Human neutrophils and oral microbiota: a constant tug‐of‐war between a harmonious and a discordant coexistence

Abstract

Summary Neutrophils are a major component of the innate host response, and the outcome of the interaction between the oral microbiota and neutrophils is a key determinant of oral health status. The composition of the oral microbiome is very complex and different in health and disease. Neutrophils are constantly recruited to the oral cavity, and their protective role is highlighted in cases where their number or functional responses are impeded, resulting in different forms of periodontal disease. Periodontitis, one of the more severe and irreversible forms of periodontal disease, is a microbial-induced chronic inflammatory disease that affects the gingival tissues supporting the tooth. This chronic inflammatory disease is the result of a shift of the oral bacterial symbiotic community to a dysbiotic more complex community. Chronic inflammatory infectious diseases such as periodontitis can occur because the pathogens are able to evade or disable the innate immune system. In this review, we discuss how human neutrophils interact with both the symbiotic and the dysbiotic oral community; an understanding of which is essential to increase our knowledge of the periodontal disease process.

Neutrophil Role in Periodontal Disease

“…Even though the presence of neutrophils is necessary to control infections, plenty of neutrophils on a site of infection is not always protective. In fact, neutrophil numbers in inlamed periodontal tissues correlate with the severity of the lesions [37], and tissue destruction seems to be a collateral damage of hyperactive neutrophils [38].…”

“…Our general idea is that infectious diseases are caused by the action of a single foreign pathogen. However, periodontitis is originated by the complex association and interaction of a diverse polymicrobial community [37,51,55]. Data obtained from oral bioilm studies using checkerboard DNA-DNA techniques link the diferent stages of the disease to a speciic bacterial group or complex with the presence of the triad of bacteria composed by P. gingivalis, T. forsythia, and T. denticola, which are strongly associated with increased severity of periodontitis [56].…”

Characterization of Filifactor alocis and its immune evasion strategies employed against human neutrophils.

“…Neutrophils will be present in health, producing a low-level inflammatory state, stimulated through the presence of resident oral microbiota, where they serve as patrolling agents ready to respond if needed, until they will undergo eventual cell apoptosis and clearance by macrophages (184)(185)(186). In the inflamed periodontal tissue, chemotactic factors such as IL-8, as well as bacterial derived products, fMLF, will be abundant and guide neutrophils from the blood vessels through the gingival tissue towards the periodontal pocket (179,187,188).…”

“…In the context of periodontal disease, neutrophils are impaired in their ability to perform chemotaxis, which impacts their migration to the site of bacterial presence in the oral cavity, allowing for bacterial persistence and survival in the host (184,189). Additionally, these neutrophils are maintained in a 'primed' activation state both in the oral cavity and in the blood stream, which could have further implications in the association of oral disease with the development of other chronic inflammatory diseases like atherosclerosis, diabetes, and rheumatoid arthritis (184).…”

“…Additionally, these neutrophils are maintained in a 'primed' activation state both in the oral cavity and in the blood stream, which could have further implications in the association of oral disease with the development of other chronic inflammatory diseases like atherosclerosis, diabetes, and rheumatoid arthritis (184). Priming agents (e.g.…”