Role of reactive nitrogen species in neuronal cell damage during intestinal schistosomiasis

Free radicals are known to be involved in the host reaction during Schistosoma mansoni-induced inflammation in the liver and the intestine. In the present study, the influence of reactive nitrogen species (RNS) on the enteric neurons of infected ileum of mice was investigated. Cryosections and whole-mounts of the ileum of control, and 8- and 15-week-infected mice were processed for immunohistochemical localization of 3-nitrotyrosine, a biomarker of RNS, and of active caspase-3, a key executioner of apoptosis. An antibody directed against protein gene product 9.5 or S100 protein was used as a marker for neurons or enteroglial cells. In infected mice, but not in control animals, 3-nitrotyrosine was detected in parasite eggs and, as revealed by double immunolabelling, in some neuronal and enteroglial cells. Quantitative analysis of whole-mounts showed that the percentage of 3-nitrotyrosine-immunoreactive neurons significantly increased with time in both the submucous and myenteric plexus. Caspase-3 immunoreactivity was predominantly found in parasite eggs in infected mice. Immunoreactive enteric neurons were occasionally observed. The results indicate that inflammation-induced RNS are present in the ileum of S. mansoni-infected mice, and participate in the elimination of the schistosome eggs causing damage in a significant number of enteric neurons. However, neuronal cell death appears to be a rare phenomenon in the schistosome-infected mouse ileum.