Filifactor alocismodulates human neutrophil antimicrobial functional responses

Abstract

Filifactor alocis is a newly appreciated pathogen in periodontal diseases. Neutrophils are the predominant innate immune cell in the gingival crevice. In this study, we examined modulation of human neutrophil antimicrobial functions by F. alocis. Both non-opsonised and serum-opsonised F. alocis were engulfed by neutrophils but were not efficiently eliminated. Challenge of neutrophils with either non-opsonised or serum-opsonised F. alocis induced a minimal intracellular as well as extracellular respiratory burst response compared to opsonised Staphylococcus aureus and fMLF, respectively. However, pretreatment or simultaneous challenge of neutrophils with F. alocis did not affect the subsequent oxidative response to a particulate stimulus, suggesting that the inability to trigger the respiratory response was only localised to F. alocis phagosomes. In addition, although neutrophils engulfed live or heat-killed F. alocis with the same efficiency, heat-killed F. alocis elicited a higher intracellular respiratory burst response compared to viable organisms, along with decreased surface expression of CD35, a marker of secretory vesicles. F. alocis phagosomes remained immature by delayed and reduced recruitment of specific and azurophil granules, respectively. These results suggest that F. alocis withstands neutrophil antimicrobial responses by preventing intracellular ROS production, along with specific and azurophil granule recruitment to the bacterial phagosome.

Whole Transcriptome Analysis Reveals That Filifactor alocis Modulates TNFα-Stimulated MAPK Activation in Human Neutrophils

“…Together, this data shows that F. alocis challenge induces temporal changes in neutrophil functional mechanisms like cytokine production, chemotaxis, vesicular trafficking, and degranulation, as well as neutrophil biochemical mechanisms like the regulation of signaling pathways and metabolism. This coincides with previous data from our laboratory that shows that F. alocis affects neutrophil cytokine production, chemotaxis, vesicle trafficking, and degranulation functions (21,22).…”

“…However, oral pathogens have evolved mechanisms to manipulate neutrophil functional responses to prevent being killed while propagating inflammation (17,19). Previous work from our laboratory has shown that despite efficient phagocytosis by neutrophils, F. alocis survives within neutrophils by inducing minimal production of intracellular ROS and curtailing the fusion of antimicrobial granules with its phagosome (20,21). However, in comparison to the keystone oral pathogen, P. gingivalis, and another emerging oral pathogen, Peptoanaerobacter stomatis, challenge with F. alocis resulted in a mild release of neutrophil-derived proinflammatory cytokines, which resulted in limited recruitment of monocytes and other neutrophils (22).…”

Human Neutrophil Granule Exocytosis in Response to Mycobacterium smegmatis

“…To the best of our knowledge, the immediate pattern of exocytosis of human neutrophil granules is unique to M. smegmatis. While other bacteria have been shown to block or induce degranulation of some or all neutrophil granule subtypes [32,[49][50][51][52][53][54][55][56][57][58][59], release of only gelatinase granules at early time points has not been seen with bacteria other than M. smegmatis. An important distinction is that M. smegmatis is not preventing granule release to other stimuli, since granule mobilization was not affected upon fMLF stimulation by human neutrophils cultured with M. smegmatis.…”

Anti‐β2GPI/β2GPI induces human neutrophils to generate NETs by relying on ROS

“…1 As one of the first lines of defence, they are essential in the response to pathogen invasion. 3 Neutrophils receive an innovative pattern of apoptosis programing signals known as NETosis that induces the release of neutrophil extracellular traps (NETs), which are composed of double-stranded DNA resembling a net with a histone coating as well as antimicrobial agents including myeloperoxidase. 3 Neutrophils receive an innovative pattern of apoptosis programing signals known as NETosis that induces the release of neutrophil extracellular traps (NETs), which are composed of double-stranded DNA resembling a net with a histone coating as well as antimicrobial agents including myeloperoxidase.…”

“…2 They eradicate bacteria via phagocytosis or by releasing antimicrobial proteins in degranulation. 3 Neutrophils receive an innovative pattern of apoptosis programing signals known as NETosis that induces the release of neutrophil extracellular traps (NETs), which are composed of double-stranded DNA resembling a net with a histone coating as well as antimicrobial agents including myeloperoxidase. 4,5 NETs attract and eradicate bacteria and counteract viruses.…”