Establishment and characterization of hybrid rat mast cells

Exposure to tobacco-derived materials induces overproduction of secreted proteinases in mast cells

Mast cells reside at interfaces with the environment, including the mucosa of the respiratory and gastrointestinal tracts. This localization exposes mast cells to inhaled, or ingested, environmental challenges. In the airways of smokers, resident immune cells will be in contact with the condensed components of cigarette smoke. Mast cells are of particular interest due to their ability to promote airway remodeling and mucus hypersecretion. Clinical data show increased levels of mast cell-secreted tryptase and increased numbers of degranulated mast cells in the lavage and bronchial tissue of smokers. Since mast cell-secreted proteinases (MCPTs), including tryptases, contribute to pathological airway remodeling, we investigated the relationship between mast cell proteinases and smoke exposure. We exposed a mast cell line to cigarette smoke condensate (CSC). We show that CSC exposure increases MCPT levels in mast cells using an assay for tryptase-type MCPT activity. We hypothesized that this increase in MCPT activity reflects a CSC-induced increase in the cytosolic pool of proteinase molecules, via stimulation of MCPT transcription. Transcript array data suggested that mRNA changes in response to CSC were limited in number and peaked after 3 h of CSC exposure. However, we noted marked transcriptional regulation of several MCPT genes. CSC-induced changes in the mRNA levels for MCPTs were confirmed using quantitative RT-PCR. Taken together, our data suggest that chronic exposure to cigarette smoke up-regulates MCPT levels in mast cells at both the protein and the mRNA level. We suggest that the pathological airway remodeling that has been described in clinical studies of smoke inhalation may be attributable to MCPT overproduction in vivo.

Trichinella spiralis: Stimulation of mast cells by TSL-1 antigens trigger cytokine mRNA expression and release of IL-4 and TNF through an Ig-independent pathway

Previous in vitro studies have demonstrated that mast cells (MC) can be directly activated by Trichinella spiralis larvae 1 (TSL-1) antigens. To characterize even more this activation of MC and their possible role on induction and regulation of the Type 2 response generated against T. spiralis infection, we studied the interaction between a hybrid rat MC line (HRMC), murine bone marrow MC (mBMMC), and TSL-1 antigens. Immunofluorescence staining and flow cytometry analysis showed that TSL-1 antigens bound to the surface of HRMC cells, resulting in the transcriptional induction and in the release of TNF and IL-4. Besides, an increase of IL-4 intracellular expression was also observed in mBMMC. This suggests that MC may play an important role in the early immune response against T. spiralis and may be a source of cytokines, that regulate the final onset of the immune mechanisms which determine the course of the infection.

Effects of cannabinoid receptor agonists on immunologically induced histamine release from rat peritoneal mast cells

Immunologic activation of mast cells through the cross-linking of high affinity IgE receptors results in the release of inflammatory mediators which are important in the pathogenesis of allergic reactions. Early studies investigating the effects of palmitoylethanolamide on animal models of inflammation and on rat mast cells led to the hypothesis that endogenous cannabinoids might act as local autacoids which suppressed inflammation by reducing the activation of mast cells. However, more recent studies produced contradicting results. In order to evaluate if cannabinoid receptors are present in mast cells, we studied the effects of endocannabinoids (anandamide and palmitoylethanolamide) and synthetic cannabimimetics (CP 55,940, WIN 55,212-2 and HU-210) on histamine release from rat peritoneal mast cells. When incubated with mast cells alone, only anandamide could induce significant level of histamine release at concentrations higher than 10(-6) M. When mast cells were activated with anti-IgE, the histamine release induced was not affected by anandamide, palmitoylethanolamide and CP 55,940. In contrast, both WIN 55,212-2 and HU-210 enhanced anti-IgE-induced histamine release at 10(-5) M and preincubation did not increase the potency. The histamine releasing action of anandamide and the enhancing effects of WIN 55,212-2 and HU-210 on anti-IgE-induced histamine release were not reduced by the cannabinoid receptor antagonists, AM 281 and AM 630. In conclusion, the present study does not support the hypothesis that cannabinoids suppress mast cell activation. Instead, some of the cannabinoid receptor-directed ligands tested enhanced mast cell activation. However, the high concentrations required and the failure of cannabinoid receptor antagonists to reverse such effects also question the existence of functional cannabinoid receptors in mast cells.

cDNA cloning, expression, mutagenesis, intracellular localization, and gene chromosomal assignment of mouse 5-lipoxygenase

5-Lipoxygenase of mouse macrophages and bone marrow-derived mast cells (BMMC) was investigated. Indirect immunocytofluorescence combined with confocal microscopy provided evidence for distinct intracellular expression patterns and trafficking of 5-lipoxygenase upon cellular activation. In resting BMMC, 5-lipoxygenase was found within the nucleus co-localizing with the nuclear stain Yo-Pro-1. When BMMC were IgE/antigen-activated the 5-lipoxygenase immunofluorescence pattern was changed from nuclear to perinuclear. The absence of divalent cations in the incubation medium, or calcium ionophore A23187 challenge, altered the predominantly nuclear expression pattern to new sites both cytosolic and intranuclear. The cDNA for murine macrophage 5-lipoxygenase was cloned by the polymerase chain reaction and would predict a 674 amino acid protein. Using control cells obtained from 5-lipoxygenase-deficient mice it was determined that a single isoform accounts for both soluble and membrane-bound and nuclear and cytosolic-localized enzyme in macrophages and BMMC. A mutation at amino acid 672 (Val-->Met) introduced serendipitously during the cloning process was found to completely abolish 5-lipoxygenase enzyme activity when the enzyme was expressed in human embryonic kidney 293 cells. This subtle change is proposed to affect the ability of the COOH-terminal isoleucine to coordinate the essential non-heme iron atom. In macrophages and BMMC obtained from 5-lipoxygenase-deficient mice, compensatory changes in expression of genes involved in the biosynthesis of leukotriene B4 were investigated. 5-Lipoxygenase-activating protein expression was reduced by 50%, while leukotriene A4 hydrolase expression was unaltered. The 5-lipoxygenase gene was mapped to the central region of mouse chromosome 6 in a region that shares homology with human chromosome 10 by interspecific backcross analysis. These studies provide a global picture of the murine 5-lipoxygenase system and raise questions about the role of 5-lipoxygenase and leukotrienes within the nucleus.

Giant cell formation in Hodgkin's disease

The identity of Reed-Sternberg cells in Hodgkin's disease has remained an unresolved issue, though many studies have addressed this question. Giant cells are usually formed either by endomitosis without cytoplasmic division or by cell fusion through cytokines or viruses. Growing evidence associates Epstein-Barr virus (EBV) with Hodgkin's disease, a major issue being whether EBV is a passenger virus or has an aetiological role. This communication describes experimental conditions enabling observation of giant cell cytogenesis from peripheral blood mononuclear cells in culture. Mononuclear cells were isolated from autologous peripheral blood and cocultured with a single-cell suspension obtained from Hodgkin's lymph nodes in a culture chamber where the two cell populations are isolated by a microporous membrane that allows only cytokines and viruses to pass through. Under these experimental conditions, giant cells are formed in the peripheral blood mononuclear cell fraction; some of them appear morphologically indistinguishable from Reed-Sternberg cells and their mononuclear variant, while others much resemble Langhans giant cells. Some of these giant cells are positive for EBV DNA by in situ hybridization. These results suggest that an EBV-dependent biological activity is responsible for giant cell cytogenesis originating from lymphocytes and monocytes, induced either by EBV and/or cytokines.

The N-linked oligosaccharides of the Fc epsilon receptors of rat basophilic leukemia cells

This study was undertaken to investigate the nature and microheterogeneity of the carbohydrate moiety of the Fc epsilon receptors of RBL-CA10 and RBL-CA10.7 cells. Treatment using the glycosylation processing inhibitors, castanospermine (CN), 1-deoxymannojirimycin (DMJ), and swainsonine (SW) resulted in a decrease of the relative molecular mass (M(r)) of both the alpha-chain of the high affinity receptor for IgE, Fc epsilon RI(alpha), and the low affinity receptor for IgE, Fc epsilon RL. Exposure to DMJ had the greatest effect on the M(r), while CN seemed to lead to a decreased cell surface expression of Fc epsilon RI. Both receptors are largely resistant to endoglycosidase H as their M(r) decreased only by approximately 2 kDa. These results suggest that both receptors are composed primarily of complex oligosaccharides with a single high mannose, N-glycosylated site. Both Fc epsilon receptors become endoglycosidase H sensitive if first exposed to DMJ which indicates that the carbohydrate composition is indeed altered by this processing inhibitor presumably by blocking the formation of complex structures. When the Fc epsilon receptors were reduced and hydrolyzed by N-glycanase, the M(r) values for Fc epsilon RI(alpha) and Fc epsilon RL decreased to approximately 28 and 34-38 kDa respectively. In the case of Fc epsilon RI(alpha), this implies the presence of only a small amount of O-linked oligosaccharides.