Search

Background: Mast cells are resident tissue cells that induce anaphylactic reactions by rapidly releasing mediators after antigen-mediated cross-linking of immunoglobulin E receptors. In the similarly active peripheral blood basophilic leukocyte, lysosome-associated membrane protein 3 (LAMP-3; CD63) has been described as an activation marker, but LAMPs have not been investigated in normal tissue mast cells., Methods: Intra- and extracellular expressions of LAMP-1 (CD107a), LAMP-2 (CD107b), and LAMP-3 (CD63) were analysed by flow cytometry, immunocytochemistry, and functional assays in unstimulated and stimulated leukemic human mast cell line 1 (HMC-1) and skin mast cells., Results: On flow cytometry, all mast cells expressed LAMP-3 at their cell membranes, whereas LAMP-1 and LAMP-2 were barely detectable (HMC-1 cells) or expressed at low levels (<10% of skin mast cells). After fixation and permeabilisation, high intracellular levels of all three LAMPs were noted in both cell types. After stimulation, a rapid translocation of intracellular LAMPs to the cell membrane, with an associated release of histamine, leukotriene C(4) and prostaglandin D(2), was ascertained in skin mast cells only., Conclusion: These results show that LAMP-1 and LAMP-2 are activation markers for normal mast cells. The lack of LAMP translocation after activation of leukemic mast cells may be related to maturation or malignancy-associated defects of these cells., (Copyright 2004 Wiley-Liss, Inc)

Mast cells generate and release histamine during anaphylactic reactions, and there is pharmacological evidence that histamine regulates this process via specific receptors. Therefore, we examined human leukemic (HMC-1) and normal skin mast cells for the expression of all four currently known histamine receptors. Both cell types expressed H2 and H4 receptors at mRNA and protein levels, whereas H3 receptor specific mRNA and receptor protein was undetectable. Similarly, immunohistochemistry of cutaneous tissue showed an absence of H3 receptor in these cells. Despite transcription of mRNA, H1 receptor protein was only moderately expressed in HMC-1 cells and was virtually absent in skin mast cells. Furthermore, only H1, H2, and H4 receptors were detectable by Western blot analysis of HMC-1 cells. Radiolabeled histamine binding was strongly inhibited only by H2 (ranitidine)- and H3/H4 (FUB 108)-specific antagonists. Histamine-induced increase of cAMP was inhibited by the H2 receptor antagonist famotidine, whereas induction of IP3 was not observed, making signaling via the H1 receptor unlikely. These data show that human mast cells constitutively express primarily H2 and H4 receptors and that H2 receptors are functionally linked to cellular processes. They provide new insights into the mechanisms that govern auto- and paracrine histamine-induced mast cell functions.

The vanilloid receptor subtype 1 (VR1)/(TRPV1), binding capsaicin, is a non-selective cation channel that recently has been shown in human keratinocytes in vitro and in vivo. However, a description of VR1 localization in other cutaneous compartments in particular cutaneous nerve fibers is still lacking. We therefore investigated VR1 immunoreactivity as well as mRNA and protein expression in a series (n = 26) of normal (n = 7), diseased (n = 13) [prurigo nodularis (PN) (n = 10), generalized pruritus (n = 1), and mastocytosis (n = 2)], and capsaicin-treated human skin (n = 6). VR1 immunoreactivity could be observed in cutaneous sensory nerve fibers, mast cells, epidermal keratinocytes, dermal blood vessels, the inner root sheet and the infundibulum of hair follicles, differentiated sebocytes, sweat gland ducts, and the secretory portion of eccrine sweat glands. Upon reverse transcriptase-polymerase chain reaction and Western blot analysis, VR1 was detected in mast cells and keratinocytes from human skin. In pruritic skin of PN, VR1 expression was highly increased in epidermal keratinocytes and nerve fibers, which was normalized after capsaicin application. During capsaicin therapy, a reduction of neuropeptides (substance P, calcitonin gene-related peptide) was observed. After cessation of capsaicin therapy, neuropeptides re-accumulated in skin nerves. In conclusion, VR1 is widely distributed in the skin, suggesting a major role for this receptor, e.g. in nociception and neurogenic inflammation.

Lippert U, Zachmann K, Henz BM, Neumann C. Human T lymphocytes and mast cells differentially express and regulate extra- and intracellular CXCR1 and CXCR2. CXCL8 plays a major role in cell recruitment to sites of inflammation. Apart from neutrophils, little is known, however, about the cellular distribution and regulation of CXCL8 receptors in cells involved in acquired and adaptive immune responses. In previous studies, we have demonstrated the extracellular expression and function of CXCR1/2 on mast cells and also detected an intracellular pool of CXCR1/2. Here, we have addressed the question of receptor regulation during stimulation of human mast cells (HMC-1 cell line) and have studied T cells in comparison. Cell permeabilization was performed to detect both surface and possible intracellular receptor pools. HMC-1 cells stained positive for both receptors on the cell surface (CXCR1, 50%; CXCR2, 51%) and also after cell permeabilization (CXCR1, 86%; CXCR2, 74%). Similarly, T cells exhibited both cell-surface receptor expression (CXCR1, 30%; CXCR2, 23%) and higher total receptor expression (CXCR1, 50%; CXCR2, 36%), although overall values were lower than that in HMC-1 cells. On immunoblot, molecular weights of extra- and intracellular receptors on mast cells were the same, excluding altered receptor glycosylation. On stimulation with phorbol 12-myristate 13-acetate plus calcium ionophore, a time-dependent decrease of surface-membrane receptors was observed in both cell types, while total receptor remained the same, suggesting that receptor shedding is not involved. The kinetics of membrane receptor internalization and replenishment differed for the two cell types. Furthermore, receptor internalization was associated with decreased F-actin polymerization, a basic prerequisite for cell migration. These findings demonstrate for the first time the expression of extra- and intracellular CXCR1/2 receptors on T cells and delineate the dynamics of CXCR1/2 receptors on mast cells and T cells. Furthermore, they suggest a cell-type-specific and finely tuned regulation of chemokine responses at the receptor level in the context of inflammation. [ABSTRACT FROM AUTHOR]

Since mast cells and basophils are thought to play a central role in several types of cutaneous inflammatory and allergic reactions and since interleukin-6 (IL-6) is an important mediator in these processes, we have studied the ability of the human mast cell line HMC-1, the human basophilic cell line KU812 and human skin mast cells to produce IL-6. All three cell types proved to be potent sources of this cytokine after appropriate stimulation. Transcription of IL-6 mRNA was first detectable 2 h after stimulation with the ester phorbol myristate acetate (PMA) and the calcium ionophore A23187 in both cell lines, as evidenced by semiquantitative reverse transcriptase polymerase chain reaction analysis. Whereas resting cells did not produce IL-6 protein, PMA/A23187- stimulated cells released immunoreactive and biologically active IL-6, as demonstrated and quantitated by enzyme-linked immunosorbent assay and by the use of TEPC 1033 cells an IL-6-dependent murine plasmacytoma cell line. Stimulated KU812 cells secreted sevenfold more IL-6 (up to 15 ng/ml) than HMC-1 cells (up to 2.4 ng/ml). Immunoblotting of HMC-1- and KU812 cell-derived IL-6 revealed several IL-6 forms in the molecular weight range of 2l to 30 kDa. Immunoelectron microscopic studies of human skin biopsies provided evidence that unstimulated mast cells do not contain preformed IL-6 but accumulate IL-6 in cytoplasmic and extruded granules after IgE-dependent stimulation. These findings suggest that IL-6 secreted by human mast cells and basophils potentially contributes to allergic, other immunologically mediated and nonspecific inflammatory responses. [ABSTRACT FROM AUTHOR]