Background Angiogenesis and lymphangiogenesis are critical for several allergic, inflammatory, and neoplastic disorders. Mast cells infiltrate the sites of inflammation and tumors. Objective We ...sought to characterize the expression and functions of vascular endothelial growth factors (VEGFs) and their receptors (VEGFRs) in human mast cells. Methods VEGF expression was evaluated by means of RT-PCR and Western blotting in primary human lung mast cells and in the mast cell lines LAD-2 and HMC-1. Angiogenic activity of mast cell supernatants was determined by using the chick embryo chorioallantoic membrane assay. VEGFR expression was assessed by means of RT-PCR and flow cytometry. Modified Boyden chambers were used for chemotaxis assay. Results Human mast cells express VEGF-A, VEGF-B, VEGF-C, and VEGF-D at both the mRNA and protein level. Prostaglandin E2 (PGE2 ) enhanced the expression of VEGFA , VEGFB , and VEGFC , whereas an adenosine analog (5′-N-ethylcarboxamido adenosine NECA) increased VEGFA , VEGFC , and VEGFD expression. In addition, PGE2 and NECA enhanced VEGF-A release, and supernatants of PGE2 - and NECA-activated human lung mast cells induced angiogenic responses in the chorioallantoic membrane assay that were inhibited by an anti-VEGF-A antibody. Mast cells expressed mRNA for VEGFR1 and VEGFR2 . These receptors were present on the mast cell surface. VEGF-A165 , VEGF-B167 , VEGF-C, VEGF-D, and placental growth factor 1 induced mast cell chemotaxis. These chemotactic effects were mediated by the activation of both VEGFR-1 and VEGFR-2. Conclusion Our data indicate that human mast cells are both a source and a target of angiogenic and lymphangiogenic factors and therefore might play a role in inflammatory and neoplastic angiogenesis through the expression of several forms of VEGFs and their receptors.
Angiogenesis, the growth of new blood vessels from pre-existing vessels, occurs physiologically in wound healing, during inflammatory diseases, and in tumor growth. Lymphangiogenesis can be activated ...in inflammation and tumor metastasis. The family of vascular endothelial growth factors (VEGFs) and angiopoietins are essential for angiogenesis and lymphangiogenesis. The angiogenic process is tightly regulated by VEGFs, angiopoietins, and endogenous inhibitors. VEGFs and angiopoietins exert their effects by activating specific receptors present on blood and lymphatic endothelial cells. There is now compelling evidence that cells of innate and adaptive immunity (macrophages, mast cells, neutrophils, eosinophils, lymphocytes) are a major source of angiogenic and lymphangiogenic factors. Chronic inflammatory skin diseases such as psoriasis and atopic dermatitis are characterized by altered angiogenesis, lymphangiogenesis, or both. Also such acute inflammatory skin disorders as urticaria, ultraviolet B–induced damage, and angioedema are associated with changes in angiogenic factors. In systemic sclerosis there is a switch from proangiogenic to antiangiogenic factors that play a role in the defective vascular process of this disorder. As yet, there are no clinical trials showing that canonical VEGF/VEGF receptor-targeted strategies can modulate inflammatory skin diseases. Novel strategies targeting other angiogenic/lymphangiogenic pathways should also be investigated.
Background Secreted phospholipases A2 (sPLA2 s) are released in plasma and other biologic fluids of patients with inflammatory, autoimmune, and allergic diseases. Objective We sought to evaluate ...sPLA2 activity in the bronchoalveolar lavage fluid (BALF) of asthmatic patients and to examine the expression and release of sPLA2 s from primary human lung mast cells (HLMCs). Methods sPLA2 activity was measured in BALF and supernatants of either unstimulated or anti-IgE–activated HLMCs as hydrolysis of oleic acid from radiolabeled Escherichia coli membranes. Expression of sPLA2 s was examined by using RT-PCR. The release of cysteinyl leukotriene (LT) C4 was measured by means of enzyme immunoassay. Results Phospholipase A2 (PLA2 ) activity was higher in the BALF of asthmatic patients than in the control group. BALF PLA2 activity was blocked by the sPLA2 inhibitors dithiothreitol and Me-Indoxam but not by the cytosolic PLA2 inhibitor AZ-1. HLMCs spontaneously released a PLA2 activity that was increased on stimulation with anti-IgE. This PLA2 activity was blocked by dithiothreitol and Me-Indoxam but not by AZ-1. HLMCs constitutively express mRNA for group IB, IIA, IID, IIE, IIF, III, V, X, XIIA, and XIIB sPLA2 s. Anti-IgE did not modify the expression of sPLA2 s. The cell-impermeable inhibitor Me-Indoxam significantly reduced (up to 40%) the production of LTC4 from anti-IgE–stimulated HLMCs. Conclusions sPLA2 activity is increased in the airways of asthmatic patients. HLMCs express multiple sPLA2 s and release 1 or more of them when activated by anti-IgE. The sPLA2 s released by mast cells contribute to LTC4 production by acting in an autocrine fashion. Mast cells can be a source of sPLA2 s in the airways of asthmatic patients.
Background Histamine modulates several functions in human monocytes, macrophages, and dendritic cells. However, responses elicited by histamine differ depending on cell type, suggesting variable ...expression of histamine receptors in the monocyte/macrophage lineage. Objective We sought to examine whether the expression of H1 receptors was regulated by cell differentiation of human monocytes into macrophages or dendritic cells. Methods Expression of H1 receptor was evaluated by RT-PCR and western blot in monocytes, monocyte-derived macrophages (MDMs), monocyte-derived dendritic cells (DCs) and human lung macrophages (HLMs). Results Expression of H1 receptor mRNA and protein was higher in HLMs and DCs than in monocytes. H1 expression was approximately 15-fold and 4-fold higher in MDMs and HLMs, respectively, as compared with that seen in monocytes. H1 receptor protein was undetectable in monocytes, whereas it was conspicuous in MDMs. Simultaneous analysis of H2 and H1 mRNA expression indicated that the H2 /H1 ratio decreased from 202.7 ± 14.8 in monocytes to 2.2 ± 0.4 in MDM and 39.5 ± 5.0 in DCs. Incubation of monocytes with histamine neither affected intracellular Ca2+ concentrations nor influenced IL-8 production. In contrast, histamine rapidly induced a Ca2+ signal and stimulated IL-8 production in MDMs. Both effects were inhibited by H1 blockade with levocetirizine, but not by H2 blockade with ranitidine. Conclusions Differentiation of monocytes into macrophages or dendritic cells is associated with profound changes of histamine receptor expression. Upregulation of H1 receptors confers on macrophages the capacity of being activated by histamine. Clinical implications Regulation of H1 and H2 receptor expression in the monocyte/macrophage lineage can be relevant to the pathogenesis of allergic inflammation.
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