Local Complement Production Research Articles

Cytokine-regulated production of the major histocompatibility complex class-III-encoded complement proteins factor B and C4 by human glomerular mesangial cells

Local production of complement within normal or diseased kidneys could be of importance during local inflammatory reactions. In the present study, we demonstrate that human MCs are able to synthesize the MHC class-III-encoded complement proteins factor B and C4 in vitro. This synthesis is strongly upregulated following stimulation with cytokine-containing supernatants of activated peripheral blood mononuclear cells. All primary cell lines tested so far are able to synthesize factor B and C4 after stimulation. To determine more specifically whether defined cytokines are able to enhance factor B and C4 complement production, MCs were stimulated with IL-1α, IFN-γ, and TNF-α. Factor B synthesis was increased in a dose-dependent fashion by IL-lα, TNF-α, and IFN-γ, whereas C4 synthesis was only upregulated by IFN-γ. Furthermore, factor B synthesis was upregulated after stimulation with IFN-α, -β, and -γ and C4 synthesis only by IFN-γ. The synthesis of factor B and C4 was inhibited by cycloheximide, suggesting de novo protein synthesis. The cytoplasmic localization of both components was shown by immunofluorescence studies. Northern and dot blot analysis revealed induction of factor B and C4 mRNA after stimulation with cytokines.

Silica induced suppression of the production of third and fifth components of the complement system by human lung cells in vitro.

Although investigations to date have demonstrated the ability of the monocyte/macrophage to synthesize complement components, only a limited number of studies on complement synthesis by nonhepatic tissue cells have been reported. To begin to fill this gap in our knowledge we have recently evaluated the ability of lung tissue cells to synthesize and secrete various complement components in vitro. Using 35S-methionine incorporation and immunoprecipitation techniques we have previously demonstrated the ability human lung type II pneumocytes (A549) and human lung fibroblasts (WI-38), to synthesize and secrete a variety of both early and terminal complement components, as well as several regulatory proteins including Clr, Cls, C4, C3, C5, C6, C7, C8, C9, Factor B, Factor H, Factor I and Cls inactivator. Our present studies demonstrate the capability of silica to regulate complement component production by A549 cells, but not complement component production by WI-38 cells. Specifically, using sensitive ELISAs we demonstrated that a non-toxic dose of silica had the capability to suppress the production of both C3 and C5 by A549 pneumocytes by 40-50 percent, but had no effect on C3 or C5 synthesis by WI-38 fibroblasts. Additionally, using 35S-methionine incorporation and TCA precipitation techniques, we demonstrated that suppression of C3 and C5 production by silica treated A549 pneumocytes was not a result of suppression of total protein synthesis. These studies demonstrate that silica, which has been implicated in pulmonary diseases, has the capability to regulate local complement production by lung tissue cells in vitro. In vivo, this suppression of complement production by the type II pneumocytes could alter the local tissue reservoir of complement components during infection and pulmonary injury, thus resulting in depressed pulmonary host defense.

Synthesis of complement by guinea pig bronchoalveolar macrophages. Effect of acute and chronic infection with Pseudomonas aeruginosa.

In order to assess the potential role of local production of complement in pulmonary host defenses against bacterial infection, this aspect of bronchoalveolar macrophage function was studied in guinea pigs challenged with Pseudomonas aeruginosa in an acute and chronic infection model. Acute infection resulted in an increase in bronchoalveolar macrophage cell number and an increase in synthesis and secretion rates for the second (C2) and fourth (C4) complement components per macrophage. Manipulation of the airway without introduction of Pseudomonas also increased synthesis of both C2 and C4 when studied 60 h after control solutions were administered. Pseudomonas aeruginosa delivered in agar beads to induce chronic inflammation resulted in specific stimulation of C2 and C4 synthesis at 2 wk and to a lesser extent at 4 wk postchallenge. This increase in local complement synthesis by bronchoalveolar macrophages, in addition to enhancing the local inflammatory response, may serve to facilitate recruitment of intravascular cellular and humoral mediators of host defense against bacterial infection.

Biosynthesis of complement components in chronically inflamed gingiva.

The biosynthesis of the third and fifth components of complement in chronically inflamed gingiva is demonstrated. The technique utilized in these studies was an immunochemical detection of 14C‐labeled amino acid incorporated protein from gingival explant cultures. C3 and C5 synthesis was detected in 8 of 10 individuals with periodontal disease, while no evidence of synthesis was noted in 5 control subjects. The results indicate an even greater consumption of complement occurs in periodontal disease than has been predicted previously using serum as the sole source of complement. The local production of complement could play a role in modulating the inflammatory response in the gingiva.