2,4,6-Trihydroxy-alpha-p-methoxyphenylacetophenone (Compound D-58) is a potent inhibitor of allergic reactions

The authors investigated the effects of 2,4,6-trihydroxy-alpha-p-methoxyphenylacetophenone (compound D-58), a potent inhibitor of protein tyrosine kinases SYK and Bruton's tyrosine kinase (BTK), on IgE receptor/FcepsilonRI-triggered mast cell-mediated acute allergic responses in vitro and in vivo. Compound D-58 abrogated IgE receptor/FcepsilonRI-mediated SYK and BTK activation as well as calcium mobilization in mast cells. Mast-cell degranulation and leukotriene (LT) C(4) release was inhibited by compound D-58 in a concentration-dependent fashion. Notably, compound D-58 prevented the mast cell mediator-induced vascular hyperpermeability in an in vivo murine model of passive cutaneous anaphylaxis as measured by the prevention of extravasation of systemically administered Evans blue dye. The results uniquely indicate that compound D-58 has potent antiallergic properties. Therefore, further development of compound D-58 may provide the basis for new and effective treatment programs for severe allergic disorders.

Leflunomide metabolite analogue alpha-cyano-beta-hydroxy-beta-methyl-N-[3-(trifluoromethyl)phenyl]propenamide inhibits IgE/FcepsilonRI receptor-mediated mast cell leukotriene release and allergic asthma in mice

Mast cell-derived leukotrienes (LTs) play a critical role in the pathophysiology of allergy and asthma. We synthesized 13 analogues of leflunomide (LFM) and examined their in vitro effects on IgE/FcepsilonRI receptor-mediated mast cell LT release. We observed that the novel LFM analogue, alpha-cyano-beta-hydroxy-beta-methyl-N-[3-(trifluoromethyl) phenyl]propenamide (LFM-A8), is a more potent inhibitor than LFM of IgE/FcepsilonRI receptor-mediated LTC4 release from RBL-2H3 rat mast cells. Notably, LFM-A8 showed promising biologic activity in a mouse model of allergic asthma. Treatment of ovalbumin (OVA)-sensitized mice with LFM-A8 prevented the development of airway hyperresponsiveness to methacholine in a dose-dependent fashion. Furthermore, LFM-A8 inhibited the eosinophil recruitment to the airway lumen after the OVA challenge in a dose-dependent fashion. Therefore further development of compound LFM-A8 may provide the basis for new and effective treatment programs for severe allergic disorders, including allergic asthma.

Role of Janus kinase 3 in mast cell-mediated innate immunity against gram-negative bacteria

Mast cells play a pivotal role in innate host immune response to gram-negative bacteria. We report that Janus kinase 3 plays a role in mast cell-mediated bacterial clearance and neutrophil recruitment by regulating the release of tumor necrosis factor from mast cells. The role of JAK3 in mast cell-facilitated neutrophil recruitment and bacterial clearance was investigated by comparing the neutrophil influxes and bacterial clearance in mast cell-deficient W/W(v) mice reconstituted with JAK3(+/+) or JAK(-/-) mast cells. The neutrophil influx, bacterial clearance, and survival outcome in W/W(v) mice reconstituted with JAK3(+/+) mast cells was better than in W/W(v) mice reconstituted with JAK3(-/-) mast cells. These findings provide evidence that JAK3 is a key regulator of mast cell-mediated innate immunity against gram-negative bacteria.

Anti-inflammatory activity of 2,4, 6-trihydroxy-alpha-p-methoxyphenyl-acetophenone (compound D-58)

BACKGROUND

Active oxygen radicals as well as a variety of cytosolic protein tyrosine kinases play a role in the regulation of prostaglandin E(2) (PGE(2)), a key inflammatory mediator, released by skin cells in response to irradiation with ultraviolet B light (UVB). Identification of chemical compounds that can interrupt such events may provide a basis for the development of potent anti-inflammatory agents.

OBJECTIVE

To investigate the effect of a novel genistein analog, 2,4, 6-trihydroxy-alpha-p-methoxyphenylacetophenone, with antioxidant property (compound D-58), on UVB-induced inflammatory responses.

METHODS

Epidermal cell cultures were irradiated with UVB both in the presence and absence of compound D-58 and the PGE(2) released in the medium was determined by ELISA. For in vivo studies, skin inflammation was induced in mice either by carrageenan challenge of the air pouch or by an acute exposure of skin to UVB radiation. The resulting inflammatory mediator release, skin edema and the histological changes of the skin were determined both in the presence and absence of compound D-58.

RESULTS

Compound D-58 treatment effectively inhibited the development of edema and histological changes in the skin of UVB-irradiated mice as well as the release of PGE(2) in vitro as well as in vivo.

CONCLUSION

Compound D-58 (2,4,6-trihydroxy-alpha-p-methoxyphenylacetophenone) has potent anti-inflammatory properties.

Mast cell modulation of immune responses to bacteria

Mast cells are key elements of the immune system. These cells release a wide variety of pro-inflammatory mediators which are responsible for the pathophysiology of many allergic diseases. Recent studies, however, have shown that mast cells have the capacity to modulate the host's innate immune response to gram negative bacteria by their ability to phagocytose bacteria, process and present bacterial antigens to T cells and recruit phagocytic help through the release of physiological amounts of pro-inflammatory mediators. Here, current knowledge of mast cell responses to gram negative bacteria and molecular mechanisms associated with mast cell bacteria interaction is reviewed.

Treatment of allergic asthma by targeting janus kinase 3-dependent leukotriene synthesis in mast cells with 4-(3', 5'-dibromo-4'-hydroxyphenyl)amino-6,7-dimethoxyquinazoline (WHI-P97)

4-(3',5'-Dibromo-4'-hydroxyphenyl)amino-6,7-dimethoxyquinazoline (WHI-P97) is a rationally designed potent inhibitor of Janus kinase (JAK)-3. Treatment of mast cells with WHI-P97 inhibited the translocation of 5-lipoxygenase (5-LO) from the nucleoplasm to the nuclear membrane and consequently 5-LO-dependent leukotriene (LT) synthesis after IgE receptor/FcepsilonRI crosslinking by >90% at low micromolar concentrations. WHI-P97 did not directly inhibit the enzymatic activity of 5-LO, but prevented its translocation to the nuclear membrane without affecting the requisite calcium signal. WHI-P97 was very well tolerated in mice, with no signs of toxicity at dose levels ranging from 5 microg/kg to 50 mg/kg, and LD(10) was not reached at a 50 mg/kg dose level when administered as a single i. p. or i.v. bolus dose. Therapeutic WHI-P97 concentrations, which inhibit mast cell leukotriene synthesis in vitro, could easily be achieved in vivo after the i.v. or i.p. administration of a single nontoxic 40 mg/kg bolus dose of WHI-P97. Notably, WHI-P97 showed promising biological activity in a mouse model of allergic asthma at nontoxic dose levels. Treatment of ovalbumin-sensitized mice with WHI-P97 prevented the development of airway hyper-responsiveness to methacholine in a dose-dependent fashion. Furthermore, WHI-P97 inhibited the eosinophil recruitment to the airway lumen after the ovalbumin challenge in a dose-dependent fashion. Further development of WHI-P97 may therefore provide the basis for new and effective treatment as well as prevention programs for allergic asthma in clinical settings.

Role of mast cell leukotrienes in neutrophil recruitment and bacterial clearance in infectious peritonitis

Stimulated mast cells release a variety of chemotactic factors such as tumor necrosis factor alpha (TNF-alpha) and leukotriene B4. Recent studies have shown that mast cell-derived TNF-alpha plays a critical role in host defense against Gram negative bacterial infections by the recruitment of neutrophils to the sites of infection. In the present study, we sought to investigate if mast cells release leukotriene (LT) B4 in response to bacteria and, if so, to establish its in vivo relevance. We show that mast cells release significant amounts of LTB4 and LTC4 in response to exposure to FimH-expressing type 1 fimbriated Escherichia coli in vitro. To test the functional significance of mast cell-derived LTs during an E. coli infection in vivo, we examined the effect of a LT-synthesis inhibitor, A-63162, on bacterial clearance and neutrophil influx in an infectious peritonitis model in mast cell-deficient mice (WBB6F1-W/WV) and their normal congenic control (WBB6F1-+/+) mice. Our results show that a treatment with A-63162 reduced neutrophil influx and bacterial clearance in the peritoneal cavities of mast cell-sufficient but not -deficient mice. Thus, mast cell-derived LTs contribute to host defense by mediating early neutrophil influx and bacterial clearance at sites of infection.

Coordinate expression of secretory phospholipase A(2) and cyclooxygenase-2 in activated human keratinocytes

PGE(2) levels are altered in human epidermis after in vivo wounding; however, mechanisms modulating PGE(2) production in activated keratinocytes are unclear. In previous studies, we showed that PGE(2) is a growth-promoting autacoid in human primary keratinocyte cultures, and its production is modulated by plating density, suggesting that regulated PGE(2) synthesis is an important component of wound healing. Here, we examine the role of phospholipase A(2) (PLA(2)) and cyclooxygenase (COX) enzymes in modulation of PGE(2) production. We report that the increased PGE(2) production that occurs in keratinocytes grown in nonconfluent conditions is also observed after in vitro wounding, indicating that similar mechanisms are involved. This increase was associated with coordinate upregulation of both COX-2 and secretory PLA(2) (sPLA(2)) proteins. Increased sPLA(2) activity was also observed. By RT-PCR, we identified the presence of type IIA and type V sPLA(2), along with the M-type sPLA(2) receptor. Thus the coordinate expression of sPLA(2) and COX-2 may be responsible for the increased prostaglandin synthesis in activated keratinocytes during wound repair.

Histamine as an autocrine regulator of leukemic cell proliferation

We examined leukemic lymphocyte precursors from ALL patients as well as immortalized ALL cell lines for cytoplasmic histamine expression. The histamine levels ranged from 10.8 pg/10(6) cells to 82.2 pg/10(6) cells in ALL cell lines (N=4) and from 12.5 pg/10(6) cells to 1235.4 pg/10(6) cells for primary leukemic cells from ALL patients (N=13). The presence of histamine in the cytoplasm of these ALL cells was also confirmed by immunostaining using a polyclonal rabbit anti-histamine antibody. Notably, the histamine receptor blocker diphenhydramine inhibited the clonogenic growth of ALL cells by >90% prompting the hypothesis that histamine may be an autocrine regulator of ALL cell proliferation. Our study suggests that histamine receptor blockers may therefore be useful for the treatment of therapy-refractory ALL.

Targeting Janus kinase 3 in mast cells prevents immediate hypersensitivity reactions and anaphylaxis

Janus kinase 3 (JAK3), a member of the Janus family protein-tyrosine kinases, is expressed in mast cells, and its enzymatic activity is enhanced by IgE receptor/FcepsilonRI cross-linking. Selective inhibition of JAK3 in mast cells with 4-(4'-hydroxylphenyl)-amino-6, 7-dimethoxyquinazoline) (WHI-P131) blocked the phospholipase C activation, calcium mobilization, and activation of microtubule-associated protein kinase after lgE receptor/FcepsilonRI cross-linking. Treatment of IgE-sensitized rodent as well as human mast cells with WHI-P131 effectively inhibited the activation-associated morphological changes, degranulation, and proinflammatory mediator release after specific antigen challenge without affecting the functional integrity of the distal secretory machinery. In vivo administration of the JAK3 inhibitor WHI-P131 prevented mast cell degranulation and development of cutaneous as well as systemic fatal anaphylaxis in mice at nontoxic dose levels. Thus, JAK3 plays a pivotal role in IgE receptor/FcepsilonRI-mediated mast cell responses, and targeting JAK3 with a specific inhibitor, such as WHI-P131, may provide the basis for new and effective treatment as well as prevention programs for mast cell-mediated allergic reactions.

The mast cell tumor necrosis factor alpha response to FimH-expressing Escherichia coli is mediated by the glycosylphosphatidylinositol-anchored molecule CD48

Mast cells are well known for their harmful role in IgE-mediated hypersensitivity reactions, but their physiological role remains a mystery. Several recent studies have reported that mast cells play a critical role in innate immunity in mice by releasing tumor necrosis factor alpha (TNF-alpha) to recruit neutrophils to sites of enterobacterial infection. In some cases, the mast cell TNF-alpha response was triggered when these cells directly bound FimH on the surface of Escherichia coli. We have identified CD48, a glycosylphosphatidylinositol-anchored molecule, to be the complementary FimH-binding moiety in rodent mast cell membrane fractions. We showed that (i) pretreatment of mast cell membranes with antibodies to CD48 or phospholipase C inhibited binding of FimH+ E. coli, (ii) FimH+ E. coli but not a FimH- derivative bound isolated CD48 in a mannose-inhibitable manner, (iii) binding of FimH+ bacteria to Chinese hamster ovary (CHO) cells was markedly increased when these cells were transfected with CD48 cDNA, and (iv) antibodies to CD48 specifically blocked the mast cell TNF-alpha response to FimH+ E. coli. Thus, CD48 is a functionally relevant microbial receptor on mast cells that plays a role in triggering inflammation.

Quantitative high-performance liquid chromatographic method for pharmacokinetic studies of the potent mast cell inhibitor 4-(4'-hydroxyphenyl)amino-6,7-dimethoxyquinazoline (WHI-P131)

The novel quinazoline derivative 4-(4'-hydroxyphenyl)amino-6,7-dimethoxyquinazoline (WHI-P131) has recently been identified as a potent mast cell inhibitor capable of preventing IgE/antigen induced cutaneous as well as systemic fatal anaphylaxis in mice. Here we describe a sensitive high-performance liquid chromatography (HPLC)-based quantitative detection method for measurement of WHI-P131 levels in plasma as well as in target mast cells. The average extraction recovery for WHI-P131 was 88.4% for plasma and 75.7% for RBL-2H3 mast cell lysates. Good linearity (r>0.999) was observed throughout the concentration range of 0.1-20 microM in plasma and 0.01-5 nmol in 5 x 10(6) cells (0.5-238 microM per cell) for WHI-P131. Intra- and inter-assay variabilities were <7% and the lowest detection limit of WHI-P131 was 0.05 microM in plasma and 0.005 nmol in 5 million cells, respectively, at a signal-to-noise ratio of approximately 2. The practical utility of this new HPLC method was confirmed in a pilot pharmacokinetic study in BALB/c mice as well as in a cellular drug uptake and disposition study in RBL-2H3 mast cells. After intraperitoneal administration of a non-toxic 40 mg/kg bolus dose of WHI-P131, the estimated maximum plasma concentration was 92.7 microM, which is approximately 1-log higher than the effective in vitro mast cell inhibitory concentrations of WHI-P131. The drug absorption was rapid with an absorption half-life of only 2.9 min and the estimated time to reach the maximum plasma concentration was 8.3 min. WHI-P131 was cleared with an apparent systemic clearance rate of 2586 ml/h/kg and an elimination half-life of 1.8 h. An intracellular exposure level (AUC) of 55 microM x h was obtained after in vitro treatment of RBL-2H3 mast cells with WHI-P131 at a 33.6 microM final concentration in culture medium. The availability of the described quantitative HPLC detection method for WHI-P131 provides the basis for further development of WHI-P131 as an anti-allergic drug through detailed pharmacodynamic studies in preclinical animal models.

Genetic and biochemical evidence for a critical role of Janus kinase (JAK)-3 in mast cell-mediated type I hypersensitivity reactions

We investigated the role of JAK3 in IgE receptor/FcepsilonRI-mediated mast cell responses. IgE/antigen induced degranulation and mediator release were substantially reduced with Jak3-/- mast cells from JAK3-null mice that were generated by targeted disruption of Jak3 gene in embryonic stem cells. Further, treatment of mast cells with 3'bromo-4'-hydroxylphenyl)-amino-6,7-dimethoxyquinazoline (WHI-P154), a potent inhibitor of JAK3, inhibited degranulation and proinflammatory mediator release after IgE receptor/ FcepsilonRI crosslinking. Thus, JAK3 plays a pivotal role in IgE receptor/ FcepsilonRI-mediated mast cell responses and targeting JAK3 may provide the basis for new and effective treatment as well as prevention programs for mast cell-mediated allergic reactions.

Pharmacokinetics and biologic activity of the novel mast cell inhibitor, 4-(3-hydroxyphenyl)-amino-6,7-dimethoxyquinazoline in mice

PURPOSE

The purpose of the present study was to examine the pharmacodynamic and pharmacokinetic features of the novel mast cell inhibitor 4-(3'-Hydroxyphenyl)-amino-6,7-dimethoxyquinazoline (WHI-P180) in mice.

METHODS

A high performance liquid chromatography (HPLC)-based quantitative detection method was used to measure plasma WHI-P180 levels in mice. The plasma concentration-time data was fit to a single compartment pharmacokinetic model by using the WinNonlin program to calculate the pharmacokinetic parameters. A cutaneous anaphylaxis model was used to examine the pharmacodynamic effects of WHI-P180 on anaphylaxis-associated vascular hyperpermeability.

RESULTS

The elimination half-life of WHI-P180 in CD-1 mice (BALB/ c mice) following i.v., i.p., or p.o. administration was less than 10 min. Systemic clearance of WHI-P180 was 6742 mL/h/kg in CD-I mice and 8188 mL/h/kg in BALB/c mice. Notably, WHI-P180, when administered in two consecutive nontoxic i.p. bolus doses of 25 mg/kg, inhibited IgE/antigen-induced vascular hyperpermeability in a well-characterized murine model of passive cutaneous anaphylaxis.

CONCLUSIONS

WHI-P180 is an active inhibitor of IgE-mediated mast cell responses in vitro and in vivo. Further preclinical characterization of WHI-P180 may improve the efficacy of WHI-P180 in vivo and provide the basis for design of effective treatment and prevention programs for mast cell mediated allergic reactions.

Clinical implications of mast cell-bacteria interaction

Mast cells are traditionally known for mediating allergic reactions. In addition, these cells have been implicated in the pathogenesis of a variety of clinical conditions such as atopic and contact dermatitis, bullous pemphigoid, fibrotic lung disease, neurofibromatosis, psoriasis, scleroderma, rheumatoid arthritis, interstitial cystitis, ulcerative colitis, and Crohn's disease, but their role in host defense was an enigma until recently. Owing to the strategic location of mast cells at the host environment interface, their role in bacterial infections has been studied by a number of investigators. Latest reports show that mast cells have an ability to modulate the host's innate immune response to infectious agents. This review discusses the clinical implications of mast cell-bacteria interactions.

Growth regulation of primary human keratinocytes by prostaglandin E receptor EP2 and EP3 subtypes

We examined the contribution of specific EP receptors in regulating cell growth. By RT-PCR and northern hybridization, adult human keratinocytes express mRNA for three PGE2 receptor subtypes associated with cAMP signaling (EP2, EP3, and small amounts of EP4). In actively growing, non-confluent primary keratinocyte cultures, the EP2 and EP4 selective agonists, 11-deoxy PGE1 and 1-OH PGE1, caused complete reversal of indomethacin-induced growth inhibition. The EP3/EP2 agonist (misoprostol), and the EP1/EP2 agonist (17-phenyl trinor PGE2), showed less activity. Similar results were obtained with agonist-induced cAMP formation. The ability of exogenous dibutyryl cAMP to completely reverse indomethacin-induced growth inhibition support the conclusion that growth stimulation occurs via an EP2 and/or EP4 receptor-adenylyl cyclase coupled response. In contrast, activation of EP3 receptors by sulprostone, which is virtually devoid of agonist activity at EP2 or EP4 receptors, inhibited bromodeoxyuridine uptake in indomethacin-treated cells up to 30%. Although human EP3 receptor variants have been shown in other cell types to markedly inhibit cAMP formation via a pertussis toxin sensitive mechanisms, EP3 receptor activation and presumably growth inhibition was independent of adenylyl cyclase, suggesting activation of other signaling pathways.

Survival of FimH-expressing enterobacteria in macrophages relies on glycolipid traffic

Strains of Escherichia coli persist within the human gut as normal commensals, but are frequent pathogens and can cause recurrent infection. Here we show that, in contrast to E. coli subjected to opsonic interactions stimulated by the host's immune response, E. coli that bind to the macrophage surface exclusively through the bacterial lectin FimH can survive inside the cell following phagocytosis. This viability is largely due to the attenuation of intracellular free-radical release and of phagosome acidification during FimH-mediated internalization, both of which are triggered by antibody-mediated internalization. This different processing of non-opsonized bacteria is supported by morphological evidence of tight-fitting phagosomes compared with looser, antibody-mediated phagosomes. We propose that non-opsonized FimH-expressing E. coli co-opt internalization of lipid-rich microdomains following binding to the FimH receptor, the glycosylphosphatidylinositol-linked protein CD48, because (1) the sterol-binding agents filipin, nystatin and methyl beta-cyclodextrin specifically block FimH-mediated internalization; (2) CD48 and the protein caveolin both accumulate on macrophage membranes surrounding bacteria; and (3) antibodies against CD48 inhibit FimH-mediated internalization. Our findings bring the traditionally extracellular E. coli into the realm of opportunistic intracellular parasitism and suggest how opportunistic infections with FimH-expressing enterobacteria could occur in a setting deprived of opsonizing antibodies.

Localization of a domain in the FimH adhesin of Escherichia coli type 1 fimbriae capable of receptor recognition and use of a domain-specific antibody to confer protection against experimental urinary tract infection

The FimH subunit of type 1-fimbriated Escherichia coli has been implicated as an important determinant of bacterial adherence and colonization of the urinary tract. Here, we sought to localize the functionally important domain(s) within the FimH molecule and to determine if antibodies against this domain would block adherence of type 1-fimbriated E. coli to the bladder mucosa in situ and in vivo in an established mouse model of cystitis. We generated translational fusion proteins of disparate regions of the FimH molecule with an affinity tag MalE, and tested each of the fusion products in vitro for functional activity. The minimum region responsible for binding mouse bladder epithelial cells and a soluble mannoprotein, horseradish peroxidase, was contained within residues 1-100 of the FimH molecule. We validated and extended these findings by demonstrating that antibodies directed at the putative binding region of FimH or at synthetic peptides corresponding to epitopes within the binding domain could specifically block type 1 fimbriae-mediated bacterial adherence to bladder epithelial cells in situ and yeast cells in vitro. Next, we compared the ability of mice passively immunized intraperitoneally with antisera raised against residues 1-25 and 253-264 of FimH or 1-13 of FimA to resist bladder colonization in vivo after intravesicular challenge with type 1-fimbriated E. coli. Only the antibody directed at the putative binding region of FimH (anti- s-FimH1-25) significantly reduced E. coli bladder infections in the experimental mouse model of urinary tract infections. Similar results were obtained when the mice were actively immunized with synthetic peptides corresponding to residues 1-25 and 253-264 of FimH or 1-13 of FimA. The mechanism of protection was attributed, at least in part, to inhibition of bacterial adherence to the bladder surface by s-FimH1-25-specific antibody molecules that had filtered through the kidneys into the urine. The level of FimH antibodies entering the bladder from the circulatory system of the immunized mice was found to be markedly enhanced upon bacterial challenge. The potential broad spectrum activity of the protective FimH antibody was indicated from its serologic cross-reactivity with various urinary tract bacterial isolates bearing type 1 fimbriae. These findings could be relevant in the design of an efficacious and broadly reactive FimH vaccine against urinary tract infections.

Control of mast-cell 5-lipoxygenase

Leukotrienes (LTs) from mast cells make important contributions to early events in inflammation. Therefore, the control of their 5-lipoxygenase was studied. We observed that culture conditions can significantly alter LT synthesis and intracellular 5-lipoxygenase levels. Challenge of mast cells with calcium ionophore A23187 and immunoglobin E (IgE)/antigen had different effects. The calcium ionophore caused continuous LT formation that was accompanied by the translocation of the enzyme to membranes as well as substantial loss of activity. In contrast, with receptor-mediated stimulation, IgE/antigen, enzyme inactivation was insignificant, and membrane binding and LT synthesis were transient. Addition of a calcium chelator stopped ionophore-induced LT production and inactivation of the 5-lipoxygenase and reversed its membrane association. Therefore, receptor-mediated activation of 5-lipoxygenase differs from that by calcium ionophore. The data also indicate that calcium regulates the membrane binding and dissociation of the 5-lipoxygenase. However, with excessively high calcium concentrations activity is lost.

Mast cells as modulators of host defense in the lung

Mast cells display a distinct spatial distribution in the lung where they are found preferentially in intraepithelial locations or in deeper tissue around blood vessels, bronchioles and mucus secreting glands. Yet the physiological role of these granule-laden cells is unknown. There are now intriguing signs that their distinctive distribution together with their intrinsic capacity to release large amounts of inflammatory mediators serve a critical role in immune surveillance. Mast cells have now been shown to be capable of recognizing and aggressively reacting to a wide range of bacteria. The mast cell responses involve ingesting and killing of adherent bacteria, in a manner not unlike that of traditional phagocytic cells. Concomitant with this endocytic activity, a large variety of potent inflammatory mediators are released by the mast cell. One such mast cell-derived mediator, TNF-alpha, was recently shown to be a critical signal for initiating neutrophil influx to sites of bacterial infection in the lung as well as the peritoneum of mice. This capacity of mast cells to recruit neutrophils, together with its recently reported participation in processing and presenting bacterial antigens to immune cells and in mediating proliferation of epithelial cells and mucosal mucus secretion, indicate that mast cells have an extraordinary ability to modulate the innate as well as adaptive immune responses to infectious microorganisms.

Mast cell modulation of neutrophil influx and bacterial clearance at sites of infection through TNF-alpha

Although mast cells have been implicated in a variety of inflammatory conditions including immediate hypersensitivity and interstitial cystitis, their physiological role in the body is unknown. We investigated the role of mast cells in host defence against bacterial infections using a well characterized mast-cell-deficiency mouse model. We report here that mast cells, which are selectively located at portals of bacterial entry, are important to host defence. Mast-cell-deficient WBB6F1-W/Wv mice (W/Wv) were up to 20-fold less efficient in clearing enterobacteria than control WBB6F1 +/+ (+/+) mice or mast-cell-reconstituted W/Wv (W/Wv+MC) mice. With higher bacteria inocula, only W/Wv mice died (80%). The limited bacterial clearance in W/Wv mice directly correlated with impaired neutrophil influx. The mast-cell chemoattractant TNF-alpha was implicated in the neutrophil response because TNF-alpha was locally released only in +/+ and W/Wv+MC mice, TNF-alpha-specific antibodies blocked over 70% of the neutrophil influx, and purified mast cells released TNF-alpha upon incubation with bacteria. Additionally, the type-1 fimbrial subunit, FimH, was the necessary enterobacterial component for mast-cell activation and neutrophil influx because an isogenic FimH- mutant evoked a limited neutrophil response in +/+ mice compared to wild-type bacteria.

Histamine in human epidermal cells is induced by ultraviolet light injury

Human epidermal cell cultures were examined to determine whether they were capable of histamine release. Results of these studies indicated that keratinocytes contain and release significant amounts of histamine. In the skin of some individuals, histamine content was induced after ultraviolet B light injury, and 40% of subjects demonstrated high basal histamine levels. Mass spectrometric analysis of cell supernatants showed that the histamine was released into the extracellular environment. Such release may contribute to common itching or intensify the inflammatory response in vivo.

Mast cells process bacterial Ags through a phagocytic route for class I MHC presentation to T cells

The pivotal role of mast cells in allergic reactions and inflammatory processes is well established and recent studies have suggested that mast cells may also have a role in specific immune responses. Because mast cells have been shown to phagocytose and kill enterobacteria, we wished to determine whether they could also process bacterial Ags for presentation to T cells. Using a model system in which a well-characterized T cell epitope is expressed within bacteria as a fusion protein, we demonstrate in this paper that mast cells are indeed capable of processing bacterial Ags for presentation through class I MHC molecules to T cell hybridomas after phagocytic uptake of live bacteria. Processing occurs from a number of Gram-negative enterobacteria including Salmonella typhimurium and Escherichia coli. Parallel assays show that processing of the model Ag from enterobacteria by mast cells is similar in efficiency to processing by peritoneal macrophages. Consistent with earlier observations demonstrating a function of the bacterial fimbrial protein FimH in promoting bacterial binding to mast cells, the magnitude of the Ag processing response of E. coli is influenced by bacterial expression of FimH. Taken together, these observations extend the range of cell types capable of the phagocytic pathway of Ag processing and suggest that mast cells may have a previously unrecognized role in the induction of specific immune responses to bacteria.

Mast cells process bacterial Ags through a phagocytic route for class I MHC presentation to T cells

The pivotal role of mast cells in allergic reactions and inflammatory processes is well established and recent studies have suggested that mast cells may also have a role in specific immune responses. Because mast cells have been shown to phagocytose and kill enterobacteria, we wished to determine whether they could also process bacterial Ags for presentation to T cells. Using a model system in which a well-characterized T cell epitope is expressed within bacteria as a fusion protein, we demonstrate in this paper that mast cells are indeed capable of processing bacterial Ags for presentation through class I MHC molecules to T cell hybridomas after phagocytic uptake of live bacteria. Processing occurs from a number of Gram-negative enterobacteria including Salmonella typhimurium and Escherichia coli. Parallel assays show that processing of the model Ag from enterobacteria by mast cells is similar in efficiency to processing by peritoneal macrophages. Consistent with earlier observations demonstrating a function of the bacterial fimbrial protein FimH in promoting bacterial binding to mast cells, the magnitude of the Ag processing response of E. coli is influenced by bacterial expression of FimH. Taken together, these observations extend the range of cell types capable of the phagocytic pathway of Ag processing and suggest that mast cells may have a previously unrecognized role in the induction of specific immune responses to bacteria.

The PapG tip adhesin of P fimbriae protects Escherichia coli from neutrophil bactericidal activity

Compared with Escherichia coli ORN103, a nonfimbriated K-12 strain, P-fimbriated E. coli ORN103/pPAP5 was found to interact poorly with human neutrophils and resist their bactericidal activity in vitro. PapG, the Gal alpha(1-->4)Gal binding moiety located at the distal end of the P fimbrial filament, appeared to be responsible for this effect because an isogenic PapG- mutant, E. coli ORN103/pPAP24, exhibited binding interactions with neutrophils that were similar to nonfimbriated E. coli ORN103. Although no direct evidence is available, the poor adherence mediated by PapG could be related to its electrostatic properties because the isolated PapG protein had a pI of 5.2, which indicated that in the physiological pH range it possessed a net negative charge. Antibodies against PapG overcame the protective effect of PapG and markedly enhanced the interactions of P-fimbriated E. coli with neutrophils resulting in bacterial killing. When a P-fimbriated clinical E. coli strain or its isogenic PapG- derivative was injected into the peritoneal cavities of mice, a similar number of neutrophils was recruited to the site of injection. After 2 h, the number of P-fimbriated E. coli organisms that survived the neutrophil influx in the mouse peritoneum was approximately four times more than the number of surviving PapG- bacteria. This result demonstrates that the PapG protein, which is strategically located at the distal region of the P-fibrillum structure, protects E. coli from the bactericidal action of neutrophils.

Mast cell degranulation induced by type 1 fimbriated Escherichia coli in mice

The strategic location of mast cells at the host-environment interface and their ability to release potent mediators of inflammation have suggested that these cells may play a pivotal role in host defense against bacterial infection. The ability of the opportunistic pathogen, Escherichia coli, to induce degranulation of mast cells obtained from the mouse peritoneum was investigated. We determined that unlike a mutant derivative deficient in the FimH subunit of the fimbriae or nonfimbriated E. coli, type 1 fimbriated E. coli induced mast cell degranulation in vitro. The magnitude of mast cell degranulation was directly proportional to the number of adherent bacteria on the cell surface in the initial period of the interaction. Using a mouse model of bacterial peritonitis, we demonstrated mast cell degranulation and histamine release by type 1 fimbriated bacteria in vivo. Furthermore, beads coated with FimH but not with FimA, the major subunit of type 1 fimbriae, evoked mast cell release of histamine in vivo in amounts comparable to that elicited by type 1 fimbriated E. coli. These studies reveal that mast cells can be degranulated by interaction with type 1 fimbriated E. coli and that FimH, the mannose-binding component of the fimbriae, is a potent mast cell stimulant.

Effect of D-penicillamine on lymphocyte subsets: correlation with clinical response in rheumatoid arthritis

We studied the effects of D-penicillamine (DP) on the clinical response, immunoinflammatory parameters and the lymphocyte subsets in 46 patients with rheumatoid arthritis (RA). Patients were evaluated before the start of the drug and then at 3 and 9 months during the follow up. 38 of 46 (82.6%) patients could continue DP treatment for over 9 months, while in 8 the drug was withdrawn due to adverse effects. Improvement in the various disease activity indices of more than 50% (responders) was seen in 25 of 38 (65.8%) patients. Responders showed a significant decrease in the serum IgA and IgM at 9 months, and in IgM only at 3 months. The serum levels of C3 and C4 did not show any significant change. Serum levels of C-reactive protein and rheumatoid factor (RF) showed a significant decrease at 3 and 9 months. A significant decrease in CD3+ and CD4+ lymphocytes along with a fall in CD4+/CD8+ lymphocyte ratio was also seen in responders at 3 and 9 months, compared to the baseline. Our results suggest that DP may have immunomodulatory action in RA.

Mast cell phagocytosis of FimH-expressing enterobacteria

Most studies of mast cells have been directed at their role in the pathophysiology of IgE-mediated allergic reactions with little recognition of their participation in bacterial infections. We report that mast cells can specifically bind FimH, a mannose-binding subunit on type 1 fimbriae expressed by Escherichia coli and other enterobacteria. This interaction triggers mast cell phagocytosis and killing of the bacteria within vacuoles and through the release of superoxide anions. Also, in view of the fact that mast cells have the capacity to release inflammatory mediators and are particularly abundant in the skin, mucosal surfaces, and around blood vessels, we suggest that these cells play an important role in host defense against microbial infection.

Mast cell phagocytosis of FimH-expressing enterobacteria

Most studies of mast cells have been directed at their role in the pathophysiology of IgE-mediated allergic reactions with little recognition of their participation in bacterial infections. We report that mast cells can specifically bind FimH, a mannose-binding subunit on type 1 fimbriae expressed by Escherichia coli and other enterobacteria. This interaction triggers mast cell phagocytosis and killing of the bacteria within vacuoles and through the release of superoxide anions. Also, in view of the fact that mast cells have the capacity to release inflammatory mediators and are particularly abundant in the skin, mucosal surfaces, and around blood vessels, we suggest that these cells play an important role in host defense against microbial infection.

Effect of culture conditions on mast cell eicosanoid synthesis

When mast cells are grown in culture from mouse bone marrow cells, some cells are in suspension and some attach. The cells in suspension released leukotrienes and thromboxane when stimulated. Removal from the attached cells increased eicosanoid formation in the suspended cells two- to six-fold. The upregulation of arachidonic acid metabolism seemed to be due to an increase in phospholipase activity. The attached cells resembled macrophages in morphology, but stained positively for mast cells and produced PGD2 an arachidonic acid metabolite which is characteristic for mast cells. The attached cells did not synthesize eicosanoids when stimulated with IgE/antigen or A23187. Addition of arachidonic acid caused cyclooxygenase product formation but not leukotrienes. No 5-lipoxygenase was detected by immunoblot analysis. Lack of eicosanoid synthesis was, therefore, due to the loss of 5-lipoxygenase and phospholipase activity, while the cyclooxygenase was preserved. These experiments demonstrate that attachment of mast cells to plastic can significantly alter their eicosanoid metabolism.

Reversible translocation of 5-lipoxygenase in mast cells upon IgE/antigen stimulation

The 5-lipoxygenase catalyzes the first two steps in the metabolism of arachidonic acid to leukotrienes. It has been shown that the calcium influx into leukocytes following stimulation by A23187 activates the enzyme and causes its translocation to the membrane. Leukotrienes are formed, and then the enzyme seems to be irreversibly inactivated. In the present investigation we have compared the effect of receptor-mediated mast cell activation (IgE/antigen) and A23187 on 5-lipoxygenase activity and translocation to the membrane. In contrast to the ionophore, IgE/antigen, which initiated the formation of similar amounts of leukotrienes as A23187, caused minor inactivation of the enzyme. Immunoblot analysis demonstrated that after antigen the membrane association of the 5-lipoxygenase was reversible, while with A23187 the translocation continued during the time of observation (60 min). Addition of a calcium chelator after ionophore challenge, prevented further inactivation of the enzyme and reversed its membrane binding. The data suggest that the continuous influx of calcium with A23187 is responsible for the extensive inactivation of the 5-lipoxygenase. In contrast, during receptor-mediated stimulation the transient increase in intracellular calcium seems to conserve the enzyme activity.

Methotrexate: clinical and immunological effects in refractory rheumatoid arthritis

Thirty five patients with refractory rheumatoid arthritis were given 7.5 mg of methotrexate (Mtx) every week. Eleven patients had to discontinue treatment either because of adverse effects or unresponsiveness. Twenty four patients showed clinical response and significant improvement in ESR and they continued Mtx for a mean of 25.24 months. Seven patients achieved clinical remission as defined by ARA criteria. Immunological parameeters including IgG, IgM, IgA, lymphocyte subsets (CD3+, CD4+, CD8+ and B), C3 and C4 however, did not show any change during this treatment in any of the groups upto 6 months. There was a significant fall in the erythrocyte sedimentation rate (ESR), c-reactive protein (CRP) and rheumatoid factor (RF) levels in responders only.

Intermittent intravenous pulse cyclophosphamide treatment in systemic lupus erythematosus

To determine the efficacy and safety of intermittent intravenous pulse cyclophosphamide in patients of severe systemic lupus erythematosus (SLE), 50 patients having severe/refractory lupus nephritis, vasculitis or neuropsychiatric manifestations were treated with 3 weekly pulses of cyclophosphamide for 6 such pulses. This treatment was found to be associated with significant and sustained improvement during a 2 yr follow up with respect to the mean renal activity score, individual renal parameters (proteinuria, erythrocyturia, and serum creatinine levels), focal neurological manifestations, vasculitic lesions, antinuclear antibody titers, complement component C3, anti-dsDNA antibodies levels and ESR. There was a sustained decrease in the overall mean disease activity score, and the mean daily dose of prednisolone (pretreatment 32.62 mg daily to 3.75 mg daily after 24 months). There was a significant decline in the percentage and absolute B cell count after 7, 14 and 21 days of this treatment. Effect on other lymphocyte subsets (CD3+, CD4+ and CD8+) was not marked. Pulse cyclophosphamide could therefore be an effective and less toxic form of treatment in patients with SLE having severe lupus nephritis, focal neurological lesions or vasculitis.

Effect of high dose intravenous pulse dexamethasone on lymphocyte phenotypes

The lymphocyte phenotypes were enumerated in 10 patients with collagen diseases at 0 h, 4 h, 24 h and 7 days after a megadose (100 mg) iv pulse dexamethasone. A significant decrease in CD3 (from a mean of 2324.3/mm3 to 705.9/mm3) and CD4 (from a mean of 1642.6 to 317.6/mm3) cells was observed at 4 h, which recovered partially by 24 h (186.7 and 1226.3/mm3 respectively) and completely at 7 days (2496.1 and 1838.4/mm3). A transient decrease in CD8 cells at 4 h was also observed. There was no significant effect on B cells.

Role of circulating immune complexes in the immunopathogenesis of silicosis

The sera of 19 silica-dust-exposed subjects and of an equal number of age-, sex- and socioeconomic-strata-matched controls were analysed for antinuclear factor, rheumatoid factor, C-reactive protein, immunoglobulins G, M, A, and complement C3 and C4. Circulating immune complexes were also precipitated in all subjects and their immunoglobulin and complement C3 and C4 were estimated. Silica-exposed subjects were divided into two groups depending upon the radiological findings and it is suggested that IgA plays an important role in the immunopathogenesis of the disease and that lung changes could be due to the immune-complex-mediated mechanisms utilizing an alternative complement pathway.