Metformin improves CD8+ T cell responses and parasitemia control via macrophage modulation during Trypanosoma cruzi infection.

The immune response to Trypanosoma cruzi infection relies on robust inflammatory activation of macrophages and proper CD8+ T cells function to control parasite replication. However, an exacerbated respiratory burst from macrophages can damage tissues where parasites reside, such as the heart and liver. Subsequent fibrotic repair in the heart contributes to cardiomyopathy in patients with chronic Chagas disease and in mouse models. Additionally, respiratory burst metabolites are implicated in the impairment of CD8+ T cell responses. While excessive reactive oxygen species (ROS) production is associated with increased differentiation of Foxp3+ regulatory T cells (Tregs), T cell receptor (TCR) nitration occurs in the presence of high extracellular nitric oxide (NO) levels. Both mechanisms contribute to CD8+ T cell suppression during T. cruzi infection. In this study, we use metformin (Metf) to balance parasite control and immune-mediated tissue damage by modulating macrophage activation. We found that Metf ex vivo treatment in peritoneal macrophages (PEMs) from acutely infected mice led to reduced iNOS expression, decreased NO production and lower secretion of IL-1β, TNF and IL-6. However, IL-12 levels increased and CD8+ T cells co-cultured with these PEMs showed enhanced proliferation and IFN-γ production. In vivo, Metf-treated infected mice exhibited lower parasitemia and improved CD8+ T cell functionality, potentially linked to reduced TCR nitration and decreased Treg frequencies in the peritoneum, as well as reduced cardiac inflammation. These findings provide new insights into the inflammatory modulation exerted by Metf and its potential impact on CD8+ T cell response and Chagas disease outcome.