TNF and systemic inflammatory response syndrome: Although the mechanisms involved in neutrophil migration are not fully understood, it is known that high levels of circulating cytokines/chemokines (including TNF-α and IL-1β) modulate the failure of neutrophil migration during SIRS, by releasing nitric oxide (NO), mainly produced by NO inducible synthase (iNOS) (Farias Benjamim et al., 2002; Mestriner et al., 2007).