major anti-tumor immune effector cells, whereas tumor associated macrophages (TAM) or myeloid-derived suppressive cells (MDSC) and their derived cytokines IL-6, TNF, IL-1β and IL-23 are generally recognized as dominant tumor-promoting forces. However, the roles played by Th17 cells, CD4(+) CD25(+) Foxp3(+) regulatory T lymphocytes and immunoregulatory cytokines such as TGF-β in tumor development and survival remain elusive. These immune cells and the cellular factors produced from them, including both immunosuppressive and inflammatory cytokines, play dual roles in promoting or discouraging cancer development, and their ultimate role in cancer progression may rely heavily on the tumor microenvironment and the events leading to initial propagation of carcinogenesis.     

Activation of macrophages and the intestinal immune system by an orally administered decoction from cultured mycelia of Cordyceps sinensis

The effects of an orally administered hot-water extract (HW) from cultured mycelia of Cordyceps sinensis on the activation of macrophages and the intestinal immune system were studied in mice. The general composition of HW was 83.9% carbohydrate, 11.8% protein, 1.9% lipid and 2.4% ash, and the carbohydrates were mainly composed of glucose, mannose, galactose and arabinose (molar ratio of 1.0:0.8:0.5:0.1). HW stimulated the activation (1.7-fold of the saline control) of macrophages and IL-6 production (1.5-fold) at 2.0 g/kg/day. Analyzing the culture supernatant of Peyer's patch cells from C3H/HeJ mice that had been fed with HW at 1.0 g/kg/day for 7 days indicated that the bone marrow cells had significantly proliferated (1.9-fold). In addition, the amounts of GM-CSF and IL-6 in the culture supernatant of Peyer's patch cells at the same dose were significantly increased (1.8-fold and 2.2-fold, respectively). These results indicate that an oral administration of HW may modulate IL-6 production by the activation of macrophages, and also enhance the secretion of hematopoietic growth factors such as GM-CSF and IL-6 from Peyer's patch cells. Since such cytokines as GM-CSF and IL-6 from Peyer's patch cells act on the systemic immune system, it can be assumed that orally administered HW modulated not only the local but also systemic immune system.     

Tacaribe virus but not junin virus infection induces cytokine release from primary human monocytes and macrophages

The mechanisms underlying the development of disease during arenavirus infection are poorly understood. However, common to all hemorrhagic fever diseases is the involvement of macrophages as primary target cells, suggesting that the immune response in these cells may be of paramount importance during infection. Thus, in order to identify features of the immune response that contribute to arenavirus pathogenesis, we have examined the growth kinetics and cytokine profiles of two closely related New World arenaviruses, the apathogenic Tacaribe virus (TCRV) and the hemorrhagic fever-causing Junin virus (JUNV), in primary human monocytes and macrophages. Both viruses grew robustly in VeroE6 cells; however, TCRV titres were decreased by approximately 10 fold compared to JUNV in both monocytes and macrophages. Infection of both monocytes and macrophages with TCRV also resulted in the release of high levels of IL-6, IL-10 and TNF-α, while levels of IFN-α, IFN-β and IL-12 were not affected. However, we could show that the presence of these cytokines had no direct effect on growth of either TCRV of JUNV in macrophages. Further analysis also showed that while the production of IL-6 and IL-10 are dependent on viral replication, production of TNF-α also occurs after exposure to UV-inactivated TCRV particles and is thus independent of productive virus infection. Surprisingly, JUNV infection did not have an effect on any of the cytokines examined indicating that, in contrast to other viral hemorrhagic fever viruses, macrophage-derived cytokine production is unlikely to play an active role in contributing to the cytokine dysregulation observed in JUNV infected patients. Rather, these results suggest that an early, controlled immune response by infected macrophages may be critical for the successful control of infection of apathogenic viruses and prevention of subsequent disease, including systemic cytokine dysregulation.     

Interleukin-10-induced neutrophil gelatinase-associated lipocalin production in macrophages with consequences for tumor growth

Tumor cell-derived factors, such as interleukin 10 (IL-10), polarize macrophages toward a regulatory M2 phenotype, characterized by the expression of anti-inflammatory cytokines and protumorigenic mediators. Here we explored molecular mechanisms allowing IL-10 to upregulate the protumorigenic protein NGAL in primary human macrophages. Reporter assays of full-length or deletion constructs of the NGAL promoter provided evidence that NGAL production is STAT3 dependent, activated downstream of the IL-10-Janus kinase (Jak) axis, as well as being C/EBPβ dependent. The involvement of STAT3 and C/EBPβ was shown by chromatin immunoprecipitation (ChIP) and ChIP-Western analysis, as well as decoy oligonucleotides scavenging both STAT3 and C/EBPβ in human macrophages. Furthermore, the production of NGAL in macrophages in response to IL-10 induces cellular growth and proliferation of MCF-7 breast cancer cells. We conclude that both STAT3 and C/EBPβ are needed to elicit IL-10-mediated NGAL expression in primary human macrophages. Macrophage-secreted NGAL shapes the protumorigenic macrophage phenotype to promote growth of MCF-7 breast cancer cells. Our data point to a macrophage-dependent IL-10-STAT3-NGAL axis that might contribute to tumor progression.     

The glomerular mesangial cell: an expanding role for a specialized pericyte

The mesangial cell occupies a central position in the renal glomerulus. It has characteristics of a modified smooth muscle cell, but is also capable of a number of other functions. Among these are generation of prostaglandins (PGs) and mediators of inflammation; production and breakdown of basement membrane and other biomatrix material; synthesis of cytokines; and uptake of macromolecules, including immune complexes. In terms of its smooth muscle activity, the mesangial cell contracts or relaxes in response to a number of vasoactive agents. This ability allows the cells to modify glomerular filtration locally. The cellular mechanism of action of many agents influencing mesangial cells involves activation of phospholipase C for phosphatidylinositol 4,5-bisphosphate. This results in generation of inositol trisphosphate and release of intracellular calcium. Mesangial cell relaxation can be mediated by enhanced cAMP or cGMP generation. Many vasoactive substances also stimulate PG production by mesangial cells. This involves activation of both phospholipase C and A2, the latter being responsible for the release of arachidonic acid. Mesangial cells are also capable of endocytosis of macromolecules, including immune complexes. This is initiated by binding to a specific receptor, resulting in formation of PG, platelet-activating factor, and reactive oxygen species. Mesangial cells can generate interleukin 1 and platelet-derived growth factor and respond to these in an autocrine manner. Thus, the mesangial cell not only can control glomerular filtration, but may also be involved in the response to local injury, including cell proliferation and basement membrane remodeling.