Beate M. Henz

Human skin: source of and target organ for angiotensin II

Abstract:u2002 The present study examined the expression of angiotensin receptors in human skin, the potential synthesis of angiotensin II (Ang II) in this location and looked for a first insight into physiological functions. AT1 and AT2 receptors were found within the epidermis and in dermal vessel walls. The same expression pattern was found for angiotensinogen, renin and angiotensin‐converting enzyme (ACE). All components could additionally be demonstrated at mRNA level in cultured primary keratinocytes, melanocytes, dermal fibroblasts and dermal microvascular endothelial cells, except for AT2 receptors in melanocytes. The ability of cutaneous cells to synthesize Ang II was proved by identifying the molecule in cultured keratinocytes. Furthermore, in artificially wounded keratinocyte monolayers, ACE‐mRNA expression was rapidly increased, and enhanced ACE expression was still found in cutaneous human scars 3 months after wounding. These findings suggest that the complete renin–angiotensin system is present in human skin and plays a role in normal cutaneous homeostasis as well as in human cutaneous wound healing.

Evidence for a restricted rather than generalized stimulatory response of skin-derived human mast cells to substance P

To resolve the controversy regarding substance P (SP) mediated stimulation of mast cells (MC), we demonstrate that SP triggers histamine release from purified human skin MC (sMC), but contrast to stimulation via FcepsilonRI, does not effect the production of TNF-alpha or IL-8. Conversely, both anti-IgE and SP are suppressive in terms of IL-6. By quantitative RT-PCR, the amount of templates at baseline (per 25 ng total RNA) is 2178 (IL-6), 2,665 (IL-8) and 94 (TNF-alpha), and remains unaltered by SP. Contrast to sMC, LAD2 MC respond to SP with stronger histamine release and robust TNF-alpha production in an only partially neurokinin-1R mediated manner, while histamine release of sMC is chiefly mediated by this receptor. We conclude that human sMC are responsive to SP in a selective manner by eliciting degranulation without the induction of cytokines and that SP-triggered cytokine production varies among MC subtypes, likely through differences in signaling mechanisms.

Comparative cytokine profile of human skin mast cells from two compartments—strong resemblance with monocytes at baseline but induction of IL‐5 by IL‐4 priming

Although known as heterogenous, mast cells (MC) are believed to induce allergic inflammation, partially by secretion of T helper cell type 2 (Th2) cytokines. We show here that MC purified from twohuman skin compartments produce cytokines that are primarily associated with inflammation and innate immunity [interleukin (IL)‐1β, IL‐6, IL‐8, tumor necrosis factor α (TNF‐α)]. Although these are detectable even without stimulation, immunoglobulin (Ig)E receptor cross‐linking is able to enhance only TNF‐α production, but phorbol 12‐myristate 13‐acetate additionally promotes IL‐1β and IL‐8. With the exception of TNF‐α, the presence of serum has a positive impact on cytokine production. Although IL‐13 transcripts (but not those for IL‐4 and ‐5) are produced by skin MC, all Th2 cytokines remain undetectable in the supernatants or lysates of MC from foreskin and breast skin by all treatments. Therefore, rather than sharing similarity with Th2 cells, the cytokine profile of skin MC at baseline resembles that of monocytes. Of note, MC precultured in the presence of IL‐4 [alone or plus stem cell factor (SCF)] before anti‐IgE stimulation, acquired the ability to produce IL‐5, and IL‐1β was concomitantly suppressed. Additionally, strong up‐regulation of IL‐6 by SCF was observed, which was inhibited by IL‐4. In summary, we present a detailed analysis of the cytokine array of human skin MC immediately upon isolation; demonstrate that MC from different skin compartments, although producing the same pattern of cytokines, display quantitative differences in several aspects; and provide further evidence that MC possess a proinflammatory capacity, which can, however, be altered by microenvironmental stimuli, substantiating the marked plasticity of the cells.

The transcription factor profile of human mast cells in comparison with monocytes and granulocytes

Abstract.Expression profiles of mRNAs and proteins for various transcription factors were determined for human skin mast cells (sMCs), leukemic HMC-1 MCs, monocytes and granulocytes. By quantitative RT-PCR, sMCs expressed lower levels of c-fos, PU.1, C/EBPα, and C/EBPɛ than monocytes and granulocytes, but higher levels of MITF, SCL, GATA-1 and GATA-2. At the protein level, MITF, SCL, GATA-2, Elf-1 and c-fos were clearly detectable in sMCs. With the exception of c-fos, these proteins were absent or expressed only slightly in monocytes and granulocytes. The expression of NF-E2p45, GATA-1, PU.1, Ets-1, C/EBPα and C/EBPɛ was below the detection limit in sMCs, but detectable in other myelocytes. The high expression of SCL and GATA-2 in sMCs is reminiscent of stem cells. The absence of C/EBPɛ in sMCs, but strong expression in HMC-1, suggests it may impair MC maturation. In summary, mature human MCs can be characterized as C/EBPαlow, C/EBPɛ−, PU.1low, GATA-1low, GATA-2+, SCL+, MITFhigh.

Exploring the mast cell enigma: a personal reflection of what remains to be done

Abstract: Mast cells are traditionally viewed as effector cells of allergic reactions and parasitic diseases, but their importance in host defense against bacteria, in tissue remodelling, their bone marrow and stem cell origin and a central role of the stem cell factor (SCF) as mast cell growth and chemotactic factor has been worked out only in recent years. Despite this, major aspects about the nature of the cells and their role in disease remain unclear. This holds in particular for the identification of mast cell precursors and the role of growth factors that stimulate specific mast cell commitment from stem cells, such as nerve growth factor, neutrotrophin‐3 and certain interleukins, alone and during interaction with SCF. Early data suggesting also an involvement of specific transcription factors need to be expanded in this process. Furthermore, although mast cell proliferative disease (mastocytosis) has been shown to be often associated with SCF receptor c‐kit mutations, reasons for the development of this disease remain unclear. This holds also for mast cell release mechanisms in many types of mast cell‐dependent urticaria. Exciting new insights are emerging regarding the role of mast cells in bacterial infections, in defense against tumors, in wound healing and in the interplay with the nervous system, with hormones, and in the neurohormonal network. The aim of this reflection is to delineate the many known and unknown aspects of mast cells, with a special focus on their development, and to discuss in detail two mast cell‐related diseases, namely mastocytosis and urticaria.

Expression of prothrombin, thrombin and its receptors in human scars

Abstract:u2002 The coagulation system is thought to play a pivotal role during the initial phase of wound healing, but mechanisms and cells involved are only partly understood. We have therefore examined human scars for the expression of thrombin, its precursor prothrombin and the thrombin receptors, thrombomodulin (TM) and protease‐activated receptor‐1 (PAR‐1), compared with normal skin. Biopsies of scars were obtained from primary excision sites of melanoma patients (nu2003=u200320) and were compared with normal skin distant from the scar (nu2003=u200310), using immunohistochemistry. In addition, polymerase chain reaction analyses were performed on scar versus normal tissue and on cultured keratinocytes, fibroblasts and endothelial cells before and after stimulation with selected cytokines known to be active in wound healing. Normal epidermis was stained for prothrombin, thrombin, TM and PAR‐1, and dermal tissue was stained only for TM and PAR‐1. In scar tissue, thrombin and TM were upregulated in the epidermis and all four molecules in the dermis, independent of the age of the scars. In tissue extracts, mRNA expression of PAR‐1 and prothrombin expression were, however, unchanged and TM even slightly decreased in scars, compared with normal skin. On analysis of cultured cells, keratinocytes expressed mRNA for PAR‐1, TM and prothrombin, endothelial cells for PAR‐1 and TM, and fibroblasts for PAR‐1. An upregulation of PAR‐1 mRNA was induced in fibroblasts on exposure to tumor necrosis factor‐α (TNF‐α), while it remained unchanged in endothelial cells in response to TNF‐α. A downregulation of TM was induced in endothelial cells on exposure to TNF‐α. These findings, showing a marked modulation of thrombin, PAR‐1 and TM even in older human scar tissue, suggest that the coagulation system is not only involved during clotting, but also during the inflammatory and tissue remodelling phases of wound healing.

The European competence network on mastocytosis (ECNM)

SummaryThe European Competence Network on Mastocytosis (ECNM) is a Europe-wide, multinational cooperative approach attempting to improve recognition, diagnosis, and therapy of mastocytosis. The network is composed of local centers, physicians, and scientists who have dedicated their work to patients with mastocytosis. However, because of the rarity and complexity of the disease, each single component in the network alone would fail to meet important demands and to reach solid conclusions in this field of applied medicine. The ECNM represents an attempt to overcome this restriction as a cooperative multicenter platform that should serve as an important basis for the development of new therapeutic strategies and diagnostic concepts and for the standardization of techniques used to determine diagnostic and prognostic parameters. Moreover, using future central databases and registries, a suitable infrastructure for the development of cooperative multicenter clinical trials will be established. In addition, the ECNM is dedicated to provide the best available information about the disease to patients and physicians.ZusammenfassungDas Europäische Kompetenznetzwerk für Mastozytosen (ECNM) ist ein europaweiter multinationaler Ansatz, der darauf abzielt, die Erkennung, Diagnostik und Therapie der Mastozytosen nachhaltig zu verbessern. Das Netzwerk besteht aus lokalen Zentren, Ärzt(inn)en und Wissenschafter(inne)n, welche die Mastozytosen schwerpunktmäßig beforschen. Aufgrund der Seltenheit und Komplexität der Erkrankung würde aber jede einzelne Komponente des Netzwerkes für sich alleine zu keinen aussagekräftigen Ergebnissen kommen. Das ECNM spielt hier als kooperative Plattform eine wichtige Rolle und bietet als solche sowohl für die Entwicklung von neuen therapeutischen und diagnostischen Konzepten als auch für die Standardisierung von diagnostischen und prognostischen Parametern eine wichtige Basis. Zusätzlich sollen zentrale Datenbanken geschaffen werden, die als Basis für die Entwicklung von multizentrischen Studien dienen können. Überdies ist das Netzwerk bestrebt, den Patient(inn)en und Ärzt(inn)en die jeweils aktuellen Informationen über die Erkrankung und ihre Entitäten zukommen zu lassen.