Mast cells in the front line. Innate immunity

Mast cell-sensory neuron crosstalk in allergic diseases

Mast cells (MCs) are tissue-resident immune cells, well-positioned at the host-environment interface for detecting external antigens and playing a critical role in mobilizing innate and adaptive immune responses. Sensory neurons are afferent neurons innervating most areas of the body but especially in the periphery, where they sense external and internal signals and relay information to the brain. The significance of MC-sensory neuron communication is now increasingly becoming recognized, especially because both cell types are in close physical proximity at the host-environment interface and around major organs of the body and produce specific mediators that can activate each other. In this review, we explore the roles of MC-sensory neuron crosstalk in allergic diseases, shedding light on how activated MCs trigger sensory neurons to initiate signaling in pruritus, shock, and potentially abdominal pain in allergy, and how activated sensory neurons regulate MCs in homeostasis and atopic dermatitis associated with contact hypersensitivity and type 2 inflammation. Throughout the review, we also discuss how these 2 sentinel cell types signal each other, potentially resulting in a positive feedback loop that can sustain inflammation. Unraveling the mysteries of MC-sensory neuron crosstalk is likely to unveil their critical roles in various disease conditions and enable the development of new therapeutic approaches to combat these maladies.

The Role of PPAR Alpha in the Modulation of Innate Immunity

Peroxisome proliferator-activated receptor α is a potent regulator of systemic and cellular metabolism and energy homeostasis, but it also suppresses various inflammatory reactions. In this review, we focus on its role in the regulation of innate immunity; in particular, we discuss the PPARα interplay with inflammatory transcription factor signaling, pattern-recognition receptor signaling, and the endocannabinoid system. We also present examples of the PPARα-specific immunomodulatory functions during parasitic, bacterial, and viral infections, as well as approach several issues associated with innate immunity processes, such as the production of reactive nitrogen and oxygen species, phagocytosis, and the effector functions of macrophages, innate lymphoid cells, and mast cells. The described phenomena encourage the application of endogenous and pharmacological PPARα agonists to alleviate the disorders of immunological background and the development of new solutions that engage PPARα activation or suppression.

Inflammatory biomarker, neopterin, enlarges splenic mast-cell-progenitor pool: Prominent impairment of responses in age-related stromal cell-impairment mouse SCI/SAM

Neopterin is produced by monocytes and is a useful biomarker of inflammatory responses. We found that neopterin enhances granulopoiesis, but suppresses B-lymphopoiesis triggered by the positive and negative regulations of cytokines produced by stromal cells in mice. In this study, neopterin was found to regulate mast cell development, which was confirmed in the mouse model of senescent stromal-cell impairment (SCI). In non-SCI mice (=less senescent stage of SCI mice), neopterin decreased the number of colonies of IL-3-dependent mast-cell progenitor cells (CFU-mast) from unfractionated bone-marrow cells, but not that from the lineage-negative bone-marrow cell population without stromal cells in a semisolid in vitro system. Neopterin increased the gene expression and protein production of TGF-beta, a negative regulator of CFU-mast, in cultured stromal cells, indicating that neopterin suppressed CFU-mast colony formation by inducing TGF-beta in stromal cells. In contrast to this in vitro study, in vivo treatment with neopterin did not significantly up-regulate TGF-beta. The intravenous injection of neopterin into mice decreased the number of femoral CFU-mast and the expression level of the gene for stem cell factor (SCF), a positive regulator of CFU-mast, whereas the number of splenic CFU-mast and SCF gene expression level increased. In SCI mice, the in vivo and in vitro responses of mast cell development and cytokine gene expression level to neopterin treatment were less marked than those in non-SCI mice. These results suggest that, firstly, neopterin augments the splenic pool of CFU-mast by the production of SCF, and secondly, such neopterin function becomes impaired during senescence because of an impaired stromal-cell function, resulting in the down-modulation of host-defense mechanisms.

Bacterial infection in cirrhosis impairs coagulation by a heparin effect: a prospective study

BACKGROUND

Bacterial infections have been postulated as a trigger for variceal bleeding in cirrhotic patients, and impair coagulation evaluated by thrombelastography (TEG). Endogenous heparinoids have been detected after variceal bleeding and during liver transplantation in some cirrhotics using heparinase-modified-TEG.

AIM

To assess if bacterial infection is associated with endogenous heparinoids in cirrhotics, thus impairing coagulation.

METHODS

Native and heparinase-modified-TEG (cleavage of heparin and heparan-sulphate) was performed in 60 cirrhotics (Grade A, 2; B, 30; C, 28): 30 infected [septicaemia, 6 (culture positive); 6 (culture negative); spontaneous bacterial peritonitis, 10; chest infection, 4; others, 4], 30 not infected, and five infected patients without liver diseases, comparing TEG parameters r, alpha, and ma. Eight cirrhotics were studied before and after infection. The diagnosis of presence and type of infection was based on international standard criteria.

RESULTS

A significant heparin effect was found only in infected cirrhotics (28 of 30) with significant changes in r (P=0.0003), alpha (P<0.0001), and ma (P<0.0001), but in none of those not infected. This effect completely reversed in the eight evaluated after resolution of infection. There was no heparin effect in infected non-cirrhotics.

CONCLUSIONS

A heparin effect was only found in cirrhotic patients with infection, further confirming that infection significantly modifies coagulation in cirrhotic patients.

Production of TNF-alpha by murine bone marrow derived mast cells activated by the bacterial fimbrial protein, FimH

Production of tumor necrosis factor alpha (TNF-alpha) by mast cells is an important aspect of host defense against gram negative bacteria. In order to define the intracellular pathways utilized by mast cells in this physiological, protective role, we have studied the production of TNF-alpha in bone marrow derived mast cells from the C3H/HeJ (LPS-insensitive) strain following exposure to bacteria expressing the fimbrial protein, FimH. Mast cells exposed to FimH produce TNF-alpha (300-1200 pg/10(6) cells) over 1-3 h compared with 1800-15,000 pg/10(6) cells produced by cells triggered via IgE/antigen. This low level of TNF-alpha production in vitro is compatible with the protective in vivo role of mast cells to produce modest amounts of TNF-alpha in contrast to the large amounts of mediators released during maximal activation. A second difference between the two signals is sensitivity to cyclosporin A (CsA). The IgE/antigen pathway is inhibited by 90-95% at 0.02 to 0.5 microM cyclosporin A whereas the FimH pathway is inhibited by only 40%. These data demonstrate that the intracellular pathway activated by FimH is different from that activated by IgE/antigen both in terms of amount of TNF-alpha produced and in sensitivity to CsA. This is the first evidence that FimH activates mast cells via a pathway that is distinct from that used by IgE/antigen.

P-selectin glycoprotein ligand-1 mediates rolling of mouse bone marrow-derived mast cells on P-selectin but not efficiently on E-selectin

It has been shown recently that mast cells play an essential role as a source of tumor necrosis factor-alpha production during neutrophil recruitment to sites of bacterial infection. Increased numbers of mast cells are indeed noted at sites of wound healing and inflammation. These cells are either recruited from the bone marrow or proliferate locally under cytokine stimulation. Little is known about how mast cell progenitors extravasate into tissue. Using antibody-like fusion proteins of mouse E-selectin and P-selectin, we have analyzed the ability of immature mouse bone marrow-derived mast cells (BMMC) to interact with the endothelial selectins. The P-selectin glycoprotein ligand-1 (PSGL-1) was affinity-isolated from detergent extracts of surface biotinylated BMMC with both selectin-IgG fusion proteins. However, only P-selectin-IgG, but not E-selectin-IgG showed significant interaction with intact BMMC as tested by flow cytometry and cell attachment assays with the immobilized fusion proteins under flow and non-flow conditions at physiological shear stress. Thus, in spite of carrying the necessary carbohydrate modifications which enable solubilized PSGL-1 to bind avidly to E-selectin, PSGL-1 on the surface of BMMC is presented in a way that prevents it from interacting efficiently with E-selectin. Affinity-purified rabbit antibodies against mouse PSGL-1 almost completely blocked the interaction of BMMC with P-selectin-IgG in flow cytometry as well as in cell adhesion assays under static and under flow conditions. Our data reveal that PSGL-1 is the major binding site for P-selectin on mouse BMMC progenitors, but does not support efficient interactions with E-selectin.