Brucella abortus RNA diminishes IFN-gamma-induced MHC-I molecules in different line regular and tumor cells

Abstract

Brucella abortus (Ba) is an intracellular pathogen capable of surviving inside macrophages. Since the disease is presented in multiple forms, many different cells are susceptible to be infected by Ba. We have previously demonstrated that Ba RNA diminishes the IFN-ɤ-induced MHC-I surface expression in human macrophages, retaining them within the Golgi Apparatus (GA). However, we acknowledged whether this event could be triggered in other cells able to be infected with Ba. So, we stimulated the lung epithelium cell line (Calu-6) and the endothelial microvasculature cell line (HMEC) with different doses of Ba RNA in the presence of IFN-ɤ. MHC-I expression was assessed by flow cytometry. Ba RNA (10 ug/ml) diminished the IFN-ɤ-induced MHC-I surface expression (p<0.05) in both cell lines. Next, by confocal microscopy, we observed colocalization of MHC-I and GA marker GM130 in CALU-6 cells treated for 48h, although to a lesser extent than in human macrophages (p<0.05). Conversely to what we expected, supernatants from Calu-6-Ba RNA-treated cells had higher IL-8 production compared to those from untreated cells (p<0.05). In addition, a decrease in MHC-I on the surface could be accompanied by an activation of Natural Killer (NK) cells. These cells are key for the defense against multiple tumors. Therefore, a question of great importance is: what is the relevance of MHC-I modulation in the context of other pathologies in which NK response is critical? For this we started by stimulating the human glioblastoma cells (U251) with different doses of Ba RNA in the presence of IFN-ɤ. MHC-I expression was assessed by flow cytometry. Ba RNA diminished the IFN-ɤ-induced MHC-I surface expression (p<0.05) in U251. Together these results show that Ba could persist successfully within the host, remaining unnoticed and evading CD8+ T cell surveillance. On the other hand, the decrease in MHC-I could enhance the subsequent cytotoxic response against multiple tumors.