Lymphoid Tissue-Residentalcaligenesestablish An Intracellular Symbiotic Environment By Creating A Unique Energy Shift In Dendritic Cells

Lymphoid-tissue-resident commensal bacteria (LRCs), includingAlcaligenes faecalis, are present in intestinal lymphoid tissue including the Peyer's patches (PPs) of mammals and modulate the host immune system. Although LRCs can colonize within dendritic cells (DCs), the mechanisms through which LRCs persist in DCs and the symbiotic relationships between LRCs and DCs remain to be investigated. Here, we show an intracellular symbiotic system in which the LRCAlcaligenescreates a unique energy shift in DCs. Whereas DCs showed low mitochondrial respiration when they were co-cultured withEscherichia coli, DCs carryingA. faecalismaintained increased mitochondrial respiration. Furthermore,E. coliinduced apoptosis of DCs butA. faecalisdid not. Regarding an underlying mechanism,A. faecalis-unlikeE. coli-did not induce intracellular nitric oxide (NO) production in DCs due to the low activity of its lipopolysaccharide (LPS). Therefore,A. faecalis, an example of LRCs, may persist within intestinal lymphoid tissue because they elicit little NO production in DCs. In addition, the symbiotic DCs exhibit characteristic physiologic changes, including a low rate of apoptosis and increased mitochondrial respiration.