Influence of FAS on murine mast cell maturation

Update on Eosinophil Interaction with Mast Cells: The Allergic Effector Unit

Mast cells and eosinophils are the key effector cells of allergy [1]. In general, allergic reactions are composed of two phases, namely an early phase and a late phase, and after that resolution occurs. If the allergic reactions fail to resolve after the late phase, allergic inflammation (AI) can evolve into a chronic phase mainly involving mast cells and eosinophils that abundantly coexist in the inflamed tissue in the late and chronic phases and cross-talk in a bidirectional manner. We defined these bidirectional interactions between MCs and Eos, as the "allergic effector unit." This cross talk is mediated by both physical cell-cell contacts through cell surface receptors such as CD48, 2B4, and respective ligands and through released mediators such as various specific granular mediators, arachidonic acid metabolites, cytokines, and chemokines [2, 3]. The allergic effector unit can be studied in vitro in a customized co-culture system using mast cells and eosinophils derived from either mouse or human sources.

Controlling Mast Cell Activation and Homeostasis: Work Influenced by Bill Paul That Continues Today

Mast cells are tissue resident, innate immune cells with heterogenous phenotypes tuned by cytokines and other microenvironmental stimuli. Playing a protective role in parasitic, bacterial, and viral infections, mast cells are also known for their role in the pathogenesis of allergy, asthma, and autoimmune diseases. Here, we review factors controlling mast cell activation, with a focus on receptor signaling and potential therapies for allergic disease. Specifically, we will discuss our work with FcεRI and FγR signaling, IL-4, IL-10, and TGF-β1 treatment, and Stat5. We conclude with potential therapeutics for allergic disease. Much of these efforts have been influenced by the work of Bill Paul. With many mechanistic targets for mast cell activation and different classes of therapeutics being studied, there is reason to be hopeful for continued clinical progress in this area.

Peroxisome proliferator-activated receptor-β/δ modulates mast cell phenotype

The peroxisome proliferator-activated receptor-β/δ (PPARβ/δ) is known to have multiple anti-inflammatory effects, typically observed in endothelial cells, macrophages, T cells and B cells. Despite the fact that mast cells are important mediators of inflammation, to date, the role of PPARβ/δ in mast cells has not been examined. Hence, the present study examined the hypothesis that PPARβ/δ modulates mast cell phenotype. Bone-marrow-derived mast cells (BMMCs) and peritoneal mast cells from Pparβ/δ^+/+ mice expressed higher levels of high-affinity IgE receptor (FcεRI) compared with Pparβ/δ^-/- mice. BMMCs from Pparβ/δ^+/+ mice also exhibited dense granules, associated with higher expression of enzymes and proteases compared with Pparβ/δ^-/- mice. Resting BMMCs from Pparβ/δ^+/+ mice secreted lower levels of inflammatory cytokines, associated with the altered activation of phospholipase Cγ1 and extracellular signal-regulated kinases compared with Pparβ/δ^-/- mice. Moreover, the production of cytokines by mast cells induced by various stimuli was highly dependent on PPARβ/δ expression. This study demonstrates that PPARβ/δ is an important regulator of mast cell phenotype.

Effect of CD95 on inflammatory response in rheumatoid arthritis fibroblast-like synoviocytes

OBJECTIVE

Many CD95-expressing cells don't always undergo apoptosis after stimulation with CD95 ligation. The purpose of this paper is to investigate the role of expression of CD95 (Fas/Apo1) on inflammatory response in fibroblast-like synoviocytes (FLS) obtained from rheumatoid arthritis (RA) and to evaluate the role of phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PKB or Akt) pathways within this process.

METHODS

The expression levels of CD95 were monitored by immunohistochemistry and reverse transcription polymerase chain reaction (RT-PCR). Apoptotic cells were detected by in situ apoptosis detection (TUNEL) assay. The RA-FLS were treated with agonistic anti-CD95 antibody or CD95 siRNA. Then the proliferation was detected by CCK-8, and mRNA level of inflammatory cytokines was detected by RT-PCR. After the RA-FLS were treated with agonistic anti-CD95 antibody, the total Akt and pAkt protein expression was analyzed by Western blot, and the changes mentioned above were observed while pre-incubated with the PI3K inhibitor LY294002.

RESULTS

A significant increase of CD95 antigen was found in RA compared with osteoarthritis (OA) samples, while apoptosis in RA synovial tissue was not obvious. Low concentrations of agonistic anti-CD95 antibody could promote RA-FLS growth and interleukin-6 (IL-6) mRNA expression, while high concentrations could induce apoptosis. And both of these phenomena could be inhibited by CD95 siRNA. Agonistic anti-CD95 antibody could stimulate the expression of pAkt, and PI3K specific inhibitor LY294002 could induce opposite changes.

CONCLUSION

Stimulation of CD95 could promote RA-FLS proliferation and inflammation, and activation of the PI3K/Akt signaling pathway might be the possible mechanism.

Eosinophils interaction with mast cells: the allergic effector unit

Mast cells (MC) and eosinophils are the key effector cells of allergy (Minai-Fleminger and Levi-Schaffer, Inflamm Res 58:631-638, 2009). In general, allergic reactions have two phases, namely, an early phase and a late phase. MC and eosinophils abundantly coexist in the inflamed tissue in the late and chronic phases and cross talk in a bidirectional manner. This bidirectional interaction between MC and eosinophils is mediated by both physical cell-cell contacts through cell surface receptors such as CD48 receptors CD48, 2B4 , 2B4 and soluble mediators through various specific granular mediators, arachidonic acid metabolites, cytokines cytokines , and chemokines, collectively termed the "Allergic Effector Unit" (AEU) (Elishmereni et al., Allergy 66:376-385, 2011; Minai-Fleminger et al., Cell Tissue Res 341:405-415, 2010). These bidirectional interactions can be studied in vitro in a customized coculture system of MC and eosinophils derived from either mouse or human source.

Serglycin proteoglycan promotes apoptotic versus necrotic cell death in mast cells

The mechanisms that govern whether a cell dies by apoptosis or necrosis are not fully understood. Here we show that serglycin, a secretory granule proteoglycan of hematopoietic cells, can have a major impact on this decision. Wild type and serglycin(-/-) mast cells were equally sensitive to a range of cell death-inducing regimens. However, whereas wild type mast cells underwent apoptotic cell death, serglycin(-/-) cells died predominantly by necrosis. Investigations of the underlying mechanism revealed that cell death was accompanied by leakage of secretory granule compounds into the cytosol and that the necrotic phenotype of serglycin(-/-) mast cells was linked to defective degradation of poly(ADP-ribose) polymerase-1. Cells lacking mouse mast cell protease 6, a major serglycin-associated protease, exhibited similar defects in apoptosis as observed in serglycin(-/-) cells, indicating that the pro-apoptotic function of serglycin is due to downstream effects of proteases that are complex-bound to serglycin. Together, these findings implicate serglycin in promoting apoptotic versus necrotic cell death.