RESUMO
Nitric oxide (NO) produced by inducible NO synthase (iNOS) mediates hypotension in endotoxemia. In this study, NO induction by a toxin-producing Streptococcus pyogenes isolate, H250, and by recombinant streptococcal pyrogenic exotoxin A (rSPEA) has been examined, both in vitro and in vivo. Streptococcal supernatants, but not rSPEA, induce production of nitrite by murine macrophages when both are coincubated with gamma interferon. Intraperitoneal injection of rSPEA did not cause significant production of NO. However, an elevated level of nitrate in serum was detected in a model of streptococcal fasciitis due to live H250. iNOS was localized to Kupffer cells, hepatocytes, and renal tubular cells by immunostaining. Administration of a NOS inhibitor, N(G)-monomethyl-L-arginine (L-NMMA), reduced peak concentrations of nitrate in serum but did not affect survival. NO is induced by H250, both in vitro and in vivo, mainly via SPEA-independent mechanisms. In this model, iNOS is expressed predominantly in the liver. Furthermore, in this model L-NMMA is not protective.
Assuntos
Exotoxinas/biossíntese , Exotoxinas/farmacologia , Óxido Nítrico/metabolismo , Óxido Nítrico/fisiologia , Proteínas Recombinantes/farmacologia , Sepse/metabolismo , Infecções Estreptocócicas/metabolismo , Streptococcus pyogenes , Animais , Células Cultivadas , Exotoxinas/genética , Imuno-Histoquímica , Interferon gama/farmacologia , Rim/metabolismo , Células de Kupffer/metabolismo , Fígado/metabolismo , Macrófagos Peritoneais/metabolismo , Masculino , Camundongos , Nitratos/análise , Nitratos/sangue , Óxido Nítrico Sintase/imunologia , Óxido Nítrico Sintase/metabolismo , Nitritos/metabolismo , ômega-N-Metilarginina/farmacologiaRESUMO
The role of streptococcal pyrogenic exotoxin A (SPEA) was evaluated in a murine model of fasciitis and multiorgan failure due to a toxigenic strain of Streptococcus pyogenes. Increased serum levels of SPEA at 15 and 21 h were associated with a survival time of <24 h. Levels of SPEA correlated with interleukin-6 levels. Immunostaining showed SPEA localized to renal and hepatic cells. Neutralizing rabbit antibody to SPEA was administered to mice challenged with S. pyogenes, but no effect on survival was observed. Vaccination of mice with recombinant SPEA enhanced mortality due to streptococcal infection, despite the development of neutralizing immunity to the toxin prior to infection. Hence, SPEA is produced systemically during S. pyogenes soft-tissue infection, and increased levels are associated with reduced survival. In this model, however, SPEA did not appear to play a dominant role in pathogenesis; passive immunization against SPEA was not protective, and active immunization enhanced mortality.
