Lymphocytes modulate peritoneal leukocyte recruitment in peritonitis

Chondroitin Sulfate from Oreochromis niloticus Waste Reduces Leukocyte Influx in an Acute Peritonitis Model

Oreochromis niloticus (tilapia) is one of the most cultivated fish species worldwide. Tilapia farming generates organic waste from fish removal processes in nurseries. Visceral waste can damage natural ecosystems. Therefore, the use of this material as a source of biomolecules helps reduce environmental impacts and improve pharmacological studies. Tilapia viscera were subjected to proteolysis and complexation with an ion-exchange resin. The obtained glycosaminoglycans were purified using ion exchange chromatography (DEAE-Sephacel). The electrophoretic profile and analysis of 1H/13C nuclear magnetic resonance (NMR) spectra allowed for the characterization of the compound as chondroitin sulfate and its sulfation position. This chondroitin was named CST. We tested the ability of CST to reduce leukocyte influx in acute peritonitis models induced by sodium thioglycolate and found a significant reduction in leukocyte migration to the peritoneal cavity, similar to the polymorphonuclear population of the three tested doses of CST. This study shows, for the first time, the potential of CST obtained from O. niloticus waste as an anti-inflammatory drug, thereby contributing to the expansion of the study of molecules with pharmacological functions.

Mechanisms of Peritoneal Fibrosis: Focus on Immune Cells-Peritoneal Stroma Interactions

Peritoneal fibrosis is characterized by abnormal production of extracellular matrix proteins leading to progressive thickening of the submesothelial compact zone of the peritoneal membrane. This process may be caused by a number of insults including pathological conditions linked to clinical practice, such as peritoneal dialysis, abdominal surgery, hemoperitoneum, and infectious peritonitis. All these events may cause acute/chronic inflammation and injury to the peritoneal membrane, which undergoes progressive fibrosis, angiogenesis, and vasculopathy. Among the cellular processes implicated in these peritoneal alterations is the generation of myofibroblasts from mesothelial cells and other cellular sources that are central in the induction of fibrosis and in the subsequent functional deterioration of the peritoneal membrane. Myofibroblast generation and activity is actually integrated in a complex network of extracellular signals generated by the various cellular types, including leukocytes, stably residing or recirculating along the peritoneal membrane. Here, the main extracellular factors and the cellular players are described with emphasis on the cross-talk between immune system and cells of the peritoneal stroma. The understanding of cellular and molecular mechanisms underlying fibrosis of the peritoneal membrane has both a basic and a translational relevance, since it may be useful for setup of therapies aimed at counteracting the deterioration as well as restoring the homeostasis of the peritoneal membrane.

Oral administration of nano-emulsion curcumin in mice suppresses inflammatory-induced NFκB signaling and macrophage migration

Despite the widespread use of curcumin for centuries in Eastern medicine as an anti-inflammatory agent, its molecular actions and therapeutic viability have only recently been explored. While curcumin does have potential therapeutic efficacy, both solubility and bioavailability must be improved before it can be more successfully translated to clinical care. We have previously reported a novel formulation of nano-emulsion curcumin (NEC) that achieves significantly greater plasma concentrations in mice after oral administration. Here, we confirm the immunosuppressive effects of NEC in vivo and further examine its molecular mechanisms to better understand therapeutic potential. Using transgenic mice harboring an NFκB-luciferase reporter gene, we demonstrate a novel application of this in vivo inflammatory model to test the efficacy of NEC administration by bioluminescent imaging and show that LPS-induced NFκB activity was suppressed with NEC compared to an equivalent amount of curcumin in aqueous suspension. Administration of NEC by oral gavage resulted in a reduction of blood monocytes, decreased levels of both TLR4 and RAGE expression, and inhibited secretion of MCP-1. Mechanistically, curcumin blocked LPS-induced phosphorylation of the p65 subunit of NFκB and IκBα in murine macrophages. In a mouse model of peritonitis, NEC significantly reduced macrophage recruitment, but not T-cell or B-cell levels. In addition, curcumin treatment of monocyte derived cell lines and primary human macrophages in vitro significantly inhibited cell migration. These data demonstrate that curcumin can suppress inflammation by inhibiting macrophage migration via NFκB and MCP-1 inhibition and establish that NEC is an effective therapeutic formulation to increase the bioavailability of curcumin in order to facilitate this response.

Novel insights into the peritoneal inflammation of rainbow trout (Oncorhynchus mykiss)

The peritoneal cavity has been extensively used as a laboratory model of inflammation in many species, including the teleost fish. Although, the peritoneal cavity of rainbow trout (Oncorhynchus mykiss) was previously shown to contain a resident population of leukocytes, closer information about their exact composition and their functional response to pathogens is still missing. In the presented work, flow cytometric analysis using monoclonal antibodies was performed to characterize this cell population and evaluate its traffic during the first 72 h after antigenic stimulation and infection with Aeromonas salmonicida. Obtained results indicate that the unstimulated peritoneal cavity represents rather a lymphoid niche, dominated by the IgM(+) B cells. Expectedly, the composition changed rapidly after stimulation, which resulted in two complete changes of dominant cell type within first 72 h post injection. While the first stage of inflammation was dominated by myeloid cells, lymphocytes predominated at the later time points, with IgM(+) B cells representing more than two thirds of all cells. Later, the infection experiment elucidated the peritoneal infection and identified the key differences to the antigenic stimulation. Additionally, the data indicate that the resolution of the inflammation depends more on the bacterial clearance by myeloid cells than on regulation by lymphocytes. Taken together, obtained results represent the first complete description of the immune reaction protecting the peritoneal cavity of the fish and shed some light on the conservation of these processes during the evolution.

Regulation of experimental peritonitis: a complex orchestration

Experimental peritonitis is a frequently used inflammatory model to evaluate leukocyte recruitment. By the intrinsic characteristics of the peritoneal cavity, the various resident cell populations have a role to play in the initiation, the modulation and the resolution of peritoneal inflammation. Through various manipulations of these cell populations, we gained important knowledge on their respective roles in peritoneal inflammation. In this brief review, we will focus on the cellular regulation of leukocyte recruitment in experimental peritonitis.

Mast cell-mediated inhibition of abdominal neutrophil inflammation by a PEGylated TLR7 ligand

Although the mechanisms for sustained chemokine gradients and recurring cell infiltration in sterile peritonitis have not been elucidated, toll-like receptors (TLRs) have been implicated. To abate the deleterious recruitment of neutrophils in sterile inflammation, we repeatedly administered a TLR7 ligand that hyposensitized to TLR7 and receptors that converged on the MyD88-signaling intermediary and reduced cellular infiltration in murine autoimmune models of multiple sclerosis and arthritis. To reduce potential adverse effects, a polyethylene glycol polymer was covalently attached to the parent compound (Tolerimod1). The proinflammatory potency of Tolerimod1 was 10-fold less than the unconjugated TLR7 ligand, and Tolerimod1 reduced neutrophil recruitment in chemically induced peritonitis and colitis. The effects of Tolerimod1 were mediated by the radioresistant cells in radiation chimeric mice and by mast cells in reconstituted mast cell-deficient mice (Kit(W-sh)). Although the Tolerimod1 had weak proinflammatory agonist activity, it effectively reduced neutrophil recruitment in sterile peritoneal inflammation.

Sex differences in resident immune cell phenotype underlie more efficient acute inflammatory responses in female mice

Females are protected against mortality arising from severe sepsis; however, the precise mechanisms that confer this survival advantage in females over males are unclear. Resident leukocytes in resting tissues have a significant influence on circulating cytokine levels and recruitment of blood leukocytes during acute inflammatory responses. Whether the phenotype of resident leukocytes is distinct in females is unknown. In the present study, we show that the numbers of leukocytes occupying the naive peritoneal and pleural cavities is higher in female than in male mice and rats, comprising more T and B lymphocytes and macrophages. The altered immune cell composition of the female peritoneum is controlled by elevated tissue chemokine expression. Female resident macrophages also exhibit greater TLR expression and enhanced phagocytosis and NADPH oxidase-mediated bacterial killing. However, macrophage-derived cytokine production is diminished by proportionally more resident immunomodulatory CD4+ T lymphocytes. Ovarian hormones regulate macrophage phenotype, function, and numbers, but have no significant impact on T-lymphocyte populations in females. We have identified a fundamental sex difference in phenotype of resident leukocytes. We propose that the distinct resident leukocyte population in females allows aggressive recognition and elimination of diverse infectious stimuli without recruitment of circulating neutrophils or excessive cytokine production.

Involvement of Interleukin-10 in the Anti-Inflammatory Effect of Sanyinjiao (SP6) Acupuncture in a Mouse Model of Peritonitis

In this study, we determined the anti-inflammatory effect of manual acupuncture at the Sanyinjiao or Spleen 6 (SP6) point on carrageenan-induced peritonitis in mice and investigated mechanisms that may underlie this effect. In the first set of experiments, male Swiss mice were allocated into five groups: the control (sterile saline), dexamethasone (DEXA), invasive sham-acupuncture (non-acupoint), SP6 acupuncture and carrageenan-treated groups. Ten minutes after needle retention or 30 min after DEXA treatment, mice received an intraperitoneal injection of carrageenan (750 μg/mouse). After 4 h, total leukocyte and differential cell counts (neutrophils and mononuclear), myeloperoxidase (MPO) activity, vascular permeability and cytokine levels were evaluated. In another set of experiments, adrenalectomized (ADX) mice were used to study the involvement of the adrenal gland on the therapeutic effects of acupuncture. Mice were allocated into two groups: the ADX and sham-operated animals (Sham ADX) that were subdivided into four subgroups each: the control (sterile saline), DEXA, SP6 acupuncture and carrageenan-treated groups. The SP6 and DEXA treatments inhibited the inflammatory cell infiltration, vascular permeability and MPO activity in carrageenan-injected mice. In addition, the SP6 treatment also increased interleukin (IL)-10 levels. In contrast, when the animals were adrenalectomized, the SP6 treatment failed to reduce total leukocyte and the plasma extravasation. In conclusion, this study clearly demonstrates the anti-inflammatory effect of SP6 acupuncture in a model of carrageenan-induced peritonitis. Our results demonstrated that SP6 acupuncture depends of the adrenal glands and increased IL-10 levels to produce its anti-inflammatory action.

CCR7 regulates lymphocyte egress and recirculation through body cavities

T and B lymphocytes recirculate among blood, lymph, and extralymphoid tissues to ensure immune surveillance and the establishment of self-tolerance. The underlying mechanisms regulating homeostatic lymphocyte recirculation through body cavities are not fully understood. Here, we demonstrate that the homeostatic chemokine receptor CCR7 regulates homeostatic recirculation of lymphocytes through body cavities. CCR7 deficiency results in massive accumulation of CD4(+) and CD8(+) T cells and B-2 B cells in the peritoneal and pleural cavities. The increase in B-2 B and T lymphocytes is not associated with an altered maturation and/or activation status of these cells. Mechanistically, an increase in peritoneal lymphocyte numbers is caused by impaired egress of CCR7-deficient lymphocytes from body cavities. These results establish that CCR7 plays a crucial role in lymphocyte exit from the PerC.