Hemoglobin binding activity and hemoglobin-binding protein of Prevotella nigrescens

Neutrophils in the periodontium: Interactions with pathogens and roles in tissue homeostasis and inflammation

Neutrophils are of key importance in periodontal health and disease. In their absence or when they are functionally defective, as occurs in certain congenital disorders, affected individuals develop severe forms of periodontitis in early age. These observations imply that the presence of immune-competent neutrophils is essential to homeostasis. However, the presence of supernumerary or hyper-responsive neutrophils, either because of systemic priming or innate immune training, leads to imbalanced host-microbe interactions in the periodontium that culminate in dysbiosis and inflammatory tissue breakdown. These disease-provoking imbalanced interactions are further exacerbated by periodontal pathogens capable of subverting neutrophil responses to their microbial community's benefit and the host's detriment. This review attempts a synthesis of these findings for an integrated view of the neutrophils' ambivalent role in periodontal disease and, moreover, discusses how some of these concepts underpin the development of novel therapeutic approaches to treat periodontal disease.

The Hunger Games: Aggregatibacter actinomycetemcomitans Exploits Human Neutrophils As an Epinephrine Source for Survival

Aggregatibacter actinomycetemcomitans is a gram-negative facultative anaerobe and an opportunistic oral pathogen, strongly associated with periodontitis and other inflammatory diseases. Periodontitis is a chronic inflammation of the periodontium resulting from the inflammatory response of the host towards the dysbiotic microbial community present at the gingival crevice. Previously, our group identified catecholamines and iron as the signals that activate the QseBC two-component system in A. actinomycetemcomitans, necessary for the organism to acquire iron as a nutrient to survive in the anaerobic environment. However, the source of catecholamines has not been identified. It has been reported that mouse neutrophils can release catecholamines. In periodontitis, large infiltration of neutrophils is found at the subgingival pocket; hence, we wanted to test the hypothesis that A. actinomycetemcomitans exploits human neutrophils as a source for catecholamines. In the present study, we showed that human neutrophils synthesize, store, and release epinephrine, one of the three main types of catecholamines. Human neutrophil challenge with A. actinomycetemcomitans induced exocytosis of neutrophil granule subtypes: secretory vesicles, specific granules, gelatinase granules, and azurophilic granules. In addition, by selectively inhibiting granule exocytosis, we present the first evidence that epinephrine is stored in azurophilic granules. Using QseC mutants, we showed that the periplasmic domain of the QseC sensor kinase is required for the interaction between A. actinomycetemcomitans and epinephrine. Finally, epinephrine-containing supernatants collected from human neutrophils promoted A. actinomycetemcomitans growth and induced the expression of the qseBC operon under anaerobic conditions. Based on our findings, we propose that A. actinomycetemcomitans promotes azurophilic granule exocytosis by neutrophils as an epinephrine source to promote bacterial survival.