Ultraviolet radiation and skin mast cells: Effects, mechanisms and relevance for skin diseases

Mast cells (MCs) are well known as versatile effector cells in allergic reactions and several other immune responses. Skin MCs and cutaneous MC responses are subject to the effects of environmental factors including ultraviolet radiation (UVR). Numerous studies have assessed the effects of UVR on MCs, in vitro and in vivo. Interestingly, UVR seems to have variable effects on non-activated and activated mast cells. In general, UV therapy is beneficial in the treatment of urticaria and mastocytosis, but the effects are variable depending on treatment regimen and type of UVR. Here, we review and summarise key reports from the older and current literature on the crosstalk of UVR and skin MCs. Specifically, we present the literature and discuss published reports on the effects of UVR on skin MCs in rodents and humans. In addition, we review the role of MCs in UVR-driven skin diseases and the influence of UV light on MC-mediated skin diseases. This summary of our current understanding of the interplay of skin MCs and UVR may help to improve the management of patients with urticaria and other MC disorders, to identify current gaps of knowledge, and to guide further research.

A novel method to generate and culture human mast cells: Peripheral CD34+ stem cell-derived mast cells (PSCMCs)

The identification and characterization of human mast cell (MC) functions are hindered by the shortage of MC populations suitable for investigation. Here, we present a novel technique for generating large numbers of well differentiated and functional human MCs from peripheral stem cells (=peripheral stem cell-derived MCs, PSCMCs). Innovative and key features of this technique include 1) the use of stem cell concentrates, which are routinely discarded by blood banks, as the source of CD34+ stem cells, 2) cell culture in serum-free medium and 3) the addition of LDL as well as selected cytokines. In contrast to established and published protocols that use CD34+ or CD133+ progenitor cells from full blood, we used a pre-enriched cell population obtained from stem cell concentrates, which yielded up to 10(8) differentiated human MCs per batch after only three weeks of culture starting with 10(6) total CD34+ cells. The total purity on MCs (CD117+, FcεR1+) generated by this method varied between 55 and 90%, of which 4-20% were mature MCs that contain tryptase and chymase and show expression of FcεRI and CD117 in immunohistochemistry. PSCMCs showed robust histamine release in response to stimulation with anti-FcεR1 or IgE/anti-IgE, and increased proliferation and differentiation in response to IL-1β or IFN-γ. Taken together, this new protocol of the generation of large numbers of human MCs provides for an innovative and suitable option to investigate the biology of human MCs.

A long-term coculture model for the study of mast cell-keratinocyte interactions

Physiologic and pathologic events associated with cutaneous differentiation and repair are the result of a concerted action of various types of resident tissue cells. In vitro models simulating this complex in vivo situation are therefore needed to clarify the specific contribution and relevant interaction of, for example, dermal mast cells with other major cutaneous cells. The aim of this study was to establish a long-term coculture model that includes dermal mast cells, dermal fibroblasts, and keratinocytes in a human skin equivalent organotypic setting. Normal dermal mast cells and fibroblasts (1:4) were enclosed in collagen gel and normal keratinocytes were grown on top with exposure to the air interface. Under these conditions, mast cell integrity and functionality was preserved even after 4 wk of culture, as shown by electron microscopy and immunohistochemistry using antibodies against the mast-cell-specific granule enzyme tryptase and the receptors for stem cell factor and IgE. Mast cells also released histamine on stimulation with anti-IgE, and on ultrastructure were found to degranulate, with decrease of granule matrix density and formation of cell-cell contacts with fibroblasts. After 2 wk of culture, keratinocytes had formed an epidermis-like multilayer and were able to proliferate and differentiate, as shown by bromodeoxyuridine incorporation of basal cells and immunohistochemical staining for transglutaminase and cytokeratins 1 and 10. The model presented here thus provides a potentially relevant tool to further clarify the interaction of dermal mast cells with major other skin cells and their contribution to cutaneous physiology, repair processes, and pathology.

Chronic porcine two-hit model with hemorrhagic shock and Pseudomonas aeruginosa sepsis

BACKGROUND

Sepsis is still a major cause of death despite well-developed therapeutical strategies such as antibiotics and supportive medication. The aim of this study was to characterize the long-term effects of a two-hit porcine sepsis model with a hemorrhagic shock as 'first hit' followed by a Pseudomonas aeruginosa infusion as 'second hit'.

MATERIALS AND METHODS

Twelve juvenile healthy pigs were anesthetized and hemodynamically monitored. The two-hit group (n = 6) underwent a hemorrhagic shock with a 50% reduction of the mean arterial pressure and/or cardiac index for 45 min, followed by resuscitation, while the control group (n = 6) received no pretreatment. All chronically catheterized conscious pigs were challenged with a P. aeruginosa infusion (1.6 x 10(7) CFU/kg/h for the first 24 h followed by 1.6 x 10(6) CFU/kg/h for the next 24 h) and observed for another 48 h.

RESULTS

The two-hit group showed the following significant differences to the control group: higher APACHE II scores prior to sepsis induction, increased persisting mean pulmonary arterial pressure (MPAP) and pulmonary vascular resistance index (PVRI) during bacterial challenge. In contrast, systemic vascular resistance (SVRI) was reduced at the end of the study. Throughout the observation period, the mean arterial pressure (MAP) was significantly reduced.

CONCLUSIONS

The present study shows that the clinical course and hemodynamic effects of a P. aeruginosa sepsis will be aggravated by a preceding hemorrhagic shock during an observation period of 96 h. This two-hit model represents a valid, clinically relevant experimental protocol in sepsis research.