Interleukin 6 stimulates synthesis of complement proteins factor B and C3 in human skin fibroblasts

The secretion of the third component of complement (C3) by human polymorphonuclear leucocytes from both normal and systemic lupus erythematosus cases

Recently, murine peritoneal exudate polymorphonuclear leucocytes (PMNs) have been proved to secrete complement C3. In this report we show the secretion of C3 by normal human blood PMNs. ELISA assay was used to detect secreted C3 in culture supernatants of PMNs, while immunoperoxidase staining was used for intracellular C3 detection. 12-o-tetradecanoyl phorbol 13 acetate (TPA) had a flushing effect on C3 secretion by PMNs but not macrophages, suggesting a special C3 storing capability in PMNs. Dioctanoyl glycerol, mezerein and calcium ionophore A23187 caused the same marked increase in C3 secretion by PMNs. This suggests the contribution of protein kinase C and the calmodulin pathway in the mechanism of C3 secretion, similar to murine peritoneal exudate PMNs. In some cases of systemic lupus erythematosus, C3 secretion by blood PMNs was increased but no similar response to TPA could be detected.

Interleukin-6 messenger RNA expression and interleukin-6 protein secretion in cells isolated from normal human bone: regulation by interleukin-1

Recent evidence suggests that cytokines, in addition to regulating hematopoiesis and immune functions, may be important paracrine regulators of bone turnover. Interleukin-1 (IL-1) and IL-6 are cytokines that are produced by and affect both hematopoietic and nonhematopoietic cell types. IL-1 stimulates bone resorption and inhibits osteoblast proliferation and collagen production. Previous reports that IL-6 was secreted in murine osteoblast and bone organ cultures in response to IL-1 and PTH suggested that IL-6 has paracrine effects on bone resorption or formation. To determine whether IL-6 has a paracrine function in human bone, IL-6 expression in cells isolated from normal human bone was investigated. IL-6 mRNA levels in untreated cultures were low and variable, and IL-6 secretion was undetectable. PTH had no effect on IL-6 mRNA levels or IL-6 secretion. IL-1 beta increased IL-6 mRNA levels, maximally 40-fold at 12 h. IL-1 beta increased IL-6 secretion to 0.13 nM, more than 80-fold that of untreated controls at 12 h. IL-1 beta also increased IL-1 beta mRNA levels, maximally 9-fold at 12 h, but did not increase cellular levels or secretion of IL-1 beta protein. Recombinant human IL-6 at 0.5-5 nM stimulated resorption in neonatal mouse calvarial organ cultures but had no effect on human bone-derived cell DNA synthesis or type I procollagen mRNA levels. The results suggest that IL-6 production by human osteoblasts may function to enhance osteolytic activity of IL-1 but does not affect proliferative and matrix biosynthetic aspects of bone formation that were tested. Because osteoblasts and bone marrow cells are in close proximity, IL-6 produced by osteoblasts may also function to amplify IL-1 stimulation of immune responses and hematopoiesis in bone marrow.

Stimulation of collagen and glycosaminoglycan production in cultured human adult dermal fibroblasts by recombinant human interleukin 6

Interleukin (IL) 6 is a pleiotropic cytokine synthesized by fibroblasts in response to many stimuli, including IL-1 beta. To evaluate the possibility that previously observed stimulation of fibroblast biosynthetic functions by IL-1 beta may be mediated by autocrine IL-6, we investigated the effect of recombinant human (rh) IL-6 on the connective tissue-related biosynthetic functions of three lines of cultured human adult dermal fibroblasts. We found that rhIL-6 mimicked some of the activities of IL-1 beta, as 24-96-h treatment of confluent fibroblast cultures with rhIL-6 caused concentration (10 to 1000 ng/ml)-dependent increases in the production of collagen and the glycosaminoglycans (GAG), hyaluronic acid and chondroitin-4/6-sulfates, but had little effect on fibronectin or total protein production. Although the effective stimulating concentrations of IL-6 were within the range (approximately 100 ng/ml) we found produced by rhIL-1 beta-treated fibroblast cultures, rhIL-1 beta at 0.2-1.0 ng/ml induced significantly greater amounts of collagen and GAG than the maximum effective concentrations of IL-6. Moreover, an anti-rhIL-6 antibody, which effectively neutralized the fibroblast-stimulating activities of rhIL-6, only fractionally blocked the fibroblast-stimulating actions of rhIL-1 beta, suggesting autocrine IL-6 only partially mediates the effects of IL-1 beta on fibroblasts. Conversely, the fibroblast-stimulating effects of rhIL-6 are unlikely due to autocrine IL-1 beta, as an anti-rhIL-1 beta antibody had only minimal inhibitory action on rhIL-6-treated fibroblast cultures. Overall these results suggest that IL-6 could function as a paracrine/autocrine regulator of dermal fibrotic repair.

Extrahepatic expression of plasma protein genes during inflammation

The body's protective responses to infection, wounding, trauma, and malignancy include the acute-phase reaction, which is modulated by various cytokines and their cellular receptors. During the acute-phase reaction, levels of specific proteins synthesized by the liver increase in the plasma. Little information is available about the extrahepatic synthesis of plasma proteins during the acute-phase reaction. The study described here analyzes the tissue-specific expression of genes encoding the plasma proteins albumin (ALB), alpha 1-antitrypsin (AAT), transferrin (TF), haptoglobin (HP), ceruloplasmin (CP), serum amyloid A (SAA), alpha 1-acid glycoprotein (AGP) and alpha 2-HS-glycoprotein (AHSG) during the acute-phase reaction in C57B1 mice. The acute-phase reaction was induced by intraperitoneal injections of bacterial lipopolysaccharide (LPS). During the acute-phase reaction, genes encoding CP, SAA, AGP, and HP demonstrate unique extrahepatic tissue specific patterns of expression in kidney, spleen, thymus, heart, brain, lung, testis, and epididymis. Different temporal patterns of HP gene expression also were observed in lung and thymus after induction by LPS. The function of extrahepatic synthesis of plasma proteins is not yet understood; however, a local provision of specific plasma proteins in mammalian tissues may offer the host a source of functionally important proteins during periods of stress.

Interleukin 2 mediates stimulation of complement C3 biosynthesis in human proximal tubular epithelial cells

Previous reports have suggested the production of complement components C4, C2, and factor B by renal tissue. However, the cells involved in production of complement have not been identified. In this study metabolic labeling experiments demonstrated that human proximal tubular epithelial cells (PTEC) synthesize a 180-kD precursor of C3 that is secreted after proteolytic cleavage into a disulphide linked two-chain molecule as found in plasma. C3 present in culture supernatants of PTEC was functionally active, however, during the culture period there was a partial inactivation of the C3 molecule as assessed by hemolytic titration. Recombinant IL-2 enhances the rate of C3 synthesis in a dose-dependent manner reaching maximal stimulation at doses of 200-400 U/ml IL-2. Northern blot analysis demonstrated a 5.2-kb C3 mRNA species present in PTEC that was increased within 24 h of IL-2 treatment. IL-2-induced enhancement of C3 production by PTEC could be neutralized with specific antibodies to IL-2. This study demonstrates that C3 synthesis in PTEC is upregulated by IL-2, the major cytokine produced by activated T cells.

Interleukin-6 and the acute phase response

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Host defense against infections and inflammations: role of the multifunctional IL-6/IFN-beta 2 cytokine

IL-6/IFN-beta 2 appears to be one of the important mediators of the response to viral and bacterial infections and to shock. The biological effects now associated with IL-6/IFN-beta 2 include: stimulation of immunoglobulin secretion by mature B lymphocytes (BSF-2 activity), growth stimulation of plasmacytomas and hybridomas (HGF activity), activation of T cells, stimulation of hepatic acute phase protein synthesis (HSF activity), stimulation of hematopoiesis, cell differentiation (DIF activity), inhibition of tumor cell growth (AP activity) and other IFN-like effects. As a typical cytokine, IL-6/IFN-beta 2 is secreted by many cell types and acts in various combinations with other interleukins and interferons.