Production and role of IL-17 and related cytokines in response to respiratory pathogens

Background: Pneumonia is a disease of the lungs that is caused by a number of pathogens including Gram-negative Pseudomonas aeruginosa and Gram-positive Streptococcus pneumoniae. These pathogens are prevalent causes of hospital-acquired pneumonia, and P. aeruginosa is particularly problematic with regards to chronic pulmonary infection in patients with Cystic Fibrosis (CF). Antibodies are known to provide a component of host-defence against this microbe, but recent evidence suggests that cells secreting the pro-inflammatory cytokine interleukin-17 (IL-17), namely T helper 17 (Th17) cells, are also significant in these responses. Aim: To investigate the sources of IL-17 and related cytokines during P. aeruginosa and S. pneumoniae infection, and to investigate if IL-1β has a role in Th17 formation during infection with these pathogens. Furthermore, to investigate the cytokine secretion of dendritic cells (DCs) derived from different sources following infection with these pathogens, and their roles at inducing Th17 secretion from naive CD4+ T cells. Methods & Results: Dendritic cells from mucosal sites were found to be better than GM-CSF derived bone marrow dendritic cells (BMDCs) at inducing Th17 cells from naive T cells. Th17 cells were derived in response to both P. aeruginosa and S. pneumoniae, with the role of IL-1β seeming to be negligible for P. aeruginosa. However, the role of IL-1β during Th17 cell induction during S. pneumoniae is unclear and needs further investigation. γδ T cells were found to be a source of IL-17 during P. aeruginosa infection in a IL-23 dependent manner. Furthermore, γδ T cells were also found to be a source of IL-22, yet the majority of cells were either IL-17 or IL-22 producing, not double producers as expected. In vivo infection with these pathogens identifed γδ T cells to be a main source of IL-17 during P. aeruginosa infection, with Th17 cells having more of a role during S. pneumoniae infection, yet the main sources of IL-17 still need to be identified. Preliminary infections with S. pneumoniae in IL-17RKO mice identified IL-17 as a key mediator in downstream inflammatory responses in the lung during infection. Conclusions: This study demonstrates that IL-17 responses are induced in response to infection with the respiratory pathogens P. aeruginosa and S. pneumoniae. Ex vivo, mucosal DCs were found to induce more robust Th17 cell responses compared to GM-CSF derived BMDCS. In vivo, Th17 cells appear to have a role in S. pneumoniae infection, with γδ T cells appearing to be the dominant source of IL-17 during P. aeruginosa infection. Furthermore, in vitro investigations of γδ T cells found them to be differentially IL-17 and IL-22 producing in response to P. aeruginosa infection, in a DC contact independent manner

The alpha 7 nicotinic receptor agonist PHA-543613 hydrochloride inhibits <i>Porphyromonas gingivalis</i>-induced expression of interleukin-8 by oral keratinocytes

Objective: The alpha 7 nicotinic receptor (α7nAChR) is expressed by oral keratinocytes. α7nAChR activation mediates anti-inflammatory responses. The objective of this study was to determine if α7nAChR activation inhibited pathogen-induced interleukin-8 (IL-8) expression by oral keratinocytes.&lt;p&gt;&lt;/p&gt; Materials and methods: Periodontal tissue expression of α7nAChR was determined by real-time PCR. OKF6/TERT-2 oral keratinocytes were exposed to &lt;i&gt;Porphyromonas gingivalis&lt;/i&gt; in the presence and absence of a α7nAChR agonist (PHA-543613 hydrochloride) alone or after pre-exposure to a specific α7nAChR antagonist (α-bungarotoxin). Interleukin-8 (IL-8) expression was measured by ELISA and real-time PCR. Phosphorylation of the NF-κB p65 subunit was determined using an NF-κB p65 profiler assay and STAT-3 activation by STAT-3 in-cell ELISA. The release of ACh from oral keratinocytes in response to &lt;i&gt;P. gingivalis&lt;/i&gt; lipopolysaccharide was determined using a GeneBLAzer M3 CHO-K1-blacell reporter assay.&lt;p&gt;&lt;/p&gt; Results: Expression of α7nAChR mRNA was elevated in diseased periodontal tissue. PHA-543613 hydrochloride inhibited &lt;i&gt;P. Gingivalis&lt;/i&gt;-induced expression of IL-8 at the transcriptional level. This effect was abolished when cells were pre-exposed to a specific α7nAChR antagonist, α-bungarotoxin. PHA-543613 hydrochloride downregulated NF-κB signalling through reduced phosphorylation of the NF-κB p65-subunit. In addition, PHA-543613 hydrochloride promoted STAT-3 signalling by maintenance of phosphorylation. Furthermore, oral keratinocytes upregulated ACh release in response to &lt;i&gt;P. Gingivalis&lt;/i&gt; lipopolysaccharide.&lt;p&gt;&lt;/p&gt; Conclusion: These data suggest that α7nAChR plays a role in regulating the innate immune responses of oral keratinocytes.&lt;p&gt;&lt;/p&gt

Clinical associations between IL-17 family cytokines and periodontitis and potential differential roles for IL-17A and IL-17E in periodontal immunity

&lt;b&gt;Objective&lt;/b&gt; IL-17A is implicated in periodontitis pathogenesis. The roles of IL-17B–IL-17F and IL-17A/F are unknown. This study aimed to determine clinical associations between IL-17 family cytokines and periodontitis and to investigate the biological roles of IL-17A and IL-17E using in vitro model systems.&lt;p&gt;&lt;/p&gt; &lt;b&gt;Materials and methods&lt;/b&gt; Samples from 97 patients with periodontitis and 77 healthy volunteers were used in the study. Serum, saliva and gingival crevicular fluid (GCF) levels of IL-17 family cytokines were measured by ELISA. Oral keratinocytes were stimulated with a P. gingivalis biofilm, or IL-17A, in the presence and absence of IL-17E and the expression of IL-8 and CXCL5 were investigated by ELISA and real-time-PCR. NF-κB phosphorylation in similar experiments was also measured using a cell-based ELISA.&lt;p&gt;&lt;/p&gt; &lt;b&gt;Results&lt;/b&gt; Serum, saliva and GCF IL-17A levels were higher in periodontitis patients and correlated positively with clinical parameters of attachment loss, pocket depth and bleeding on probing. Serum IL-17E levels were lower in periodontitis patients and the serum IL-17A:IL-17E ratio correlated positively with clinical parameters. In vitro, IL-17E inhibited Porphyromonas gingivalis and IL-17A induced expression of chemokines by reducing phosphorylation of the NF-κB p65 subunit.&lt;p&gt;&lt;/p&gt; &lt;b&gt;Conclusions&lt;/b&gt; Serum IL-17A:IL-17E may be a marker of disease severity. IL-17E may have opposing roles to IL-17A in periodontitis pathogenesis. IL-17E can negatively regulate IL-17A and periodontal pathogen induced expression of chemokines by oral keratinocytes.&lt;p&gt;&lt;/p&gt