Ultraviolet B radiation exerts enhancing effects on the production of a complement component, C3, by interferon-gamma-stimulated cultured human epidermal keratinocytes, in contrast to photochemotherapy and ultraviolet A radiation that show suppressive effects

Psoriatic Dermal-Derived Mesenchymal Stem Cells Induced C3 Expression in Keratinocytes

Purpose

Patients and Methods

Results

Conclusion

IFN-gamma upregulates expression of the mouse complement C1rA gene in keratinocytes via IFN-regulatory factor-1

We examined the expression of the mouse complement component C1rA (mC1rA) in IFN-gamma-stimulated mouse keratinocytes (Pam 212) and found that it was upregulated. To analyze the mechanism involved, we cloned the 2,150 bp 5'-flanking region of mC1rA by the vectorette-PCR technique, and identified the transcription start site of mC1rA by rapid amplification of complementary DNA ends. Analysis of the 5' sequence revealed putative binding sites for activator protein 1, CCAAT/enhancer binding protein (C/EBP), signal transducer and activator of transcription 1 (STAT-1), IFN-regulatory factor-1 (IRF-1), and others. We detected transcriptional activation dependent on this upstream region in reporter gene assays and Northern blots. To identify the cis-acting regulatory elements involved, we analyzed serial deletion constructs of the promoter using luciferase reporters. The -80 to -19 bp region, which contains a putative IRF-1 binding site, was required for both basal promoter activity and responses to IFN-gamma. The use of site-directed point mutations, electrophoresis mobility shift assays, and supershift assays indicated that the putative IRF-1 binding site was essential for both IFN-gamma-dependent and -independent transcriptional activity of the mC1rA promoter. We conclude that IFN-gamma stimulates mC1rA gene expression via IRF-1 in mouse keratinocytes.

Induction of C3 and CCL2 by C3a in keratinocytes: a novel autocrine amplification loop of inflammatory skin reactions

The complement fragment-3a (C3a) acts via a G protein-coupled C3aR and is of importance in allergic and inflammatory diseases. Recent studies suggest the presence of complement proteins in the epidermal compartment and synthesis of some of these proteins (C3, factor B, and factor H) by human primary keratinocytes (KCs) during inflammation. However, expression of C3aR and its role in human KCs is not elucidated thus far. In this study, we demonstrate the expression of C3aR on KCs as detected by quantitative real-time RT-PCR and flow cytometry. IFN-gamma and IFN-alpha strongly up-regulated the surface expression of C3aR on KCs among all other cytokines tested. After up-regulation of C3aR by IFN-gamma and IFN-alpha, we observed the induction of five genes (CCL2, CCL5, CXCL8, CXCL10, and C3) after stimulation of KCs with C3a in microarray analysis. We confirmed the induction of C3 and CCL2 at RNA and protein levels. Furthermore, incubation of C3 with skin mast cells tryptase resulted in the generation of C3 fragments with C3a activity. In conclusion, our data illustrate that epidermal KCs express functional C3aR. The increases of C3 and CCL2 synthesis by C3a and C3 activation by skin mast cell tryptase delineates a novel amplification loop of complement activation and inflammatory responses that may influence the pathogenesis of allergic/inflammatory skin diseases.

In situ profiling and quantification of cytokines released during ultraviolet B-induced inflammation by combining dermal microdialysis and protein microarrays

In skin, an evolving inflammatory or immune response is triggered by early release of a cytokine cascade into the extracellular space. Investigation of extracellular cytokine secretion in situ has been limited by low cut-off filtering membranes and sample volume size and the inability to monitor changes in cytokine protein levels in real-time in situ. Here, we combine for the first time the methods of intradermal microdialysis and antibody protein arraying to profile the early cascade of multiple cytokines in a complex inflammatory response exemplified by ultraviolet B (UVB)-induced inflammation. We observed significant differences of the cytokine and growth factor responses after tissue injury by catheter placement and UVB-induced inflammation. UVB irradiation initiates a rapid proinflammatory response followed by a mixed TH1/TH2 response in which ultimately TH2 cytokines IL-4 and IL10 predominated after 24 h. This most likely indicates the termination and self limitation of the inflammatory response. We conclude that the combination of dermal microdialysis and protein microarray offers a powerful tool to analyze in real-time the complex and rapidly changing interstitial protein milieu during cutaneous inflammatory responses.

Ultraviolet-B recruits mannose-binding lectin into skin from non-cutaneous sources

Mannose-binding lectin (MBL) is an integral part of the innate immune system and functions as an opsonin by binding to pathogens and certain apoptotic cells to promote their uptake by phagocytes. We recently identified an association of low-producing MBL polymorphisms with adult dermatomyositis (DM). Our model is that MBL deficiency leads to a defect in the clearance of apoptotic debris in the skin, thereby predisposing to photosensitive autoimmune disease. In this study, we sought to determine whether MBL binds within the epidermis, and to determine its source, and potential function of this binding. We demonstrated that the MBL is present in irradiated, but not in non-irradiated skin, and in irradiated skin it is bound to apoptotic keratinocytes (KC). We found that MBL is not made by KC, showing indirectly that it comes from an exogenous source, despite the fact that other complement components are made by KC and upregulated by ultraviolet irradiation. Finally, we demonstrated that non-KC-derived MBL bound to apoptotic KC in vitro and increased the uptake of these cells by dendritic cells. We hypothesize that MBL may facilitate non-inflammatory clearance of apoptotic debris in patients with photosensitive forms of DM.

Ultraviolet-radiation-induced keratinocyte apoptosis in C1q-deficient mice

Exposure to ultraviolet B radiation is an important trigger of both systemic and cutaneous disease flares in individuals with systemic lupus erythematosus. More than 90% of individuals with homozygous C1q deficiency develop a systemic-lupus-erythematosus-like illness, which is typically associated with a severe photosensitive rash. Apoptotic, human keratinocytes have been shown in vitro to bind C1q, in the absence of antibody. These observations, together with the hypothesis that a major source of the autoantigens driving the immune response in systemic lupus erythematosus comes from apoptotic cells, led us to investigate the effects of murine C1q deficiency on ultraviolet-radiation-induced keratinocyte apoptosis in vivo. In this work, we demonstrated C1q binding to apoptotic murine keratinocytes in vitro and showed for the first time that C1q is also present on sunburn cells in vivo. In addition to C1q, we detected C3 deposition on sunburn cells in both wild-type and C1q-deficient mice, suggesting activation of the alternative pathway. Following acute ultraviolet exposure in vivo, no difference in the rate of clearance of sunburn cells was found in C1q-deficient mice from three different genetic backgrounds, compared with strain-matched wild-type controls. Furthermore, chronic ultraviolet exposure did not result in the production of autoantibodies or the development of glomerulonephritis. Our findings suggest that C1q does not play a critical role in the physiologic clearance of apoptotic murine keratinocytes in vivo.