Extracellular products from virulent strain of Edwardsiella tarda stimulate mouse macrophages (RAW264.7) to produce nitric oxide (NO) and tumor necrosis factor (TNF)-alpha

Fish & Shellfish Immunology
Yajun WangKenji Hara

Abstract

We have previously found that high virulent strain (NUF251) of Edwardsiella tarda, but not low virulent strain (NUF194), was able to survive and multiply within Japanese flounder (Paralichthys olivaceus) peritoneal macrophages. Further studies demonstrated that NUF251 induced much higher levels of NO and TNF-alpha productions than NUF194 in both Japanese flounder peritoneal macrophages and mouse macrophage cell line RAW264.7. In this study, we examined the effects of extracellular products (ECP) from two strains of E. tarda on RAW264.7 cells in terms of the induction of NO and TNF-alpha. ECP from NUF251 stimulated RAW264.7 cells to induce NO production in a concentration-dependent manner. The activity of NUF251-ECP completely disappeared by heat-treatment (at 100 degrees C for 5 min), but it could not be removed by dialysis. Polymyxin B, an endotoxin inhibitor, had no effect on NUF251-ECP-induced NO production. These results suggest that active agents in NUF251-ECP responsible for NO induction may be heat-labile high molecular weight substances rather than the cell wall derived endotoxin like substances. Since NO synthase (NOS) inhibitor, l-NAME, suppressed NUF251-ECP-induced NO production, inducible NO synthase (iNOS) in RAW26...Continue Reading

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