The Emerging Oral Pathogen, Filifactor Alocis, Extends the Functional Lifespan of Human Neutrophils

Periodontitis is a chronic inflammatory infectious disease that affects the integrity of tooth-supporting tissues and has adverse systemic consequences. Advances in sequencing technologies have uncovered organisms that are exclusively found in high numbers in periodontal lesions, such as the gram-positive anaerobic rod, Filifactor alocis. F. alocis can manipulate neutrophil effector functions, which allows the organism to survive within these granulocytes. Several neutrophil functions have been tested in the context of F. alocis challenge, but the effect of the organism on neutrophil apoptosis is still unknown. RNA sequencing of human neutrophils challenged with F. alocis showed that apoptosis pathways were differentially regulated. Compared to media-cultured controls, F. alocis-challenged neutrophils maintain their nuclear morphology, do not stain for Annexin V or 7-AAD, and have decreased DNA fragmentation. Inhibition of apoptosis by F. alocis involved reduced caspase-3, -8, and - 9 activation and upregulation of important anti-apoptotic proteins. Prolonged lifespan was dependent on contact through TLR2/6, and F. alocis-challenged neutrophils retained their functional capacity to induce inflammation for longer timepoints. This is the first in-depth characterization of neutrophil apoptotic programs in response to an oral pathogen and provides key information on how bacteria manipulate immune cell mechanisms to maintain a dysregulated inflammatory response.