Oestrus ovis (Diptera : Oestridae): effects of larval excretory/secretory products on nitric oxide production by murine RAW 264 center dot 7 macrophages

Larvae of Oestrus ovis (Insecta: Diptera: Oestridae) are common parasites o f nasal and sinus cavities of sheep and goats. Previous studies revealed th at crude extracts of larvae modify NO synthesis by ovine monocyte derived m acrophages. The aim of this study was to investigate the larval excretory/s ecretory products effects on nitric oxide production by murine tumour macro phages RAW 264.7. Stimulation of RAW macrophages by excretory/secretory pro ducts of the three instars larvae (25 mug/ml) significantly increased nitri te concentrations in culture supernatants compared to negative and positive Escherichia coli lipopolysaccharide control. This effect was time and dose dependent. Nitrite production in culture supernatants was due to induction of isoform NOS-2 because both N-G monomethyl l-arginine (100 mum) and dexa methasone (20 mum) inhibited, by 60 and 50%, respectively, nitrite accumula tion in culture supernatants. First steps of purification, by ion exchange chromatography, indicated that one protein of 29 kDa was able to induce NO synthesis by macrophages. Further studies are needed for a better character ization of these molecule and to investigate their immunogenicity for a vac cine approach.