In vitro and in vivo canine mononuclear cell production of tumor necrosis factor induced by muramyl peptides and lipopolysaccharide

Abstract

Tumor necrosis factor (TNF) is a potent mediator of tumor cell killing by activated monocytes and macrophages. We measured TNF activity induced by muramyl peptides and lipopolysaccharide (LPS) in normal dogs. Canine adherent mononuclear cells were isolated and cultured in either medium alone or medium containing muramyl dipeptide (MDP) or MDP plus LPS. After 18 h, culture supernatants were collected and assayed for TNF activity. Sera from dogs injected with liposome-encapsulated muramyl tripeptide-phosphatidylethanolamine (L-MTP-PE) were also evaluated for TNF activity. TNF activity both in supernatants and in sera was detected in a 18 h WEHI-164 cell cytotoxicity assay and was confirmed by a monoclonal antibody directed against recombinant human TNF-α. Results showed a significant increase in TNF activity from mononuclear cells exposed to MDP or MDP plus LPS of 20% and 88%, respectively; P<0.0005. Serum TNF activity rapidly increased within 2–3 h post L-MTP-PE injection and subsequently declined to pretreatment level at 4 h post administration. This study demonstrates that MDP±LPS can stimulate canine adherent mononuclear cells to release TNF and intravenous injection of L-MTP-PE is capable of rendering the in vivo release of TNF in normal dogs.