Membrane cofactor protein (MCP, CD46) is an integral protein that serves as a cofactor for factor I in inactivating C3b/C4b deposited on the same cell membrane as C3bi/C4c+C4d. This C3b/C4b inactivation is closely associated with self-protection of host cells from autologous complement attack. We have studied the distribution and properties of MCP in the normal human kidney by immunohistochemical and immunoblotting methods using monoclonal antibodies against MCP. MCP was predominantly expressed on the juxtaglomerular apparatus. Glomerular capillary walls, mesangial areas, and tubulus were also MCP positive. Glomerulus MCP was composed of two major bands of 45-65 kDa, which were similar to those of lymphocyte MCP. The proportion of the high and low molecular weight components in glomerulus MCP, however, was considerably different from that of lymphocyte MCP among the individual samples tested. Glomerular epithelial cells and mesangial cells from an individual having equal amounts of high and low molecular weight components in the lymphocytes were cultured separately and the properties of their MCP investigated. MCP in the mesangial cells and glomerular epithelial cells showed profiles in which the upper band was predominant. The results may explain the unique distribution of the high and low molecular weight forms in the glomerulus. These forms of MCP together with factor I were all capable of inactivating C3b to C3bi. Message analysis suggested that glomerular epithelial cells and mesangial cells synthesized a single species of mRNA of 4.2 kb from which the polymorphic MCP species were generated. Flow cytometric analysis suggested that MCP was minimal in mesangial cells. These results, taken together with the previous reports on the distribution of other complement regulatory proteins, infer that the distribution profile of MCP is rather similar to that of DAF but differs from those of CD59 and CR1 in the normal human kidney; this may reflect the differences between their roles or functional properties in renal tissue.

The administration of FK506 or cyclosporin A (CyA) to animals and humans induces a decrease in glomerular filtration rate and renal plasma flow and an increase in renal vascular resistance. Endothelins (ET-1), very powerful renal vasoconstrictors, are involved in CyA-related alteration in renal haemodynamics. In this study we sought to determine whether FK506 and CyA had a stimulatory effect on endothelin secretion by cultured kidney cells (tubular and mesangial cells) and whether this stimulatory effect coincided with an increase in ET-1 serum level in FK506-and CyA-treated rats. FK506 concentrations of 1, 0.1, O.Ql and 0.001j.tM significantly stimulated ET-1 secretion by cultured tubular and mesangial cells. CyA at 10, 1, 0.1 and 0.01j.tM also exerted an enhancing effect on ET-1 secretion in cultured tubular cells whereas CyA only at 10 and lj.tM had a stimulatory effect on ET-1 secretion by human mesangial cells. We observed that the concentrations of Cy A that induced the most substantial enhancing effect were 10 or 100 times higher than those required for FK506 to produce the same effect. The concentrations of FK506 or CyA which induced ET-1 secretion by tubular cells and kidney cells were not cytolytic as assessed by N-acetyl-~-D-glucos aminidase (NAG) release and lactic dehydrogenase (LDH) release. FK506 or CyA treatment at toxic doses induced an increase in serum level of ET-1 in treated rats. We conclude that FK506 and CyA induced an increase in the synthesis of endothelin in the kidney which may explain the increase in circulating ET-1. This stimulatory effect may contribute to the genesis of haemodynamic preturbations associated with FK506 and Cy A. FK506 is a newly developed immunosuppressive drug which has been used successfully in clinical transplanta-Offprint requests to: Michio Ishibashi. M.D.tion [4,13]. Among its recognized side effects, nephrotoxicity is the most prominent [3]. Its molecular structure is unrelated to cyclosporin A (CyA), but both agents have similar pharmacological effects and may possibly have the same toxicity. It has been reported that FK506 decreases the glomerular filtration rate (GFR) and renal plasma flow (RFP) and increases renal vascular resistance in humans [19] and in rats [7] treated with FK506. These reversible haemodynamic perturbations that have also been observed in CyA nephrotoxicity, have been linked to the renin angiotensin, adrenergic systems, and thromboxane A2 [8,11]. Endothelin (ET), a peptide isolated from supernatants of cultured porcine aortic endothelial cells is a very powerful renal vasoconstrictor [20]. ET is ten times more potent than angiotensin II, vasopressin, or neuropeptide Y, making it the most potent endogenous vasoacth:e substance known [20]. ET appears to have a pivotal role in the pathophysiology of Cy A-induced acute renal vasoconstriction and glomerular dysfunction [5]. Renal cell lines and mesangial cells physiologically express mRNA for endothelin and secrete this peptide in the supernatant [14,21]. In this study we demonstrated that...

Interleukin-6 (IL-6) has been extensively studied in mesangial cells but little is known about the expression of this cytokine and its receptor in glomerular epithelial cells (GEC). IL-6 was detected in the culture supernatants of human GEC and its production was enhanced in time and dose dependent manner by lipopolysaccharide (LPS), interleukin-1 beta (IL-1 beta) and tumour necrosis alpha (TNF-alpha). Quiescent, serum-starved GEC did not express clearly IL-6 mRNA. Stimulation of cells with LPS, TNF-alpha or IL-1 beta resulted in an increase of detectable IL-6 mRNA. Interestingly, it was found that IL-6 induced its own mRNA attesting that this cytokine was secreted in autocrine fashion by GEC. GEC expressed IL-6 receptor (IL-6R) as demonstrated directly by the existence of IL-6R mRNA detected by northern blotting. Stimulation of GEC by pro-inflammatory mediators such as LPS increased the expression of IL-6R mRNA. The soluble form of IL-6 receptor (sIL-6R) was not detectable in the culture supernatants harvested from untreated or cytokine-treated cells. We investigated further, whether IL-6 may influence growth of cultured GEC. Incubation of GEC with recombinant (r) IL-6 resulted in a dose dependent increase in 3H thymidine incorporation indicating that IL-6 acts as an autocrine growth factor for GEC. We conclude that GEC are a potent source of IL-6, the local excessive expression of IL-6 and its receptor may play a substantive role in the regulation of processes which appear critical to the initiation of progressive glomerular disease such as cell proliferation.

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