Immunomodulation of bone marrow-derived dendritic cells during endotoxin- and bacterial sonicate-induced tolerance

As important members of the innate immune response and conduits for induction of cell-mediated immunity, dendritic cells (DCs) have emerged as integral to understanding the immune response to pathogens. Due to their role in inflammation, ability to stimulate naïve T cells, and widespread presence in the body, the study of their physiological response is key to conceptualize immune function and pathology. While dendritic cells have been shown to influence tolerance in T cell populations, there is a dearth of investigation as to the development of tolerance among DCs themselves. In cells closely related to DCs such as macrophages and monocytes, prior exposure to minute amounts of endotoxin (LPS) can lead to a refractory period where subsequent exposure to higher doses fails to induce an inflammatory response. This study aims to characterize the immunomodulatory response of bone marrowderived dendritic cells in instances of endotoxin tolerance, as well as tolerance induced by bacterial sonicate containing multiple stimulatory ligands. Murine bone marrow-derived dendritic cells (BM-DCs) were harvested and cultured (tolerized) with 5 ng/ml LPS or 2 μg/ml of either E. coli or H. pylori strain SS1 sonicate, thoroughly washed, rested, and stimulated with the same component at a higher dose, physiologically mimicking a low-dose primary exposure and a larger secondary exposure. Along with a significant drop in TNF-α and IL-12p70 production, tolerized BM-DCs exhibited increased IL-10 expression. Tolerization and reexposure to H. pylori SS1 sonicate uniquely showed a decreased expression of IL-6 in tolerized BM-DCs. Furthermore, interleukin 1 receptor-associate kinase-M (IRAK-M), a negative regulator of TLR signaling through NF-κB, showed increased intracellular expression during endotoxin tolerance when its transcript was tested with qPCR and protein expression was