Mast cells and sphingosine-1-phosphate underlie prelesional remodeling in a mouse model of eczema.

BACKGROUND: Atopic dermatitis (AD) is a chronic skin inflammation that affects children and adults worldwide, but its pathogenesis remains ill-understood. METHODS: We show that a single application of OVA to mouse skin initiates remodeling and cellular infiltration of the hypodermis measured by a newly developed computer-aided method. RESULTS: Importantly, we demonstrate that skin mast cell (MC) activation and local sphingosine-1-phosphate (S1P) are significantly augmented after OVA treatment in mice. Deficiency in sphingosine kinase (SphK)1, the S1P-producing enzyme, or in MC, remarkably mitigates all signs of OVA-mediated remodeling and MC activation. Furthermore, skin S1P levels remain unchanged in MC-deficient mice exposed to OVA. LPS-free OVA does not recapitulate any of the precursor signs of AD, supporting a triggering contribution of LPS in AD that, per se, suffice to activate local MC and elevate skin S1P. CONCLUSION: We describe MC and S1P as novel pathogenic effectors that initiate remodeling in AD prior to any skin lesions and reveal the significance of LPS in OVA used in most studies, thus mimicking natural antigen (Ag) exposure.

IL-6 attenuates apoptosis, while neither IL-6 nor IL-10 affect the numbers or protease phenotype of fetal liver-derived human mast cells.

BACKGROUND: The combination of recombinant human stem cell factor (rhSCF), rh interleukin (IL)-6 and rhIL-10 was reported to be optimal for mast cell development from cord blood progenitors and to induce chymase expression in all such mast cells earlier in their development than tryptase. OBJECTIVE: The effects of rhIL-6 and rhIL-10 in various combinations on the rhSCF-dependent development of human mast cells from fetal liver progenitors were examined in serum-free media. METHODS: Dispersed fetal liver cells were cultured in serum-free AIM-V medium with rhSCF alone, or with combinations of rhIL-6 and rhIL-10. Tryptase and chymase expression, surface Kit expression, metachromasia with toluidine blue and apoptosis were measured. RESULTS: Neither rhIL-6 nor rhIL-10 nor the two interleukins together, when included from day 0 of culture, affected the number or protease phenotype of mast cells at 1 or 3 weeks. Expression of tryptase paralleled the appearance of metachromasia and surface Kit, both of which preceded chymase expression, regardless whether a rabbit polyclonal or mouse monoclonal anti-chymase antibody preparation was used. On the other hand, rhIL-6 markedly attenuated baseline levels of apoptosis in the presence of rhSCF as well as apoptosis occurring after withdrawal of rhSCF, whereas rhIL-10 had no effect. CONCLUSION: RhIL-6 protected fetal liver-derived mast cells from apoptosis, particularly after withdrawal of rhSCF, but neither rhIL-6 nor rhIL-10 nor the combination of these interleukins affected the numbers or protease phenotype of these mast cells.

Recombinant human (rh)IL-4-mediated apoptosis and recombinant human IL-6-mediated protection of recombinant human stem cell factor-dependent human mast cells derived from cord blood mononuclear cell progenitors.

Although stem cell factor (SCF) appears to be the major growth factor for human mast cells, other factors undoubtedly play important roles in the development, survival, and function of these cells. The current study examined the effects of recombinant human (rh) IL-4 and rhIL-6 on rhSCF-dependent development and survival of human mast cells derived in vitro from cord blood progenitor cells. After 4-8 wk of culture with rhSCF and various amounts of rhIL-4, a dramatic decline in mast cell numbers was observed with rhIL-4, the EC50 being about 0.1 ng/ml. Numbers of other cell types remained high. Mast cells derived from cord blood progenitors after 7 wk of culture with rhSCF alone displayed an MCT phenotype and expressed Kit, FcepsilonRI, and IL-4R on their surface. Mast cells examined after purification by immunomagnetic sorting became apoptotic within hours after exposure to rhIL-4, a phenomenon blocked by anti-IL-4 Ab. Because rhIL-4-dependent apoptosis but not the loss of mitochondrial membrane potential was prevented by the pan-caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp-(Z-VAD)-fluoromethylketone, mitochondrial perturbation most likely preceded caspase activation. Consistent with this conclusion was the observation that both apoptosis and loss of mitochondrial membrane potential (Deltapsim) were inhibited by cyclosporin A in combination with aristolochic acid. rhIL-6 protected cord blood mast cells from rhIL-4-induced apoptosis. Thus, IL-4 can cause both maturation and apoptosis of human mast cells, the latter effect being abrogated by IL-6.

Recombinant murine (rm) interleukin (IL)-5 enhances the eosinophil peroxidase content in cells cultured in vitro compared with rmIL-3 and granulocyte-macrophage colony-stimulating factor.

We previously reported an in vitro bioassay permissive to eosinophil production from naive mouse bone marrow cells. Based on cytosmear analysis, recombinant murine (rm) interleukin (IL)-3 combined with granulocyte-macrophage colony-stimulating factor (GM-CSF) provided better quantitative cellular yields compared with rmIL-5. In the present study, we compared the eosinophil peroxidase (EPO) content obtained in both in vitro conditions using microtitration. Parallel with the EPO assay, the percentage of eosinophils present in cultures was determined by cytosmear analysis. Cells incubated with IL-5 displayed significantly higher EPO activity than those cultured in the presence of IL-3 and GM-CSF. At the end of the culture period, cells were further enriched in eosinophils as determined by centrifugation gradient. Enhanced amounts of cellular EPO were detected when cultures were performed in the presence of IL-5. With regard to the correlation between eosinophil maturation and EPO acquisition, eosinophil cells cultured with rmIL-5 expressed significantly more EPO activity than those generated in the presence of rmIL-3 and GM-CSF.

Exogenous and endogenous antigens are differentially presented by mast cells to CD4+ T lymphocytes.

In the present work, we explored the cytokine-dependent regulation of bone marrow-derived mast cell (BMMC) antigen-presenting cell (APC) function, and co-stimulation requirements, and analyzed the nature of antigens presented to T cells. We observed an up-regulation of the APC function of mast cells induced by granulocyte/macrophage-colony-stimulating factor (GM-CSF) and a complete abrogation by interferon (IFN)-gamma. Expression of co-stimulatory molecules CD80 and CD86 was suggested by the ability of mast cells to activate purified lymph node-derived T cells. Indeed, addition of the fusion protein mCTLA4-Ig strongly inhibited antigen presentation by mast cells to normal T cells and to the T cell hybridoma 3DO-54.8. The regulatory mechanisms of APC function by GM-CSF and IFN-gamma were investigated by measuring CD80 and CD86 transcripts in mast cells. GM-CSF-treated must cells showed a strong increase in the expression of both CD80 and CD86 transcripts, whereas in IFN-gamma-treated mast cells, this expression was completely abrogated. Thus, up- and down-regulation of CD80 and CD86 expression by GM-CSF and IFN-gamma is directly correlated to the APC function. In addition, we analyzed antigen presentation by mast cells of endogenous self-antigens. Mast cells failed to activate anti-I-A or anti-I-E-specific T cell hybridomas and alloreactive T cells in primary mixed lymphocyte reactions (MLR). Furthermore, mast cells did not present the mouse beta 2-microglobulin (m beta 2-m) peptide 25-40, constitutively expressed on B cells. However, mast cells, especially those treated with GM-CSF, activated an anti-m beta 2-m-specific T cell hybridoma in the presence of exogenous peptide. The minor lymphocyte-stimulating antigen-1 Mls-1a is a viral superantigen (vSAG) encoded by the the mouse mammary tumor provirus-7 (MMTV-7). Mast cells, despite a reasonable amount of major histocompatibility complex class II on the cell surface and the presence of MMTV transcripts predicted to encode the vSAG, cannot stimulate in vivo or in vitro V beta 6+ T cells specific for Mls-1a. In contrast, mast cells could present the exogenous bacterial SAG, staphylococcal enterotoxin B (SEB), to specific V beta 8+ T cells. The selective ability of mast cells to present exogenous antigens may have physiological relevance in that mast cells could participate in immune response regulatory mechanisms by discriminating self from nonself.

Activated mast cells release biological activities able to support eosinophil production from mouse hemopoietic precursors.

Mouse bone marrow cells cultured for 6 days in the presence of recombinant murine IL-3 and granulocyte-macrophage colony-stimulating factor (GM-CSF) were used as a source of precursors responsive to eosinopoietins. They were further cultured for 7 days in the presence of either a combination of recombinant cytokines or supernatants of bone marrow-derived mast cells (BMMC) activated with either immunological or nonimmunological stimuli. Cytosmears of collected cells were analyzed for eosinophil contents and allowed to demonstrate that supernatants of passively sensitized BMMC support both total cell proliferation and eosinophil production, after various periods of incubation with monoclonal rat anti-mouse IgE antibodies (the 6HD5 mAbs). In contrast, a stimulation with 100 ng/ml dinitrophenylated bovine serum albumin (DNP-BSA) did not generate supernatants displaying such bioactivities. Low doses of methyl ester of L (but not D)-leucine or of the calcium ionophore A23187 also allowed the release of eosinopoietic bioactivities. In addition, immunoreactive IL-5, GM-CSF, and IL-3 were quantified in the BMMC supernatants. These results demonstrate that activated BMMC are able to effect eosinophil production.

Presentation of soluble antigens by mast cells: upregulation by interleukin-4 and granulocyte/macrophage colony-stimulating factor and downregulation by interferon-gamma.

We recently showed that bone marrow-derived mast cells bore MHC class II molecules and could present antigens to specific T cell hybridomas. This article summarizes the effects of purified recombinant cytokines on the expression of MHC class II molecules by mast cells and on their antigen-presenting capacity. Since IL-3 is essential for mast cell growth, all the cytokines were analyzed in the presence of IL-3. IL-3 downregulated the production of Ia molecules, so that mast cells cultured in IL-3 alone had no antigen presenting ability. In contrast, IL-4 and IFN-gamma upregulated the production of MHC class II molecules, while GM-CSF had no effect. The antigen-presenting capacity of IL-4-treated mast cells was substantially enhanced by incubating these cells with GM-CSF for 2 days. GM-CSF enhanced antigen presentation only in combination with IL-4. The activation of mast cells was reversible and could not be repeated. Finally, incubation of IL-4- or IL-4/GM-CSF-treated mast cells with IFN-gamma led to almost complete inhibition of the antigen-presenting function. These findings provide new insights into the regulation of specific allergic responses.

Antigen-dependent stimulation by bone marrow-derived mast cells of MHC class II-restricted T cell hybridoma.

This paper describes a new role for mast cells as being able to present Ag to immune T cells. A mouse bone marrow-derived mast cell population obtained after 3 wk of culture in a conditioned medium has been shown to express a variety of membrane-associated Ag, including MHC class II and class I Ag, CD23, CD32, high affinity receptor for IgE, and CD4. Expression of MHC class II molecules was up-regulated upon stimulation with LPS but not with IFN-gamma and was down-regulated after exposure of mast cells to IL-3 treatment. We have demonstrated that mast cells were able to present native Ag as well as immunogenic peptides to MHC class II-restricted T cell hybridoma. The inhibition of Ag presentation after mast cells have been treated with ammonia suggests that Ag catabolism in intracytoplasmic compartment as a key step in Ag handling takes place in these cells. The MHC class II molecule is the restricting element for the presentation of OVA and the lambda repressor from bacteriophage lambda to a panel of specific T cell hybridomas, as demonstrated by the blocking effect of anti-MHC class II mAb on the Ag-presenting function. A characteristic feature of mast cells is the generation of a narrower immunogenic peptide repertoire as compared with A20 and LBB 3.4.16, a B lymphoma cell line, and a B cell hybridoma, respectively. This novel function of mast cells brings to a much closer connection inflammatory and immunologic processes and sheds new light on the biology of mast cells and particularly on the specific allergic responses.

In vivo assessment of mast cell functional alteration induced by L-leucine methyl ester, using the passive cutaneous anaphylaxis technique.

We have recently reported that in vitro, mast cells were sensitive to the action of L-leucine methyl ester (Leu-OMe), a lysosomotropic compound. We now report the in vivo effect of Leu-OMe on mast cells, qualitatively assessed by using the passive cutaneous anaphylaxis (PCA) reaction. The L- but not the D-stereoisomer of Leu-OMe (25 mM) injected together with Dactylis glomerata, pollen-specific, IgE-containing serum inhibited the PCA reaction in rat skin triggered by a subsequent challenge with the corresponding allergen. When specific IgE antibodies were injected in the rat skin 3 days after the L-Leu-OMe, subsequent challenge with the antigen displayed a recovery of the PCA reaction. Thus, an in vivo L-Leu-OMe treatment, at a concentration which did not lead to any macroscopic tissue injury, elicited either an alteration of mast cell mediator release or an inhibition of allergen-induced vasoactive mediator release through a functional deactivation and/or a depletion of mast cells.

Ultrastructural changes in mouse peritoneal mast cells in response to L-leucine methyl ester or anti-IgE.

We studied the ultrastructural features of mouse peritoneal mast cells in response to a non-immunologic lysosomotropic agent, L-leucine methyl ester (Leu-OMe), as compared to well-known immunologic stimulation mediated by anti-IgE antibodies. Total peritoneal exudate cells were collected from CBA/J mice, with mast cells representing 3 to 8% of total cells. The secretory granules in unstimulated mast cells were heterogeneous in size and shape, but intragranular material displayed a homogeneous electron-dense appearance. Stimulation with either Leu-OMe, for Leu-OMe doses lower than 1.5 mM, or anti-IgE was associated with fusion of the granule membranes with one another and with the plasma membrane, as evidenced by morphologic changes noted by electron microscopy. Ultrastructurally, electron density characterizing the granular matrix decreased to varying degrees in the granules, as did its homogeneity, even within a given mast cell. At higher Leu-OMe doses (> 1.5 mM), the effect of this lysosomotropic compound on mast cells was associated with an apparent loss of membrane and cellular integrity, suggesting high Leu-OMe dose-mediated cytotoxicity. These results show that activation induced in mouse peritoneal mast cells by Leu-OMe and anti-IgE may have distinct characteristics, as assessed by morphologically different patterns. Furthermore, high Leu-OMe doses (> 1.5 mM) induced cytotoxicity targeted toward mast cells.

Effects of L-leucine methyl ester (Leu-OMe) on mouse peritoneal mast cells: characterization of histamine release versus cytotoxicity.

L-Leucine methyl ester (Leu-OMe), a lysosomotropic compound, has been found to eliminate several lysosome-rich cellular subtypes and all natural killer cell function from peripheral blood mononuclear cells. In this report, the effect of Leu-OMe on mouse peritoneal mast cells is described. The L-Leu-OMe induced the release of histamine from mouse peritoneal mast cells in a dose-dependent manner (0.25 to 3 mM), while its D-stereoisomer had no effect. L-Leu-OMe displayed also a potent histamine release effect on purified mast cells, indicating a direct effect on mast cells. The monitoring of radioactive chromium release versus histamine release showed that both processes may be unrelated for Leu-OMe concentrations inferior to 1.5 mM. At higher doses, L-Leu-OMe, but not its D-stereoisomer, exerted a potent cytotoxic effect on mast cells. The secretory effect of Leu-OMe was temperature- and energy-dependent. Experiments performed in the absence of extracellular calcium and magnesium demonstrated that these divalent cations were not necessary for the Leu-OMe-induced histamine release, and their deprivation even involved a higher histamine release. The secretory characteristics of the Leu-OMe-induced histamine release appeared to be different from those of the IgE-induced ones. These results support the conclusion that exposure of mouse peritoneal mast cells to high doses of L-Leu-OMe results in killing of these cells, that are new targets of this lysosomotropic agent.