Differential release of histamine and prostaglandin D2 in rat peritoneal mast cells: roles of cytosolic calcium and protein tyrosine kinases

Mast cell-mediated neuroinflammation may have a role in attention deficit hyperactivity disorder (Review)

Attention deficit hyperactivity disorder (ADHD) is a common neurodevelopmental and behavioral disorder with a serious negative impact on the quality of life from childhood until adulthood, which may cause academic failure, family disharmony and even social unrest. The pathogenesis of ADHD has remained to be fully elucidated, leading to difficulties in the treatment of this disease. Genetic and environmental factors contribute to the risk of ADHD development. Certain studies indicated that ADHD has high comorbidity with allergic and autoimmune diseases, with various patients with ADHD having a high inflammatory status. Increasing evidence indicated that mast cells (MCs) are involved in the pathogenesis of brain inflammation and neuropsychiatric disorders. MCs may cause or aggravate neuroinflammation via the selective release of inflammatory factors, interaction with glial cells and neurons, activation of the hypothalamic-pituitary adrenal axis or disruption of the blood-brain barrier integrity. In the present review, the notion that MC activation may be involved in the occurrence and development of ADHD through a number of ways is discussed based on previously published studies. The association between MCs and ADHD appears to lack sufficient evidence at present and this hypothesis is considered to be worthy of further study, providing a novel perspective for the treatment of ADHD.

Mast Cell Histamine-Induced Calcium Transients in Cultured Human Peritoneal Mesothelial Cells

Objective

Peritoneal inflammation results from a complex interplay of events initiated by macrophage activity in response to infection, with the stimulation of mesothelial cell cytokine release amplifying the recruitment of blood-borne defense cells to the site of injury. Resident peritoneal mast cells may add to this complexity with mast cell derived cytokines released during this cascade. This study examined the influence of histamine, a mast cell derived inflammatory mediator, on the initial activation of human peritoneal mesothelial cells (HPMC) by intracellular free calcium (Cai2+) mobilization, and changes to the actin cytoskeleton.

Design

HPMC signal transduction was examined in response to histamine (1.0 mmol/L) compared to fetal bovine serum (FBS) (0.1 %) and 4-br-A23187 (1.0 μmol/L). Intracellular free calcium was measured in fura-2 loaded cells with and without external calcium (Ca2ex+t), or Ca2ex+t with verapamil (100 μmol/L). Following treatment with agonists, HPMC actin cytoskeleton was stained using direct immunocytochemistry.

Results

HPMC responded to histamine with a twofold transient rise in Cai2+ which returned to the baseline, in contrast with FBS and A23187–induced Cai2+ transients, which returned to elevated resting values. In the absence of Ca2ex+t’ all agents produced a calcium transient indicative of calcium release from intracellular stores. Histamine induced calcium -dependent changes to the cytoskeleton and cellular organization, including increased actin stress fibers.

Conclusion

Histamine produced large specific receptor-mediated calcium transients in HPMC, which included components of calcium release from intracellular stores and receptor -mediated calcium influx processes. The observed response to histamine raises the possibility that histamine derived from resident mast cells may modulate mesothelial cell function, in part by calciumdependent pathways, and influence the performance of the peritoneal membrane during peritoneal dialysis.

Mast cell degranulation by a hemolytic lipid toxin decreases GBS colonization and infection

Ascending infection of microbes from the lower genital tract into the amniotic cavity increases the risk of preterm birth, stillbirth, and newborn infections. Host defenses that are critical for preventing ascending microbial infection are not completely understood. Group B Streptococcus (GBS) are Gram-positive bacteria that frequently colonize the lower genital tract of healthy women but cause severe infections during pregnancy, leading to preterm birth, stillbirth, or early-onset newborn infections. We recently described that the GBS pigment is hemolytic, and increased pigment expression promotes GBS penetration of human placenta. Here, we show that the GBS hemolytic pigment/lipid toxin and hyperpigmented GBS strains induce mast cell degranulation, leading to the release of preformed and proinflammatory mediators. Mast cell-deficient mice exhibit enhanced bacterial burden, decreased neutrophil mobilization, and decreased immune responses during systemic GBS infection. In a vaginal colonization model, hyperpigmented GBS strains showed increased persistence in mast cell-deficient mice compared to mast cell-proficient mice. Consistent with these observations, fewer rectovaginal GBS isolates from women in their third trimester of pregnancy were hyperpigmented/hyperhemolytic. Our work represents the first example of a bacterial hemolytic lipid that induces mast cell degranulation and emphasizes the role of mast cells in limiting genital colonization by hyperpigmented GBS.

The Role of TRP Proteins in Mast Cells

Transient receptor potential (TRP) proteins form cation channels that are regulated through strikingly diverse mechanisms including multiple cell surface receptors, changes in temperature, in pH and osmolarity, in cytosolic free Ca(2+) concentration ([Ca(2+)](i)), and by phosphoinositides which makes them polymodal sensors for fine tuning of many cellular and systemic processes in the body. The 28 TRP proteins identified in mammals are classified into six subfamilies: TRPC, TRPV, TRPM, TRPA, TRPML, and TRPP. When activated, they contribute to cell depolarization and Ca(2+) entry. In mast cells, the increase of [Ca(2+)](i) is fundamental for their biological activity, and several entry pathways for Ca(2+) and other cations were described including Ca(2+) release activated Ca(2+) (CRAC) channels. Like in other non-excitable cells, TRP channels could directly contribute to Ca(2+) influx via the plasma membrane as constituents of Ca(2+) conducting channel complexes or indirectly by shifting the membrane potential and regulation of the driving force for Ca(2+) entry through independent Ca(2+) entry channels. Here, we summarize the current knowledge about the expression of individual Trp genes with the majority of the 28 members being yet identified in different mast cell models, and we highlight mechanisms how they can regulate mast cell functions. Since specific agonists or blockers are still lacking for most members of the TRP family, studies to unravel their function and activation mode still rely on experiments using genetic approaches and transgenic animals. RNAi approaches suggest a functional role for TRPC1, TRPC5, and TRPM7 in mast cell derived cell lines or primary mast cells, and studies using Trp gene knock-out mice reveal a critical role for TRPM4 in mast cell activation and for mast cell mediated cutaneous anaphylaxis, whereas a direct role of cold- and menthol-activated TRPM8 channels seems to be unlikely for the development of cold urticaria at least in mice.

Mast cells and inflammation

Mast cells are well known for their role in allergic and anaphylactic reactions, as well as their involvement in acquired and innate immunity. Increasing evidence now implicates mast cells in inflammatory diseases where they are activated by non-allergic triggers, such as neuropeptides and cytokines, often exerting synergistic effects as in the case of IL-33 and neurotensin. Mast cells can also release pro-inflammatory mediators selectively without degranulation. In particular, IL-1 induces selective release of IL-6, while corticotropin-releasing hormone secreted under stress induces the release of vascular endothelial growth factor. Many inflammatory diseases involve mast cells in cross-talk with T cells, such as atopic dermatitis, psoriasis and multiple sclerosis, which all worsen by stress. How mast cell differential responses are regulated is still unresolved. Preliminary evidence suggests that mitochondrial function and dynamics control mast cell degranulation, but not selective release. Recent findings also indicate that mast cells have immunomodulatory properties. Understanding selective release of mediators could explain how mast cells participate in numerous diverse biologic processes, and how they exert both immunostimulatory and immunosuppressive actions. Unraveling selective mast cell secretion could also help develop unique mast cell inhibitors with novel therapeutic applications. This article is part of a Special Issue entitled: Mast cells in inflammation.

Regulators of Ca(2+) signaling in mast cells: potential targets for treatment of mast cell-related diseases?

A calcium signal is essential for degranulation, generation of eicosanoids and optimal production of cytokines in mast cells in response to antigen and other stimulants. The signal is initiated by phospholipase C-mediated production of inositol1,4,5-trisphosphate resulting in release of stored Ca(2+) from the endoplasmic reticulum (ER) and Golgi. Depletion of these stores activates influx of extracellular Ca(2+), usually referred to as store-operated calcium entry (SOCE), through the interaction of the Ca(2+)-sensor, stromal interacting molecule-1 (STIM1 ), in ER with Orai1(CRACM1) and transient receptor potential canonical (TRPC) channel proteins in the plasma membrane (PM). This interaction is enabled by microtubular-directed reorganization of ER to form ER/PM contact points or "punctae" in which STIM1 and channel proteins colocalize. The ensuing influx of Ca(2+) replenishes Ca(2+) stores and sustains elevated levels of cytosolic Ca(2+) ions-the obligatory signal for mast-cell activation. In addition, the signal can acquire spatial and dynamic characteristics (e.g., calcium puffs, waves, oscillations) that encode signals for specific functional outputs. This is achieved by coordinated regulation of Ca(2+) fluxes through ATP-dependent Ca(2+)-pumps and ion exchangers in mitochondria, ER and PM. As discussed in this chapter, studies in mast cells revealed much about the mechanisms described above but little about allergic and autoimmune diseases although studies in other types of cells have exposed genetic defects that lead to aberrant calcium signaling in immune diseases. Pharmacologic agents that inhibit or activate the regulatory components of calcium signaling in mast cells are also discussed along with the prospects for development of novel SOCE inhibitors that may prove beneficial in the treatment inflammatory mast-cell related diseases.

Regulation of mast cell responses in health and disease

Mast cells are multifunctional cells that initiate not only IgE-dependent allergic diseases but also play a fundamental role in innate and adaptive immune responses to microbial infection. They are also thought to play a role in angiogenesis, tissue remodeling, wound healing, and tumor repression or growth. The broad scope of these physiologic and pathologic roles illustrates the flexible nature of mast cells, which is enabled in part by their phenotypic adaptability to different tissue microenvironments and their ability to generate and release a diverse array of bioactive mediators in response to multiple types of cell-surface and cytosolic receptors. There is increasing evidence from studies in cell cultures that release of these mediators can be selectively modulated depending on the types or groups of receptors activated. The intent of this review is to foster interest in the interplay among mast cell receptors to help understand the underlying mechanisms for each of the immunological and non-immunological functions attributed to mast cells. The second intent of this review is to assess the pathophysiologic roles of mast cells and their products in health and disease. Although mast cells have a sufficient repertoire of bioactive mediators to mount effective innate and adaptive defense mechanisms against invading microorganisms, these same mediators can adversely affect surrounding tissues in the host, resulting in autoimmune disease as well as allergic disorders.

Regulation of Ca2+ signaling with particular focus on mast cells

Calcium signals mediate diverse cellular functions in immunological cells. Early studies with mast cells, then a preeminent model for studying Ca2+-dependent exocytosis, revealed several basic features of calcium signaling in non-electrically excitable cells. Subsequent studies in these and other cells further defined the basic processes such as inositol 1,4,5-trisphosphate-mediated release of Ca2+ from Ca2+ stores in the endoplasmic reticulum (ER); coupling of ER store depletion to influx of external Ca2+ through a calcium-release activated calcium (CRAC) channel now attributed to the interaction of the ER Ca2+ sensor, stromal interacting molecule-1 (STIM1), with a unique Ca2+-channel protein, Orai1/CRACM1, and subsequent uptake of excess Ca2+ into ER and mitochondria through ATP-dependent Ca2+ pumps. In addition, transient receptor potential channels and ion exchangers also contribute to the generation of calcium signals that may be global or have dynamic (e.g., waves and oscillations) and spatial resolution for specific functional readouts. This review discusses past and recent developments in this field of research, the pharmacologic agents that have assisted in these endeavors, and the mast cell as an exemplar for sorting out how calcium signals may regulate multiple outputs in a single cell.

Differential release of mast cell mediators and the pathogenesis of inflammation

Mast cells are well known for their involvement in allergic and anaphylactic reactions, during which immunoglobulin E (IgE) receptor (Fc epsilon RI) aggregation leads to exocytosis of the content of secretory granules (1000 nm), commonly known as degranulation, and secretion of multiple mediators. Recent findings implicate mast cells also in inflammatory diseases, such as multiple sclerosis, where mast cells appear to be intact by light microscopy. Mast cells can be activated by bacterial or viral antigens, cytokines, growth factors, and hormones, leading to differential release of distinct mediators without degranulation. This process appears to involve de novo synthesis of mediators, such as interleukin-6 and vascular endothelial growth factor, with release through secretory vesicles (50 nm), similar to those in synaptic transmission. Moreover, the signal transduction steps necessary for this process appear to be largely distinct from those known in Fc epsilon RI-dependent degranulation. How these differential mast cell responses are controlled is still unresolved. No clinically available pharmacological agents can inhibit either degranulation or mast cell mediator release. Understanding this process could help develop mast cell inhibitors of selective mediator release with novel therapeutic applications.

Antimicrobial peptides human beta-defensin (hBD)-3 and hBD-4 activate mast cells and increase skin vascular permeability

Antimicrobial peptides human beta-defensins (hBD) are mainly produced by epithelia of several organs including skin, and participate in innate immunity by killing invading pathogens. Besides their microbicidal activities, hBD activate several inflammatory and immune cells. Since hBD are generated by tissues where mast cells are present, we hypothesized that these peptides could activate mast cells. In this study, we demonstrated that both hBD-3 and hBD-4 induced mast cell degranulation, prostaglandin D2 production, intracellular Ca2+ mobilization and chemotaxis. Furthermore, hBD-3- and hBD-4-induced activation of mast cells was suppressed by pertussis toxin and U-73122, inhibitors for G protein and phospholipase C, respectively. We further revealed that hBD-3 and hBD-4 increased vascular permeability in the skin, which was dependent on the presence of mast cells, because hBD-3 and hBD-4 failed to enhance vascular permeability in mast cell-deficient Ws/Ws rats. We also demonstrated that hBD-3 and hBD-4 induced phosphorylation of MAPK p38 and ERK1/2, which were further required for hBD-mediated mast cell activation, as evidenced by the inhibitory effects of p38 and ERK1/2 inhibitors on mast cell degranulation. Together, these findings suggest the key role of hBD in inflammatory responses by recruiting and activating mast cells, and increasing vascular permeability.

Human umbilical cord blood-derived mast cells: a unique model for the study of neuro-immuno-endocrine interactions

Findings obtained using animal models have often failed to reflect the processes involved in human disease. Moreover, human cultured cells do not necessarily function as their actual tissue counterparts. Therefore, there is great demand for sources of human progenitor cells that may be directed to acquire specific tissue characteristics and be available in sufficient quantities to carry out functional and pharmacological studies. Acase in point is the mast cell, well known for its involvement in allergic reactions, but also implicated in inflammatory diseases. Mast cells can be activated by allergens, anaphylatoxins, immunoglobulin-free light chains, superantigens, neuropeptides, and cytokines, leading to selective release of mediators. These could be involved in many inflammatory diseases, such as asthma and atopic dermatitis, which worsen by stress, through activation by local release of corticotropin-releasing hormone or related peptides. Umbilical cord blood and cord matrix-derived mast cell progenitors can be separated magnetically and grown in the presence of stem cell factor, interleukin-6, interleukin-4, and other cytokines to yield distinct mast cell populations. The recent use of live cell array, with its ability to study such interactions rapidly at the single-cell level, provides unique new opportunities for fast output screening of mast cell triggers and inhibitors.

The critical role of mast cells in allergy and inflammation

Mast cells are well known for their involvement in allergic and anaphylactic reactions, but recent findings implicate them in a variety of inflammatory diseases affecting different organs, including the heart, joints, lungs, and skin. In these cases, mast cells appear to be activated by triggers other than aggregation of their IgE receptors (FcepsilonRI), such as anaphylatoxins, immunoglobulin-free light chains, superantigens, neuropeptides, and cytokines leading to selective release of mediators without degranulation. These findings could explain inflammatory diseases, such as asthma, atopic dermatitis, coronary inflammation, and inflammatory arthritis, all of which worsen by stress. It is proposed that the pathogenesis of these diseases involve mast cell activation by local release of corticotropin-releasing hormone (CRH) or related peptides. Combination of CRH receptor antagonists and mast cell inhibitors may present novel therapeutic interventions.

Differential activation of the PI 3-kinase effectors AKT/PKB and p70 S6 kinase by compound 48/80 is mediated by PKCα

The secretagogue compound 48/80 (c48/80) is a well known activator of calcium mediated processes and PKCs, and is a potent inducer of mast cell degranulation. As the latter process is a phosphoinositide 3-kinase (PI 3-kinase) mediated event, we wished to address whether or not c48/80 was an activator of PI 3-kinases. The data presented here reveal that c48/80 is an effective activator of PI 3-kinases as judged by the increased phosphorylation of PKB and p70(S6K) in fibroblasts in a PI 3-kinase dependent fashion. Compound 48/80 effectively translocates PKB to the plasma membrane and induces phosphorylation at serine 473 (S473), detected by fluorescence imaging of fixed cells. At higher concentrations the secretagogue is inhibitory towards PKB phosphorylation on S473. Conversely, p70(S6K) phosphorylation on T389 is unaffected at high doses. We provide evidence that the differential effect on the two PI 3-kinase effectors is due to activation of PKCalpha by c48/80, itself a PI 3-kinase dependent process. We conclude that compound 48/80 is an effective activator of PI 3-kinase dependent pathways, leading to the activation of effectors including PKB/Akt, p70(S6K) and PKCalpha. The latter is only activated by higher doses of c48/80 resulting in an inhibition of the c48/80 induced PKB phosphorylation, thus explaining the observed biphasic activation profile for PKB in response to this secretagogue.

Kounis syndrome (allergic angina and allergic myocardial infarction): a natural paradigm?

Inflammatory mediators including histamine, neutral proteases, arachidonic acid products, platelet activating factor and a variety of cytokines and chemokines are increased in blood or urine in both allergic episodes and acute coronary syndromes. The release of mediators during allergic insults has been incriminated to induce coronary artery spasm and/or atheromatous plaque erosion or rupture. A common pathway between allergic and non-allergic coronary syndromes seems to exist. Today, there is evidence that mast cells not only enter the culprit region before plaque erosion or rupture but they release their contents before an actual coronary episode. Kounis syndrome is the concurrence of acute coronary syndromes with conditions associated with mast cell activation including allergic or hypersensitivity and anaphylactic or anaphylactoid insults. It is caused by inflammatory mediators released through mast cell activation. Kounis syndrome, as consequence, of the above pathophysiologic association is regarded as nature's own experiment and magnificent natural paradigm showing novel way in an effort to prevent acute coronary syndromes. Drugs and natural molecules which stabilize mast cell membrane and monoclonal antibodies that protect mast cell surface could emerge as novel therapeutic modalities capable to prevent acute coronary and cerebrovascular events.

The role of mast cells in migraine pathophysiology

Mast cells are critical players in allergic reactions, but they have also been shown to be important in immunity and recently also in inflammatory diseases, especially asthma. Migraines are episodic, typically unilateral, throbbing headaches that occur more frequently in patients with allergy and asthma implying involvement of meningeal and/or brain mast cells. These mast cells are located perivascularly, in close association with neurons especially in the dura, where they can be activated following trigeminal nerve, as well as cervical or sphenopalatine ganglion stimulation. Neuropeptides such as calcitonin gene-related peptide (CGRP), hemokinin A, neurotensin (NT), pituitary adenylate cyclase activating peptide (PACAP), and substance P (SP) activate mast cells leading to secretion of vasoactive, pro-inflammatory, and neurosensitizing mediators, thereby contributing to migraine pathogenesis. Brain mast cells can also secrete pro-inflammatory and vasodilatory molecules such as interleukin-6 (IL-6) and vascular endothelial growth factor (VEGF), selectively in response to corticotropin-releasing hormone (CRH), a mediator of stress which is known to precipitate or exacerbate migraines. A better understanding of brain mast cell activation in migraines would be useful and could lead to several points of prophylactic intervention.

Critical role of mast cells in inflammatory diseases and the effect of acute stress

Mast cells are not only necessary for allergic reactions, but recent findings indicate that they are also involved in a variety of neuroinflammatory diseases, especially those worsened by stress. In these cases, mast cells appear to be activated through their Fc receptors by immunoglobulins other than IgE, as well as by anaphylatoxins, neuropeptides and cytokines to secrete mediators selectively without overt degranulation. These facts can help us better understand a variety of sterile inflammatory conditions, such as multiple sclerosis (MS), migraines, inflammatory arthritis, atopic dermatitis, coronary inflammation, interstitial cystitis and irritable bowel syndrome, in which mast cells are activated without allergic degranulation.

Activation of betagamma subunits of G(i2) and G(i3) proteins by basic secretagogues induces exocytosis through phospholipase Cbeta and arachidonate release through phospholipase Cgamma in mast cells

Mast cells are activated by Ag-induced clustering of IgE bound to FcepsilonRI receptors or by basic secretagogues that stimulate pertussis toxin-sensitive heterotrimeric G proteins. The cell response includes the secretion of stored molecules, such as histamine, through exocytosis and of de novo synthesized mediators, such as arachidonate metabolites. The respective roles of G proteins alpha and betagamma subunits as well as various types of phospholipase C (PLC) in the signaling pathways elicited by basic secretagogues remain unknown. We show that a specific Ab produced against the C-terminus of Galpha(i3) and an anti-recombinant Galpha(i2) Ab inhibited, with additive effects, both exocytosis and arachidonate release from permeabilized rat peritoneal mast cells elicited by the basic secretagogues mastoparan and spermine. A specific Ab directed against Gbetagamma dimers prevented both secretions. Anti-PLCbeta Abs selectively prevented exocytosis. The selective phosphatidylinositol 3-kinase inhibitor LY 294002 prevented arachidonate release without modifying exocytosis. Gbetagamma coimmunoprecipitated with PLCbeta and phosphatidylinositol 3-kinase. The anti-PLCgamma1 and anti-phospholipase A(2) Abs selectively blocked arachidonate release. Protein tyrosine phosphorylation was inhibited by anti-Gbetagamma Abs, LY294002, and anti PLCgamma1 Abs. These data show that the early step of basic secretagogue transduction is common to both signaling pathways, involving betagamma subunits of G(i2) and G(i3) proteins. Activated Gbetagamma interacts, on one hand, with PLCbeta to elicit exocytosis and, on the other hand, with phosphatidylinositol 3-kinase to initiate the sequential activation of PLCgamma1, tyrosine kinases, and phospholipase A(2), leading to arachidonate release.

Evaluation of the effects of peptide antibiotics human beta-defensins-1/-2 and LL-37 on histamine release and prostaglandin D(2) production from mast cells

Antimicrobial peptides, human beta-defensins (hBD-1/-2), and LL-37 (a peptide of human cathelicidin CAP18) are predominately expressed at epithelial tissues, where they participate in the innate host defense by killing invading microorganisms. In this study, to investigate the interactions between epithelial cell-derived antimicrobial peptides and mast cells, we evaluated the effects of hBD-1/-2 and LL-37 on mast cell functions using rat peritoneal mast cells. hBD-2 and LL-37 but not hBD-1 induced histamine release and intracellular Ca(2+) mobilization, and hBD-2 was more potent than LL-37. Interestingly, histamine release and intracellular Ca(2+) mobilization elicited by hBD-2 and LL-37 were markedly suppressed by BAPTA-AM (an intracellular Ca(2+) chelating agent), pertussis toxin and U-73122 (a phospholipase C inhibitor). In addition, among the peptides examined, only hBD-2 significantly induced PGD(2) production, which was abolished by indomethacin (cyclooxygenase-1/-2 inhibitor) but not NS-398 (cyclooxygenase-2 inhibitor), suggesting that hBD-2-induced PGD(2) production is mediated by cyclooxygenase-1. Likewise, the PGD(2) production was suppressed by pertussis toxin and U-73122. These observations suggest that hBD-2 and LL-37 stimulate mast cells to mobilize intracellular Ca(2+) and release histamine or generate PGD(2) in a G protein-phospholipase C-dependent manner. Thus, hBD-2 and LL-37 may have modulatory effects on inflammatory reactions.

Chondroitin sulphate inhibits connective tissue mast cells

1. Mast cells derive from the bone marrow and are responsible for the development of allergic and possibly inflammatory reactions. Mast cells are stimulated by immunoglobulin E (IgE) and specific antigen, but also by a number of neuropeptides such as neurotensin (NT), somatostatin or substance P (SP), to secrete numerous pro-inflammatory molecules that include histamine, cytokines and proteolytic enzymes. 2. Chondroitin sulphate, a major constituent of connective tissues and of mast cell secretory granules, had a dose-dependent inhibitory effect on rat peritoneal mast cell release of histamine induced by the mast cell secretagogue compound 48/80 (48/80). This inhibition was stronger than that of the clinically available mast cell 'stabilizer' disodium cromoglycate (cromolyn). Inhibition by chondroitin sulphate increased with the length of preincubation and persisted after the drug was washed off, while the effect of cromolyn was limited by rapid tachyphylaxis. 3. Immunologic stimulation of histamine secretion from rat connective tissue mast cells (CTMC) was also inhibited, but this effect was weaker in umbilical cord-derived human mast cells and was absent in rat basophilic leukemia (RBL) cells which are considered homologous to mucosal mast cells (MMC). Oligo- and monosaccharides were not as effective as the polysaccharides. 4. Inhibition, documented by light and electron microscopy, involved a decrease of intracellular calcium ion levels shown by confocal microscopy and image analysis. Autoradiography at the ultrastructural level showed that chondroitin sulphate was mostly associated with plasma and perigranular membranes. 5. Chondroitin sulphate appears to be a potent mast cell inhibitor of allergic and nonimmune stimulation with potential clinical implications.

Basic secretagogues activate protein tyrosine phosphorylation and release of arachidonic acid in mast cells via a novel protein kinase C and phosphatidylinositol 3-kinase-dependent mechanism

Mast cells play a central role in inflammatory and immediate-type allergic reactions. These granulated cells release by a process of regulated exocytosis a variety of biologically active substances which are either preformed (e.g. histamine), or synthesized de novo following activation [e. g. metabolites of arachidonic acid (AA) and multifunctional cytokines]. Exocytosis in mast cells is activated either in response to aggregation of the receptors for immunoglobulin E (FcepsilonRI) or by the direct activation of pertussis toxin-sensitive G-proteins by a class of receptor mimetic agents, collectively known as basic secretagogues of mast cells. In the present study we show that compound 48/80 (c48/80), a synthetic member of the class of basic secretagogues, stimulates protein tyrosine phosphorylation of a number of as yet unidentified cellular substrates. These phosphorylations were inhibited by the tyrphostin AG-18, by the phosphatidylinositol 3-kinase inhibitor wortmannin and by the protein kinase C inhibitors K252a and GF1 09203X. These inhibitors also inhibited the release of AA induced by c48/80 but had no effect on exocytosis. Taken together, our findings suggest that basic secretagogues induce protein tyrosine phosphorylation as part of their parallel multiple signaling pathways which are presumably mediated by more than one G-protein. Both protein kinase C and phosphatidylinositol 3-kinase serve as intermediates in this signaling pathway. The protein tyrosine kinase signaling pathway, which mediates the activation of AA release, does not contribute to secretion of the preformed mediators such as histamine, but it might largely contribute to the de novo production of inflammatory mediators like leukotrienes and prostaglandins.

Heart EC respond heterogeneous on cytokine stimulation in ICAM-1 and VCAM-1, but not in MHC expression. A study with 3 rat heart endothelial cell (RHEC) lines

Cytokine-induced expression of ICAM-1, VCAM-1, and MHC class I and II was studied at different time points in microvascular endothelial cells (EC) of heart origin, using three different rat endothelial cell (RHEC) lines that were stimulated with TNFalpha and/or IFNgamma. Each of the three RHEC lines responded to TNFalpha as well as to IFNgamma; stimulation with combined cytokines led to increased or even synergistic effects. TNFalpha was most potent in inducing ICAM-1 and VCAM-1, whereas MHC class II was most effectively induced by IFNgamma. The 3 RHEC lines responded similarly regarding induction of MHC class II and upregulation of constitutively expressed MHC class I on the cells. However, the RHEC lines showed remarkable differences with respect to ICAM-1 and VCAM-1 induction, with each line having a unique expression profile. In RHEC-3, both ICAM-1 and VCAM-1 were well inducible, whereas in RHEC-10, no ICAM-1 and only some VCAM-1 could be induced. RHEC-11 showed minimal induction of ICAM-1, but strong induction of VCAM-1. For P-selectin induction, no such differences were found between the RHEC lines. These heterogeneous effects of cytokine stimulation could neither be explained by differences in mobilization of calcium nor by ultra-structural differences between the lines. Stimulation of the RHEC lines for ICAM-1 and VCAM-1 or MHC class II molecule induction resulted in expressing and non-expressing EC. Experiments with selected and subsequently cultured expressing and non-expressing cell populations for either ICAM-1, VCAM-1 or MHC class II, indicated that this selective induction most likely results from intrinsic regulation mechanisms in the cell cultures, and not from the presence of particular EC subpopulations within the lines. We conclude that microvascular heart endothelial cells, as represented by the 3 RHEC lines, demonstrate a selective heterogeneity in expression of ICAM-1 and VCAM-1, but not of MHC class I and II, upon cytokine stimulation. The consequences of this heterogeneity for leukocyte-endothelial cell interactions in heart inflammation and immune reactivity is discussed.

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.

Effects of three different Ca(2+)-ATPase inhibitors on Ca2+ response and leukotriene release in RBL-2H3 cells

The effects of three Ca(2+)-ATPase inhibitors, thapsigargin (TG), cyclopiazonic acid (CPA), and 2,5-di(tert-butyl)-1,4-hydroquinone (DTBHQ), on the Ca2+ response, degranulation, and leukotriene C4 (LTC4) release in RBL-2H3 cells were investigated. All three compounds elevated the intracellular free Ca2+ concentration ([Ca2+]i), and caused degranulation in the presence of 12-O-tetradecanoylphorbol-13-acetate (TPA), a protein kinase C activator. The dose-dependency of each compound in the Ca2+ response was in good agreement with that in degranulation. TG and CPA also caused the release of LTC4 in a dose-dependent manner, and this effect was unaffected by TPA or calphostin C, a selective PKC inhibitor. DTBHQ, however, did not induce LTC4 release, and rather inhibited the antigen-induced release of LTC4. These results suggest [1] that both degranulation and LTC4 release caused by these compounds are dependent on their [Ca2+]i increasing effect, [2] that degranulation and LTC4 release are mediated via independent pathways following the Ca2+ response, and [3] that DTBHQ additionally prevents the synthesis of LTC4 possibly by inhibition of 5-lipoxygenase.