Recombinant SSP4 protein from Trypanosoma cruzi amastigotes regulates nitric oxide production by macrophages.

Acute infection with Trypanosoma cruzi is characterized by immunosuppression mediated by T cells and macrophages (Mphis). Nitric oxide (NO) production during the initial phase of acute infection might participate in the clearance of parasites by Mphis, whereas its overproduction during the late phase of acute infection would account for the immunosuppression observed. Trypanosoma cruzi molecules that might regulate the host responses have not been fully identified. Here, we demonstrate that active immunization with MBP::SSP4, a recombinant protein derived from a surface antigen specific of T. cruzi amastigotes (TcSSP4), was able to stimulate Ab production (IgG1, IgG2a, and IgG2b). On the other hand, MBP::SSP4 was able to stimulate NO production by peritoneal Mphis from BALB/c mice and Mphis from the J774 cell line. This effect was also observed at the level of inducible nitric oxide synthase (iNOS) detected by Western Blot. Furthermore, MBP::SSP4 was also shown to induce the expression of IL-1alpha, IL-6, IL-12, IFN-gamma, and TNF-alpha in normal animals, and IL-10 in immunized animals. In addition the protein MBP::SSP4 was able to bind to the surface of PMphis and J774 Mphis. These results suggest that TcSSP4 could modulate Mphi NO production and this may represent a mechanism participating in the immunoregulatory processes during Chagas' disease.