Unconventional T cells and kidney disease

Unconventional T cells are a diverse and underappreciated group of relatively rare lymphocytes that are distinct from conventional CD4⁺ and CD8⁺ T cells, and that mainly recognize antigens in the absence of classical restriction through the major histocompatibility complex (MHC). These non-MHC-restricted T cells include mucosal-associated invariant T (MAIT) cells, natural killer T (NKT) cells, γδ T cells and other, often poorly defined, subsets. Depending on the physiological context, unconventional T cells may assume either protective or pathogenic roles in a range of inflammatory and autoimmune responses in the kidney. Accordingly, experimental models and clinical studies have revealed that certain unconventional T cells are potential therapeutic targets, as well as prognostic and diagnostic biomarkers. The responsiveness of human Vγ9Vδ2 T cells and MAIT cells to many microbial pathogens, for example, has implications for early diagnosis, risk stratification and targeted treatment of peritoneal dialysis-related peritonitis. The expansion of non-Vγ9Vδ2 γδ T cells during cytomegalovirus infection and their contribution to viral clearance suggest that these cells can be harnessed for immune monitoring and adoptive immunotherapy in kidney transplant recipients. In addition, populations of NKT, MAIT or γδ T cells are involved in the immunopathology of IgA nephropathy and in models of glomerulonephritis, ischaemia-reperfusion injury and kidney transplantation.

Changes in the Peritoneal Interstitium and Their Effect on Peritoneal Transport

Transperitoneal transport is a complicated process that includes diffusion and convection across the walls of blood microvessels into tissue interstitium, transport through the interstitium, and final passage across the peritoneum to the dialysis solution in the cavity. The purpose of this paper is to briefly review the normal physiology of this process and then to summarize the events that occur in response to inflammation within the cavity. These events begin with stimulation of macrophages, which in turn secrete cytokines. The cytokines stimulate mesothelial cells and fibroblasts in the tissue to synthesize and secrete other mediators. Those mediators initiate the complex events through which leukocytes migrate from blood vessel lumens through the interstitium and into the cavity. Much of the available data is from model in vitro systems, and therefore in vivo events must be deduced or hypothesized.

Dendritic Cells as Arbiters of Peritoneal Immune Responses

During the past few years, there has been a substantial increase in the understanding of innate immunity. Dendritic cells are emerging as key players in the orchestration of this early phase of immune responses, with a role that will translate into the subsequent type of adaptive immune response against infection. Here we provide an overview of dendritic cell differentiation and function, with particular emphasis on those features unique to the immune defense of the peritoneal cavity and in the context of peritoneal dialysis-associated immune responses. The reader is referred to the primary references included in the accompanying list for specific details in this fascinating field.

Neutrophil-derived miR-223 as local biomarker of bacterial peritonitis

Infection remains a major cause of morbidity, mortality and technique failure in patients with end stage kidney failure who receive peritoneal dialysis (PD). Recent research suggests that the early inflammatory response at the site of infection carries diagnostically relevant information, suggesting that organ and pathogen-specific "immune fingerprints" may guide targeted treatment decisions and allow patient stratification and risk prediction at the point of care. Here, we recorded microRNA profiles in the PD effluent of patients presenting with symptoms of acute peritonitis and show that elevated peritoneal miR-223 and reduced miR-31 levels were useful predictors of bacterial infection. Cell culture experiments indicated that miR-223 was predominantly produced by infiltrating immune cells (neutrophils, monocytes), while miR-31 was mainly derived from the local tissue (mesothelial cells, fibroblasts). miR-223 was found to be functionally stabilised in PD effluent from peritonitis patients, with a proportion likely to be incorporated into neutrophil-derived exosomes. Our study demonstrates that microRNAs are useful biomarkers of bacterial infection in PD-related peritonitis and have the potential to contribute to disease-specific immune fingerprints. Exosome-encapsulated microRNAs may have a functional role in intercellular communication between immune cells responding to the infection and the local tissue, to help clear the infection, resolve the inflammation and restore homeostasis.

The local inflammatory responses to infection of the peritoneal cavity in humans: their regulation by cytokines, macrophages, and other leukocytes

Studies on infection-induced inflammatory reactions in humans rely largely on findings in the blood compartment. Peritoneal leukocytes from patients treated with peritoneal dialysis offer a unique opportunity to study in humans the inflammatory responses taking place at the site of infection. Compared with peritoneal macrophages (pMϕ) from uninfected patients, pMϕ from infected patients display ex vivo an upregulation and downregulation of proinflammatory and anti-inflammatory mediators, respectively. Pro-IL-1β processing and secretion rather than synthesis proves to be increased in pMϕ from infectious peritonitis suggesting up-regulation of caspase-1 in vivo. A crosstalk between pMϕ, γδ T cells, and neutrophils has been found to be involved in augmented TNFα expression and production during infection. The recent finding in experimental studies that alternatively activated macrophages (Mϕ2) increase by proliferation rather than recruitment may have significant implications for the understanding and treatment of chronic inflammatory conditions such as encapsulating peritoneal sclerosis (EPS).

Human peritoneal fibroblasts are a potent source of neutrophil-targeting cytokines: a key role of IL-1beta stimulation

Polymorphonuclear leukocyte (PMN) infiltration is a cardinal feature of peritonitis. CXC chemokine ligands 1 and 8 (CXCL1 and CXCL8), and the cytokine granulocyte colony-stimulating factor (G-CSF) are the key mediators of PMN accumulation. Increasing evidence points to an important role of human peritoneal fibroblasts (HPFB) in the response of the peritoneum to infection. We have examined the synthesis of PMN-targeting cytokines by HPFB exposed to intraperitoneal milieu as represented by peritoneal dialysate effluent (PDE) from patients undergoing peritoneal dialysis. PDE obtained during peritonitis, but not during infection-free periods, significantly increased production of CXCL1, CXCL8, and G-CSF by HPFB. The effect was largely blocked by antibodies to interleukin-1beta (IL-1beta), whereas neutralization of tumor necrosis factor-alpha (TNFalpha) had no major effect. Similar pattern of inhibition was observed when HPFB were exposed to conditioned media from endotoxin-stimulated peritoneal macrophages. Significance of IL-1beta stimulation was further shown in experiments with recombinant cytokines. Compared with TNFalpha, exposure of HPFB to recombinant IL-1beta resulted in a much higher release of PMN-targeting cytokines. The assessment of mRNA degradation revealed that the IL-1beta-induced transcripts of CXCL1, CXCL8, and G-CSF were more stable compared with those induced by TNFalpha. These data indicate that HPFB can be a significant source of PMN-targeting cytokines when stimulated with IL-1beta in the inflamed peritoneum.

Intrinsic Cells: Mesothelial Cells — Central Players in Regulating Inflammation and Resolution

Background

Preservation of the structural and functional integrity of the peritoneum is essential to maintain the dialytic efficacy of the peritoneal membrane. Although much improvement has been made to peritoneal dialysis (PD) fluids, they remain bioincompatible, and together with peritonitis, they continue to induce peritoneal inflammation and fibrosis.

Method

This article reviews the putative factors that mediate mesothelial cell inflammation during PD, and the mechanisms by which mesothelial cells attempt to regulate and resolve peritoneal inflammation.

Results

The mesothelium is the first line of defense to foreign particles and chemicals in the peritoneal cavity. Constant exposure of the mesothelium to the bioincompatible constituents of PD solutions results in denudation of the mesothelium and loss of the peritoneal cavity's protective layer. Detached mesothelial cells in PD solutions have the capacity to replenish the mesothelial layer through their ability to migrate and attach to areas of denudation. Mesothelial cells synthesize a plethora of growth factors, matrix proteins, and proteoglycans that aid in the reparative process and regulate the formation of chemotactic gradients that are essential for infiltration of leukocytes to sites of injury.

Conclusions

Far from being bystanders in peritoneal function, mesothelial cells have been shown to play a dynamic role in peritoneal homeostasis and immunoregulation. Studies have highlighted the potential use of mesothelial cells in gene therapy and cell transplantation, both of which may provide novel therapeutic strategies for the preservation of the peritoneum during PD.

Nod1/RICK and TLR signaling regulate chemokine and antimicrobial innate immune responses in mesothelial cells

Mesothelial cells that line the serous cavities and outer surface of internal organs are involved in inflammatory responses induced by microbial stimuli and bacterial infection. Upon exposure to bacterial products, mesothelial cells secrete chemokines, but the signaling pathways by which these cells recognize bacteria to mediate innate immune responses remain largely unknown. We report that stimulation of primary peritoneal mesothelial cells via nucleotide-binding oligomerization domain (Nod)1, a member of the intracytoplasmic Nod-like receptor family, induced potent secretion of the chemokines CXCL1 and CCL2 as well as expression of inducible NO synthase and such responses required the kinase RICK. Mesothelial cells also produced chemokines in response to TLR2, TLR3, TLR4, and TLR5 agonists, but unlike that induced by Nod1 stimulation, the TLR-mediated responses were independent of RICK. Yet, Nod1 stimulation of mesothelial cells via RICK enhanced chemokine secretion induced by LPS or IFN-gamma and cooperated with IFN-gamma in the production of NO. The i.p. administration of KF1B, a synthetic Nod1 agonist, elicited chemokine production in the serum and peritoneal fluid as well as the recruitment of neutrophils into the peritoneal cavity of wild-type mice, but not RICK-deficient mice. Finally, infection of mesothelial cells with Listeria monocytogenes induced production of CXCL1 and this response was significantly reduced in Nod1- or RICK-deficient cells. These results define mesothelial cells as microbial sensors through TLRs and Nod-like receptors and identify Nod1 and RICK as important mediators of chemokine and antimicrobial responses in mesothelial cells.

Characterization of human peritoneal dendritic cell precursors and their involvement in peritonitis

Scattered evidence suggests that the human peritoneal cavity contains cells of the dendritic cell (DC) lineage but their characterization is missing. Here, we report that the peritoneal cavity of normal subjects and of stable patients on peritoneal dialysis (PD) contains a population of CD14(+) cells that can differentiate into DCs or macrophages. Within this pool, we characterized a CD14(+)CD4(+) cell subset (2.2% of the peritoneal cells) fulfilling the definition of myeloid DC precursors or pre-DC1 cells. These cells expressed high levels of HLA-DR, CD13, CD33, and CD86, and low levels of CD40, CD80, CD83, CD123, CD209, TLR-2 and TLR-4. These cells retained CD14 expression until late stages of differentiation, despite concomitant up-regulation of DC-SIGN (CD209), CD1a, CD80 and CD40. Peritoneal pre-DC1 cells had endocytic capacity that was down-regulated upon LPS/IFN-gamma stimulation, were more potent allo-stimulators than peritoneal CD14(+)CD4(-/lo) cells and monocyte-derived macrophages, and induced Th1 cytokine responses. More importantly, the number of peritoneal pre-DC1 cells increased during PD-associated peritonitis, with a different profile for Gram positive and Gram negative peritonitis, suggesting that these cells participate in the induction of peritoneal adaptive immune responses, and may be responsible for the bias towards Th1 responses during peritonitis.

The transport barrier in intraperitoneal therapy

The peritoneal cavity is important in clinical medicine because of its use as a portal of entry for drugs utilized in regional chemotherapy and as a means of dialysis for anephric patients. The barrier between the therapeutic solution in the cavity and the plasma does not correspond to the classic semipermeable membrane but instead is a complex structure of cells, extracellular matrix, and blood microvessels in the surrounding tissue. New research on the nature of the capillary barrier and on the orderly array of extracellular matrix molecules has provided insights into the physiological basis of osmosis and the alterations in transport that result from infusion of large volumes of fluid. The anatomic peritoneum is highly permeable to water, small solutes, and proteins and therefore is not a physical barrier. However, the cells of the mesothelium play an essential role in the immune response in the cavity and produce cytokines and chemokines in response to contact with noncompatible solutions. The process of inflammation, which depends on the interaction of mesothelial, interstitial, and endothelial cells, ultimately leads to angiogenesis and fibrosis and the functional alteration of the barrier. New animal models, such as the transgenic mouse, will accelerate the discovery of methods to preserve the functional peritoneal barrier.

Children with chronic renal failure have reduced numbers of memory B cells

Reduced serum IgG and subclass levels have been demonstrated in children with chronic renal failure. To study possible causes of this reduction, we analysed B cell subset composition, T helper cell frequencies and immunoglobulin (Ig) production capacity in vitro in children with chronic renal failure, with or without dialysis treatment. B cell subsets were characterized by determining CD27, IgM, IgD and CD5 expression within the CD19(+) population. Intracellular expression of interferon (IFN)-gamma, interleukin (IL)-2 and IL-4 in PMA/ionomycin-stimulated peripheral blood mononuclear cells (PBMC) was used to evaluate T helper frequencies. The capacity of B cells to secrete Ig in vitro was determined by measuring IgG(1), IgG(2) and IgM in culture supernatants of anti-CD2/CD28 monoclonal antibody (MoAb)- or SAC/IL-2-stimulated PBMC. Memory B cell numbers (identified as percentage or absolute number of CD19(+) IgM-IgD- or CD19(+)CD27(+) lymphocytes) were lower in children treated with haemodialysis (HD), peritoneal dialysis (PD) and children with chronic renal failure before starting dialysis treatment (CRF) compared to healthy controls (HC) (P < 0.05). Compared with HC, CD5(+) (naive) B cells were reduced in HD-treated patients but not for PD or for children with chronic renal failure before starting dialysis treatment (CRF). No significant differences in CD4(+) T helper cell subsets were found between the groups. However, CRF children had a higher percentage of IFN-gamma producing CD8(+) T lymphocytes compared to HC (P = 0.02). Finally, IgG(1), IgG(2) and IgM production in vitro was similar in the four groups. In conclusion, significantly lower numbers of memory type B cells were found in children with chronic renal failure compared to healthy controls. This reduction may contribute to the low Ig levels found in these children.

Dialysate Leukocytes, sICAM-1, Hyaluronan and IL-6: Predictors of Outcome of Peritonitis?

BACKGROUND/AIMS

Despite effective antibiotic therapy, peritonitis still remains a major problem in peritoneal dialysis (PD). The aim of the present study was to investigate changes of CRP, dialysate leukocytes and IL-6, hyaluronan (HA) and sICAM-1 in dialysate during and after peritonitis and their association to the outcome of peritonitis.

METHODS

Dialysate IL-6, HA and sICAM-1 were measured at the onset and on day 4, at the end of the treatment and 2 months after onset of peritonitis. Furthermore, CRP and dialysate leukocytes were measured on days 1-4.

RESULTS

All measured soluble factors were higher on the first and fourth day than at the end of the treatment. sICAM-1 and HA were lower at the end of the treatment in patients who later had a relapse/re-infection. IL-6 remained higher 2 months after clinically cured peritonitis. CRP and dialysate leukocytes were higher on day 4 in patients with poor outcome.

CONCLUSIONS

Peritonitis causes increased excretion of soluble factors. Low concentrations of sICAM-1 and HA at the end of the treatment were negative prognostic indicators. Higher IL-6 levels after peritonitis could be a sign of ongoing inflammation in the peritoneal membrane. Delayed decrease in CRP and dialysate leukocytes may indicate poor outcome.

In vitro and in vivo models for peritonitis demonstrate unchanged neutrophil migration after exposure to dialysis fluids

BACKGROUND

Recurrent infections in peritoneal dialysis (PD) patients may alter the abdominal wall resulting in an impairment of its dialysis capacity. In this study we investigated both in vitro and in vivo the effects of mesothelial exposure to dialysis fluids on the migration of neutrophils and their capacity to clear a bacterial infection.

METHODS

First, we evaluated neutrophil migration in an in vitro transwell model for the peritoneal membrane with monolayers of primary human mesothelial cells (MC) on the lower side and primary human endothelial cells (EC) on top of the same transwell membrane, upon exposure of MC to PD fluid (PDF)-derived components. In addition to this in vitro model, we combined chronic peritoneal exposure to PDF with a peritoneal infection model in the rat. We investigated the kinetics of the chemokine response, neutrophil recruitment and bacterial clearance.

RESULTS

Known chemoattractants, such as fMLP and IL-8, strongly increased neutrophil migration across both cell layers in the in vitro model of the peritoneal membrane. Pre-incubation of the MC layer for 48 h with 55 mM glucose, a combination of two glucose degradation products, methylglyoxal and 3-deoxyglucosone, or conventional dialysis fluid (1:4 dilution), however, did not change the IL-8-induced migration of neutrophils. In concert with this finding we demonstrated an unchanged MC expression of ICAM-1 and VCAM-1 after these pre-treatments. Unexpectedly, chronic i.p. exposure to conventional PDF or a recently developed lactate/bicarbonate-buffered PDF in a rat peritoneal exposure model strongly hampered the chemokine response upon bacterial challenge. Nevertheless, neutrophil recruitment and bacterial clearance were effective and did not differ from rats not pre-exposed to PDF.

CONCLUSIONS

We conclude that exposure of MC to PDF does not hamper the recruitment of functional neutrophils upon challenge.

Major involvement of CD40 in the regulation of chemokine secretion from human peritoneal mesothelial cells

BACKGROUND

CD40 is a member of the tumor necrosis factor (TNF) family of receptors, whose ligand, CD154, is expressed by activated mononuclear cells. CD40 activation is a major immune regulatory pathway and is important for the regulation of chemokine and cytokine secretion. This study investigates the effect of CD40 ligation on the secretion of chemokines from human peritoneal mesothelial cells (HPMC).

METHODS

We activated CD40 in HPMC along with combinations of TNF-alpha, interleukin-1 (IL-1), and interferon gamma (IFN-gamma), and evaluated the mRNA levels and protein secretion of regulated upon activation, normal T-cell expressed and secreted (RANTES), monocyte chemoattractant protein-1 (MCP-1), and IL-8.

RESULTS

CD40 ligation had a small stimulatory effect on the secretion of all three chemokines, while TNF-alpha, IL-1 and IFN-gamma induced their secretion in a dose-dependent manner. The combination of CD40 ligation with either IL-1 or TNF-alpha increased chemokine secretion additively. IFN-gamma and CD40 ligation acted in synergy to induce the secretion of the mononuclear recruiting chemokines RANTES and MCP-1 (up to approximately 36-fold and approximately threefold, respectively), for which the combination of all three cytokines with CD40 ligation was extremely potent. In contrast, the secretion of the neutrophil chemoattractant IL-8, induced by CD40 ligation or by the combination of IL-1 and TNF-alpha, was reduced in the presence of IFN-gamma.

CONCLUSION

In light of our data, it is reasonable to suggest that in the mononuclear phase of peritonitis, IFN-gamma and CD154, expressed by activated mononuclear cells, diminish IL-8 secretion from HPMC and thus inhibit neutrophil recruitment. At the same time, the two act in synergy to induce the secretion of RANTES and MCP-1 from HPMC. Hence, by regulating chemokine secretion, CD40 may be involved in peritonitis and in the development of late phase mononuclear predominance.

Differential regulation of chemokine production in human peritoneal mesothelial cells: IFN-gamma controls neutrophil migration across the mesothelium in vitro and in vivo

Leukocyte recruitment into the infected peritoneal cavity consists of an early, predominant polymorphonuclear leukocyte (PMN) influx and subsequent, prolonged mononuclear cell migration phase. Although chemokine secretion by resident peritoneal cells plays a primary role in mediating this migration, the mechanisms involved in controlling the switch in phenotype of cell infiltrate remain unclear. The present study investigates a potential role for the Th1-type cytokine IFN-gamma in the process of leukocyte recruitment into the peritoneal cavity. Stimulation of cultured human peritoneal mesothelial cells with IFN-gamma (1-100 U/ml) alone or in combination with IL-1beta (100 pg/ml) or TNF-alpha (1000 pg/ml) resulted in significant up-regulation of monocyte chemoattractant protein-1 and RANTES protein secretion. In contrast, IFN-gamma inhibited basal and IL-1beta-, and TNF-alpha-induced production of IL-8. The modulating effects of IFN-gamma on chemokine production occurred at the level of gene expression, and the degree of regulation observed was dependent on the doses of IL-1beta and TNF-alpha used. Analysis of the functional effects of IFN-gamma on IL-1beta-induced transmesothelial PMN migration with an in vitro human transmigration system and an in vivo murine model of peritoneal inflammation demonstrated that IFN-gamma was able to down-regulate PMN migration induced by optimal doses of IL-1beta. These effects were mediated in vivo via down-regulation of CXC chemokine synthesis. These findings suggest that IFN-gamma may play a role in controlling the phenotype of infiltrating leukocyte during the course of an inflammatory response, in part via regulation of resident cell chemokine synthesis.

Synthesis of C-X-C and C-C chemokines by human peritoneal fibroblasts: induction by macrophage-derived cytokines

Leukocyte accumulation during peritonitis is believed to be controlled by chemotactic factors released by resident peritoneal macrophages or mesothelial cells. Recent data indicate, however, that in many tissues fibroblasts play a key role in mediating leukocyte recruitment. We have therefore examined human peritoneal fibroblasts (HPFBs) for the expression and regulation of C-X-C and C-C chemokines. Quiescent HPFBs secreted monocyte chemoattractant protein (MCP)-1 and interleukin (IL)-8 constitutively. This release could be dose-dependently augmented with the pro-inflammatory cytokines IL-1beta and tumor necrosis factor-alpha. Stimulated IL-8 production reached a plateau within 48 hours while MCP-1 continued to accumulate throughout 96 hours. Induction of IL-8 and MCP-1 synthesis by HPFBs was also triggered by peritoneal macrophage-conditioned medium. This effect was partly related to the presence of IL-1beta as demonstrated by IL-1 receptor antagonist inhibition. Pretreatment of HPFBs with actinomycin D or puromycin dose-dependently reduced cytokine-stimulated IL-8 and MCP-1 secretion, which suggested de novo chemokine synthesis. Indeed, exposure of HPFBs to IL-1beta and tumor necrosis factor-alpha produced a significant up-regulation of IL-8 and MCP-1 mRNA. This effect was associated with the rapid induction of nuclear factor-kappaB binding activity mediated through p65 and p50 subunits, and with a transient increase in the mRNA expression for RelB and inhibitory protein kappaB-alpha proteins. These data indicate that peritoneal fibroblasts are capable of generating large quantities of chemokines under a tight control of nuclear factor-kappaB/Rel transcription factors. Thus, peritoneal fibroblast-derived chemokines may contribute to the intraperitoneal recruitment of leukocytes during peritonitis.

Changes of cytokine profiles during peritonitis in patients on continuous ambulatory peritoneal dialysis

Continuous ambulatory peritoneal dialysis (CAPD) has emerged as an important dialysis treatment modality worldwide. One of the major complications is bacterial peritonitis, which may result in subsequent technique failure because of loss of peritoneal clearance or peritoneal fibrosis. Bacterial peritonitis leads to the release of proinflammatory cytokines from resident and infiltrating cells in the peritoneal cavity. We studied 35 patients undergoing CAPD with acute bacterial peritonitis. All patients treated with antibiotics for 2 weeks after the clinical diagnosis of peritonitis had a good recovery. Peritoneal dialysate effluent (PDE) was collected on days 1, 3, 5, 10, 21, and 42 after the start of treatment. Cell populations were monitored by flow cytometry. PDE levels of interleukin-1beta (IL-1), IL-6, transforming growth factor-beta (TGF-beta), and basic fibroblast growth factor (FGF) were measured by enzyme-linked immunosorbent assay. Gene transcription of TGF-beta in macrophages from PDE was measured by quantitative polymerase chain reaction. Bacterial peritonitis was associated with a sharp increase in total cell and neutrophil counts (400-fold) in PDE up to 3 weeks after peritonitis despite clinical remission (P < 0.0001). There was an increased absolute number of macrophages during the first 3 weeks despite the reduced percentage of macrophages among total cells in PDE compared with noninfective PDE. There was a progressive increase in the percentage of mesothelial cells or dead cells in the total cell population in PDE over the entire 6-week period. PDE levels of IL-1, IL-6, TGF-beta, and FGF increased markedly on day 1 before their levels decreased gradually. PDE levels of these cytokines or growth factors were significantly greater than those in noninfective PDE (n = 76) throughout the study period (P < 0.01). Similarly, TGF-beta complementary DNA (cDNA) molecules per macrophage were significantly greater than those of macrophages in noninfective PDE throughout this period (P < 0.01). There was no significant correlation between PDE levels of TGF-beta and TGF-beta cDNA molecules per macrophage, suggesting that peritoneal macrophages are not the only source of TGF-beta in PDE. We conclude there is an active release of proinflammatory cytokines and sclerogenic growth factors through at least 6 weeks despite apparent clinical remission of peritonitis. The peritoneal cytokine networks after peritonitis may potentially affect the physiological properties of the peritoneal membrane.

Neutrophil migration induced by staphylococcal enterotoxin type A in mice: a pharmacological analysis

Staphylococcal enterotoxin type A induced marked neutrophil migration into the mouse peritoneal cavity and was dependent on the number of resident macrophages. This migratory response was dose- (16-64 microg of staphylococcal enterotoxin type A/cavity) and time-dependent, peaking at 12 h and disappearing after 72 h. Dexamethasone (0.5 mg/kg) inhibited the neutrophil migration induced by staphylococcal enterotoxin type A (32 microg; 42% inhibition). A similar response was observed with the platelet-activating factor-acether receptor antagonist, BN 52021 (ginkgolide B, 3-(1,1-dimethylethyl)-hexahydro-1,4-7b-trihydroxy-8-methyl-9H-1,7alph a (epoxymethano-1H,6alphaH-cyclopenta (c) furo (2,3-b) furo (3', 2': 3,4) cyclopenta (1,2-d) furan-5, 9, 12 (4H)-trione); 10 mg/kg; 57% inhibition), the histamine H2 receptor antagonist, cimetidine (2 mg/kg; 31% inhibition), the lipoxygenase inhibitor, BWA4C (N-(3-phenoxycinnamyl) acetohydroxamic acid); 10 mg/kg; 73% inhibition), and capsaicin (trans-8-methyl-N-vanillyl-6-nonamide), a sensory C-fiber neuropeptide depletor. In contrast, indomethacin (5 mg/kg) had no effect on staphylococcal enterotoxin type A-induced chemotaxis. We conclude that the peritonitis induced by staphylococcal enterotoxin type A in mice is macrophage-dependent. The mechanism whereby staphylococcal enterotoxin type A stimulates macrophages to induce neutrophil recruitment remains to be elucidated.

Leukocyte migration across human peritoneal mesothelial cells is dependent on directed chemokine secretion and ICAM-1 expression

BACKGROUND

Leukocyte migration into the peritoneal cavity is a diagnostic feature of peritonitis in patients treated with peritoneal dialysis (PD). While neutrophil (PMN) influx is characteristic of the acute phase of peritoneal infection, significant mononuclear cell (MNC) infiltration, occurs throughout the whole period of infection. Recent data suggests that human peritoneal mesothelial cell (HPMC) adhesion molecule expression and the synthesis of chemotactic cytokines may be important in the process.

METHODS

In the present study we have examined, the regulation and directed secretion of chemokines (IL-8, MCP-1 and RANTES) and the basolateral to apical migration of unstimulated leukocytes across mesothelial cell monolayers using an in vitro model where HPMC were grown on the porous membrane of tissue culture inserts. Separate experiments have defined the importance of chemokine synthesis and ICAM-1 expression in the transmigration process.

RESULTS

Apical stimulation of HPMC with IL-1 beta or TNF alpha resulted in a time and dose dependent up-regulation of IL-8, MCP-1 and RANTES mRNA expression and synthesis. This secretion was predominately into the apical compartment (> 85%) with all chemokines. Apical pre-stimulation of HPMC resulted in a dose- and time-dependent migration of both PMN and MNC across HPMC. Neutrophil migration was significantly reduced in the presence of appropriate concentrations of polyclonal IL-8 antibody (IL-1 beta (100 pg/ml) 153 +/- 12 versus anti-IL-8 (100 ng/ml) 71 +/- 7 (X 10(3)) PMN, N = 6, P < 0.02) and in the presence of anti-ICAM-1 F(ab)'2 fragments or soluble ICAM-1. Constitutive and cytokine stimulated mononuclear cell migration was significantly reduced in the simultaneous presence of polyclonal MCP-1 or RANTES antibody.

CONCLUSIONS

These data demonstrate that HPMC synthesize IL-8, MCP-1 and RANTES in response to inflammatory cytokines. HPMC-derived C-x-C and C-C chemokines might contribute to the intra-peritoneal recruitment of leukocytes during peritoneal inflammation.

Chemokines produced by mesothelial cells: huGRO-alpha, IP-10, MCP-1 and RANTES

Recently we showed the in vivo relevance of chemokines in cases of bacterial peritonitis in continuous ambulatory peritoneal dialysis (CAPD) patients. Mesothelial cells, the most numerous cells in the peritoneal cavity, are hypothesized to function as a main source of chemokine production. We investigated the time- and dose-dependent expression patterns of four chemokines by mesothelial cells at the mRNA and protein level in response to stimulation with physiological doses of proinflammatory mediators that are present at the site of bacterial inflammation. Besides the chemokines huGRO-alpha (attractant for neutrophils), MCP-1 and RANTES (monocyte attractants), the expression and production of IP-10 was analysed. Mesothelial cells were cultured and stimulated with either IL-1beta, tumour necrosis factor-alpha (TNF-alpha) or IFN-gamma or combinations of these. The time- and dose-dependent mRNA expression of the chemokines was determined by Northern blot analysis and the protein production by ELISA. It was concluded that mesothelial cells could indeed be triggered by the mentioned stimuli to induce mRNA and protein production (huGRO-alpha and IP-10) or to augment constitutive protein production (MCP-1). However, RANTES mRNA and protein production could only be induced in some cases and only in small amounts. The chemokine response of mesothelial cells was regulated differentially, depending on the stimulus and the chemokine measured. In distinct cases, combination of the stimuli led to synergy in mRNA expression and protein production. The presented in vitro data support our hypothesis that mesothelial cells in vivo are the main source of relevant chemokines in response to proinflammatory mediators, suggesting an important role for mesothelial cells in host defence.