IN-VITRO AND IN-VIVO PRODUCTION OF INTERLEUKIN-6 INDUCED BY MURAMYL PEPTIDES AND LIPOPOLYSACCHARIDE IN NORMAL DOGS

Interleukin-6 (IL-6) is a multifactorial cytokine produced by many cel ls including monocytes and macrophages in the immune-stimulated host. We measured IL-6 activity induced by muramyl dipeptide (MDP) and lipop olysaccharide (LPS) in vitro and by liposome-encapsulated muramyl trip eptide-phosphatidylethanolamine (L-MTP-PE) in vivo in normal dogs. Adh erent mononuclear cells were cultured with MDP, LPS or MDP plus LPS fo r various time periods. After incubation, culture supernatants were co llected and assayed for IL-6 activity. Sera from dogs following L-MTP- PE administration were also evaluated for IL-6 activity. IL-6 activity both in supernatants and sera was measured using a 7TD1 bioassay. Sig nificantly elevated IL-6 activity could be measured as early as 2 hour s after mononuclear cells were exposed to MDP, LPS, or MDP plus LPS IL -6 activity induced by LPS was greater than that induced by MDP, and t he combination of MDP and LPS induced the greatest increase in IL-6 ac tivity. Serum IL-6 activity was elevated within 3 to 4 hours post L-MT P-PE administration and subsequently declined to pretreatment level at 24 hours post injection. Neutralization of supernatant and serum IL-6 activity was not achieved with goat or rabbit anti-recombinant human IL-6 polyclonal antibody. This study demonstrates that MDP and LPS, al one and in combination, can induce enhanced IL-6 activity of canine ad herent mononuclear cells in vitro, and that intravenous injection of L -MTP-PE is capable of eliciting increased IL-6 activity in vivo in nor mal dogs. These findings suggest that IL-6 may play an important role in the biologic response observed in canine cancer patients treated wi th L-MTP-PE.