Evidence for nitric oxide action on in vitro granuloma formation through pivotal changes in MIP-1alpha and IL-10 release in human schistosomiasis.

Nitric oxide (NO) has been implicated, both and paradoxically, as a pro- and anti-inflammatory agent in a wide range of circumstances. It is of common concern that NO can be either up- or downregulated by different inflammatory cytokines. Attempting to assess the contribution of NO to the granulomatous response, we used the in vitro granuloma (IVG) model which consists on a reaction of mononuclear cells around polyacrylamide beads conjugated to antigens. Our assays employed Schistosoma mansoni antigens and human peripheral blood mononuclear cells (PBMC) from schistosomiasis patients. Recently, we have described evidence for a regulatory role of NO, with the aid of an inhibitor of NO synthesis, L-NAME. The addition of L-NAME to IVG cultures elicited an increase on the granuloma formation index. Based on these data we decided to investigate the mechanisms involved in the effects of L-NAME-enhanced granuloma formation. Cytokines and chemokines are involved in inflammatory responses by, particularly the latter, inducing migration and adhesion of leukocytes, which led us on this search for their interactions with NO on granulomatous reaction. We evaluated the cytokine/chemokine-secreting profile of PBMC (treated and not treated with L-NAME) on the IVG reaction in order to investigate how NO could interfere on the release of these soluble mediators. Comparison of cell culture releasing amounts of IL-2, IL-10, TNFalpha, IFNgamma, MIP-1alpha, MCP-1, and RANTES demonstrated that MIP-1alpha had increased levels when NO production was blocked with L-NAME, whereas IL-10 secretion decreased in presence of L-NAME. The other tested cytokines (IL-2, TNFalpha, and IFNgamma) and chemokines (MCP-1 and RANTES) showed no significant differences between the presence or absence of L-NAME. Results obtained in this work suggest that inhibition of NO production could upregulate the IVG reaction on human schistosomiasis through changes in the cytokine/chemokine profile released by PBMC. The mechanisms involved may lead to a MIP-1alpha-increased and IL-10-decreased secretion under our experimental conditions, which could partly account for the previously ascribed IVG-exacerbating action of NO inhibition.