The role of nitric oxide (NO) in parasitic infections

Nitric oxide (NO) has been shown to play a crucial role in various physiological and pathological conditions. NO plays a role in the immunoregulation and it is implicated in the host non-specific defence in a variety of infections. Abundant evidence indicates that NO contributes to the host defence function of macrophages. High levels of NO are mediated by up-regulated expression of the iNOS gene in response to the activating signals, in particular to the secretion of pro-inflammatory cytokines (IFN-gamma, TNF-alpha, IL-1, IL-2) by Thl cells. In this review, the role of NO during a number of parasitic infections has been summarized. Up to now, enhanced levels of NO production and expression of iNOS gene have been described in such infective diseases as malaria, toxoplasmosis, leishmaniosis, trypanosomosis and schistosomosis. During these infections, the preferential production of pro-inflammatory cytokines predisposes to the increased synthesis of NO, which mediates host protection through either direct parasite killing or by limiting parasite growth. The evidence presented in this review supports the conclusion that NO plays an important role in the majority of parasitic infections.