Complement Subcomponent C1q Modulation of TNF‐α Binding to L929 Cells for Enhanced TNF‐Mediated Cytotoxicity

Abstract

Complement subcomponent C1q has been recently implicated in the modulation of autocrine binding of TNF‐α to murine macrophages for induction of nitric oxide synthase. In the present study, the putative role of C1q in increasing TNF‐α binding to L929 cells to mediate cytotoxicity was explored. TNF‐sensitive L929 cells (L929‐S) had higher total endogenous cellular and surface C1q levels and bound correspondingly more phycoerythrin‐labelled rTNF‐α (PE‐TNF) than did a TNF‐resistant L929 variant (L929‐R). Pretreatment of L929‐S with soluble C1q increased their sensitivity to TNF‐mediated cytotoxicity coincident with increased binding of PE‐TNF, but similar treatment of L929‐R had no effect. Pretreatment of L929‐S with an inhibitor of C1q secretion, 3,4 dehydro‐D,L‐proline (DHP), resulted in a decrease in their TNF‐mediated cytotoxicity, as well as reduced binding of PE‐TNF. Subsequent exposure of DHP‐treated L929‐S with exogenous soluble C1q restored their TNF‐mediated cytotoxicity and binding of PE‐TNF. These results provide evidence for the modulation of TNF‐α binding to TNF sensitive tumour targets L929 by either endogenously synthesized or exogenously added C1q to promote TNF‐mediated cytotoxicity by mechanisms which remain to be elucidated.

Cyclosporin A Suppresses the Induction of Nitric Oxide Synthesis in Interferon‐γ‐Treated L929 Fibroblasts

“…Induction of NO synthesis by IFN‐γ in L929 cells was previously reported by us [15] and it is consistent with results describing NO production in LPS‐stimulated and cytokine (IFN‐γ, IL‐1, TNF‐α)‐stimulated rodent primary fibroblasts [11]. It has also been shown that L929 cells produce NO during co‐cultivation with macrophages or treatment with TNF‐α, IFN‐α/β and LPS [18, 19]. IFN‐γ‐induced NO synthesis in L929 cells was mediated via an iNOS‐dependent l ‐arginine‐NO pathway, since it was abolished by the specific iNOS inhibitor AG.…”

“…In addition, the question of whether CsA can down‐regulate IL‐1 synthesis in L929 fibroblasts becomes irrelevant in light of the finding that even 100 ng/ml IL‐1Ra could not reduce IFN‐γ‐mediated NO production in these cells (unpublished observation). Recently, other members of the interferon family, IFN‐α/β have also been shown to activate NO synthesis in L929 cells [19]. Furthermore, their ability to secrete IFN‐β has been confirmed [25].…”

Induction of tumoricidal activity in mouse peritoneal macrophages by ginseng polysaccharide

“…The activation process includes the generation of cytokines including interleukin-1 (IL-1), tumor necrosis factor (TNF)-␣, interleukin-6 (IL-6) and interleukin-12 (IL-12), and they are directly involved in the macrophage-mediated tumor cell killing. Furthermore, cytokines such as TNF-␣, IL-1, and IFN-␥ have been found to modulate macrophage functions by producing synergistic effects with other agents, inducing the release of cytotoxic molecules from macrophages [6][7][8]. Peritoneal macrophages can be stimulated by a variety of agents, such as IFN-␥, lipopolysaccharides (LPS), and other microbial products [9][10][11][12][13].…”

Investigation of the functional characteristics of antibodies to therapeutic anti-human tumor necrosis factor alpha monoclonal antibody

“…Because the control serum also demonstrated a cytotoxic activity, we considered that another TNF-unrelated factor present in sera seemed to be participating in cytotoxic effect on L929 cells. It was reported that pre-treatment of TNFsensitive L929 cells with soluble C1q increased their sensitivity to TNF-mediated cytotoxicity [24]. Hence, complement proteins might be responsible for such an activity.…”