Synthesis of Complement Components C3 and Factor B in Human Keratinocytes is Differentially Regulated by Cytokines

Abstract

The complement system plays an important part in host defense and inflammation. Locally synthesized complement may perform these functions at tissue and organ level. In skin the keratinocyte is the major cell type, it is known to produce two soluble complement components, C3 and factor B. In this study we investigated the regulation of synthesis of these components in foreskin keratinocytes by cytokines. Human keratinocytes were cultured in the presence of supernatant of activated peripheral blood mononuclear cells, interleukin-1alpha, interleukin-2, interleukin-6, transforming growth factor-beta1, tumor necrosis factor-alpha, or interferon-gamma. C3 and factor B proteins were measured in culture supernatant by enzyme-linked immunosorbent assay and C3 and factor B transcripts in harvested cells by reverse transcriptase-polymerase chain reaction. Cultured keratinocytes constitutively produced C3 and factor B. Supernatant of activated mononuclear cells upregulated C3 and factor B production by 27- and 15-fold, respectively. interleukin-1alpha, interferon-gamma, and tumor necrosis factor-alpha upregulated C3 synthesis by 7-, 8-, and 22-fold, and interleukin-1alpha, interleukin-6, and interferon-gamma upregulated factor B synthesis by 3-, 3-, and 34-fold, respectively. Tumor necrosis factor-alpha induced production of C3 and interferon-gamma induced production of factor B were inhibited by cycloheximide. Cytokine induced upregulation of C3 and factor B proteins was always associated with the upregulation of levels of C3 and factor B mRNA. This indicated that, as expected, cytokine-induced enhancement in C3 and factor B levels was due to an increase in synthesis rather than their possible release from intracellular stores. In conclusion, synthesis of C3 and factor B in keratinocytes is regulated by some cytokines, known to be produced by inflammatory cells and keratinocytes.

Activation of the complement system generates antibacterial peptides

“…In blood the concentration of C3 is 5-11 M, and therefore, local complement activation should induce generation of C3a and C3a-desArg at antibacterial concentrations. During wound healing and inflammation, local synthesis of C3 by monocytes and keratinocytes may constitute a significant additional source of C3a at epithelial surfaces (20,26). Indeed, analogously to other AMPs such as defensins and LL-37 (27), C3a is present in psoriatic skin (28), which in part may explain the lower occurrence of bacterial infections in patients with psoriasis than in patients with atopic dermatitis (29).…”

Induction of C3 and CCL2 by C3a in Keratinocytes: A Novel Autocrine Amplification Loop of Inflammatory Skin Reactions

“…Recently, KCs have been described as a rich source of C3 (23). In KCs, induction of C3 by C3a clearly suggests the amplification of C3a mediated effects in an autocrine fashion.…”

“…4 A, skin mast cell-derived tryptase generated C3a from C3. KCs stimulated with IFN-␥ and TNF-␣ are rich sources of C3 (23). Incubation of supernatant from IFN-␥ and TNF-␣ stimulated KCs with 0.2 g of skin mast cell tryptase for 1 h at 37°C resulted in generation of C3a (Fig.…”

“…Epidermal keratinocytes (KCs) constitutively secrete C3, factor B, and factor H and have been shown to release high amounts of C3 after stimulation with proinflammatory cytokines (22,23). Increased levels of C3a in the circulation have been found in diseases such as adult respiratory distress syndrome (24), asthma (25), psoriasis, and atopic dermatitis (AD) (26).…”

Human Skin Mast Cells Express Complement Factors C3 and C5

“…Although most of the C3 and C5 in the circulation are produced by the liver, their extrahepatic production by various cell types, including macrophages, dendritic cells, fibroblasts, epithelial cells, endothelial cells, keratinocytes, smooth muscle cells, and neuronal cells, either spontaneously or in response to cytokine stimulation, has been well documented (29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40)(41). Locally synthesized C3 and C5, presumably through their bioactive metabolites, importantly regulate other aspects of inflammation and host defense (42,43), for example, clearance of immune complexes by macrophages (44).…”