Peritoneal cell labelling: a study on the migration of macrophages and dendritic cells towards the gut

T Lymphocytes: The “Cellular” Arm of Acquired Immunity in the Peritoneum

T cells are an important part of the acquired immune response and target specific antigen with their T cell receptor. The peritoneum is a special milieu within which T cells react. We describe briefly the anatomy important for T cell function. T cell biology including antigen presentation, T cell activation, and the different T cell subpopulations are reviewed. We also define innate and acquired immunity and describe the role of polymorphonuclear cells and peritoneal mesothelial cells in the regulation of leukocyte population recruitment during peritonitis. We focus particularly on peritoneal lymphocytes and compare them to the regular lymphocyte populations in the circulation. We illustrate the role of PMCs in antigen presentation and discuss the changes of CD4+ helper T cell subtypes (Th1 and Th2) during peritoneal dialysis. The role of CD8+ cytotoxic T lymphocytes and their possible destructive role for the peritoneal membrane modified by advanced glycation end products are discussed. Polymorphonuclear cells play an important role in the regulation of inflammation and immunity. We describe their possible role in supporting T cells and particularly for generating memory CD8+ T cells by secretion of interleukin-15, a potent T cell growth factor. Light is shed on γδ T cells, a special T cell population that is able to recognize antigens without the restriction of antigen presentation. We end our review with a description of regulatory T cells. This cell population is extremely important in preventing autoimmunity and in the regulation of acquired immunity.

Polypotency of the immunomodulatory effect of pectins

Pectins are the major component of plant cell walls, and they display diverse biological activities including immunomodulation. The pectin macromolecule contains fragments of linear and branched regions of polysaccharides such as homogalacturonan, rhamnogalacturonan-I, xylogalacturonan, and apiogalacturonan. These structural features determine the effect of pectins on the immune system. The backbones of pectic macromolecules have immunosuppressive activity. Pectins containing greater than 80% galacturonic acid residues were found to decrease macrophage activity and inhibit the delayed-type hypersensitivity reaction. Branched galacturonan fragments result in a biphasic immunomodulatory action. The branched region of pectins mediates both increased phagocytosis and antibody production. The fine structure of the galactan, arabinan, and apiogalacturonan side chains determines the stimulating interaction between pectin and immune cells. This review summarizes data regarding the relationship between the structure and immunomodulatory activity of pectins isolated from the plants of the European north of Russia and elucidates the concept of polypotency of pectins in native plant cell walls to both stimulate and suppress the immune response. The possible mechanisms of the immunostimulatory and anti-inflammatory effects of pectins are also discussed.

12/15-Lipoxygenase regulates the inflammatory response to bacterial products in vivo

The peritoneal macrophage (Mphi) is the site of greatest 12/15-lipoxygenase (12/15-LOX) expression in the mouse; however, its immunoregulatory role in this tissue has not been explored. Herein, we show that 12/15-LOX is expressed by 95% of resident peritoneal CD11b(high) cells, with the remaining 5% being 12/15-LOX(-). 12/15-LOX(+) cells are phenotypically defined by high F4/80, SR-A, and Siglec1 expression, and enhanced IL-10 and G-CSF generation. In contrast, 12/15-LOX(-) cells are a dendritic cell population. Resident peritoneal Mphi numbers were significantly increased in 12/15-LOX(-/-) mice, suggesting alterations in migratory trafficking or cell differentiation in vivo. In vitro, Mphi from 12/15-LOX(-/-) mice exhibit multiple abnormalities in the regulation of cytokine/growth factor production both basally and after stimulation with Staphylococcus epidermidis cell-free supernatant. Resident adherent cells from 12/15-LOX(-/-) mice generate more IL-1, IL-3, GM-CSF, and IL-17, but less CCL5/RANTES than do cells from wild-type mice, while Staphylococcus epidermidis cell-free supernatant-elicited 12/15-LOX(-/-) adherent cells release less IL-12p40, IL-12p70, and RANTES, but more GM-CSF. This indicates a selective effect of 12/15-LOX on peritoneal cell cytokine production. In acute sterile peritonitis, 12/15-LOX(+) cells and LOX products were cleared, then reappeared during the resolution phase. The peritoneal lavage of 12/15-LOX(-/-) mice showed elevated TGF-beta1, along with increased immigration of monocytes/Mphi, but decreases in several cytokines including RANTES/CCL5, MCP-1/CCL2, G-CSF, IL-12-p40, IL-17, and TNF-alpha. No changes in neutrophil or lymphocyte numbers were seen. In summary, endogenous 12/15-LOX defines the resident MPhi population and regulates both the recruitment of monocytes/Mphi and cytokine response to bacterial products in vivo.

The limitation of IL-10-exposed dendritic cells in the treatment of experimental autoimmune myasthenia gravis and myasthenia gravis

Dendritic cells (DC) are highly specialized antigen presenting cells that play critical roles as instigators and regulators of immune responses including B cell function, antibody synthesis and isotype switch. In this study, we compared immunotherapeutic effect of IL-10-treated DC (IL-10-DC) via both intraperitoneal (i.p.) and subcutaneous (s.c.) delivery in rats with incipient experimental autoimmune myasthenia gravis (EAMG). Spleen DC were isolated from onset of EAMG on day 39 post-immunization, exposed in vitro to IL-10, and then injected into incipient EAMG at dose of 1 x 10(6) cells/rat on day 5 after immunization. Intraperitoneal administration of IL-10-DC suppressed clinical scores, anti-acetylcholine receptors (AChR) antibody secreting cells, antigen-specific IL-10/IFN-gamma production and T cell proliferation compared to control EAMG rats. Importantly, IL-10-DC, if given by s.c. route, failed to ameliorate clinical sign of EAMG. Simultaneously, T cell proliferation, anti-AChR antibody secreting cells and IL-10/IFN-gamma production had no alteration, as compared to control EAMG rats. Both in vitro and in vivo experiments showed that treatment of IL-10 inhibited the migration of DC toward MIP-3beta and lymph node, indicating that in vitro manipulation of DC with IL-10 alters the migration of DC that influences the therapeutic effect in the treatment of autoimmune diseases. In MG patients, neither the improvement of clinical symptom nor the alteration of immunological parameter was observed through s.c. delivery of IL-10-DC, suggesting the limitation of IL-10-DC in the treatment of MG patients.

Peritoneal antigen-presenting cells pulsed in vivo with myelin basic protein induce the suppression of experimental autoimmune encephalomyelitis (EAE) in Wistar rats

Suppression of Experimental Autoimmune Encephalomyelitis (EAE) can be achieved by i.p. administration of soluble myelin basic protein (MBP) in adult Wistar rats before the immunization. In the present work, we analyze the role of peritoneal antigen-presenting cells (APC) in the induction of tolerance to EAE. Peritoneal cells (PC) pulsed in vivo with MBP were obtained from rats that had been intraperitoneally injected 2 h previously with soluble MBP (MBP-PC) and then inoculated in recipient rats before the induction of EAE. Our findings show that the i.p. treatment of the animals with MBP-PC before the immunization was able to diminish the incidence and severity of the disease, reduce the histological alterations, abrogate the proliferative response against MBP and change the pattern of the humoral response to MBP. Moreover, when spleen mononuclear cells (MNC) from tolerant animals were cultured together with spleen MNC from sick animals, a dose-dependent inhibition of the proliferative response was observed, arguing for the presence of a regulatory cell population in the tolerant animals. It is also demonstrated that the MBP-PC are activated and their capability of inducing suppression of EAE is highly associated with the enhanced expression of MHC class II IA molecule. Our results show that peritoneal cells pulsed in vivo with MBP are able to induce tolerance and suggest that the up-regulation of MHC class II on MBP-PC is a necessary event for tolerance induction in our model.

The pathobiology of peritonitis

The peritoneum is more than a mechanical covering that allows for the easy gliding of opposed peritoneal surfaces. The peritoneal mesothelial cells facilitate the action of powerful innate immune mechanisms. In addition, the peritoneal-associated lymphoid tissues contain unique cells that may play a crucial role in the localization of intraperitoneal infection. A clearer understanding of the molecular and cellular events underlying peritoneal functions in both the unstimulated and stimulated state will aid future treatment of peritonitis.

Review: Peyer's patches

The function of Peyer's patches as antigenic sampling sites involves the complex interplay of a variety of mechanisms that aim to recognize luminal antigens, induce an immunological response and decrease the incidence of antigen translocation across the mucosal epithelium. This is achieved by M cells, which facilitate the uptake of luminal antigens, a vascular architecture that promotes the retention of absorbed antigens within the patch interstitium (allowing for maximal antigenic activation of lymphocytes) and the presence of lymphoid follicles that contain antigen-presenting cells and lymphocytes. Lymphocytes encountering antigen in the Peyer's patches proliferate, differentiate into fully mature antigen-specific effector cells and migrate to the mesenteric lymph nodes where they undergo final maturation. The mature lymphocytes then enter the systemic circulation and migrate throughout the other mucosa-associated lymphoid tissues of the body and "home' into the gut via high endothelial venules and gut-associated lymphoid tissue-specific adhesion molecules, providing antigen-specific lymphocytes at sites likely to re-encounter the antigen.

Peritoneal defences and peritoneum-associated lymphoid tissue

The peritoneum is mainly protected by the innate immune system. This consists of mechanical clearance of the peritoneal cavity, activation of complement, and the actions of polymorphonuclear neutrophils and macrophages. The specific immune system, which is mediated by the activity of lymphocytes, provides a secondary amplification system that may be of great importance for patients with intraperitoneal sepsis. This review provides an overview of the relevant innate immune mechanisms and explores the possible role of peritoneum-associated lymphoid tissue.

Origin and steady-state turnover of major histocompatibility complex class II-positive dendritic cells and resident-tissue macrophages in the iris of the rat eye

Recent studies have identified distinct but co-existing networks of resident tissue macrophages and MHC class II-positive DC present in tissues bordering the anterior chamber of the eye, a site classically regarded as 'immune-privileged'. As the DC network, present at approximately 500 cells/mm2, accounts for virtually all MHC class II immunostaining in these tissues and possesses potent capacity to stimulate primary allogenic responses in vitro, it is proposed that these cells may play an important role in immune surveillance of the anterior chamber. Tissue macrophage and DC population kinetics in the iris were examined by using X-irradiation exposure to interrupt the steady-state renewal of these cells by haematopoietically derived precursors. MHC class II-positive iris DC exhibited a half-life of approximately 3 days, a rapid turnover rate which closely resembled that of DC present in mucosal epithelia. In contrast, the resident tissue macrophage population displayed a considerably slower turnover (half-life of 10-12 days) comparable to that of epidermal Langerhans cells in the present study. Bone marrow transplantation studies confirmed the haematopoietic origin of the iris DC population. The present study provides the first estimates of the steady-state population kinetics of antigen-presenting cell populations in the iris and has important implications for understanding the role of these cells in immunological homeostasis of the anterior chamber.