Immunologic environment influences macrophage response to Porphyromonas gingivalis.

Macrophages adapt both phenotypically and functionally to the cytokine balance in host tissue microenvironments. Recent studies established that macrophages contribute an important yet poorly understood role in the development of infection-elicited oral bone loss. We hypothesized that macrophage adaptation to inflammatory signals encountered before pathogen interaction would significantly influence the subsequent immune response of these cells to the keystone oral pathobiont Porphyromonas gingivalis. Employing classically activated (M1) and alternatively activated (M2) murine bone-marrow-derived macrophage (BMDMø), we observed that immunologic activation of macrophages before P. gingivalis challenge dictated phenotype-specific changes in the expression of inflammation-associated molecules important to sensing and tuning host response to bacterial infection including Toll-like receptors 2 and 4, CD14, CD18 and CD11b (together comprising CR3), major histocompatibility complex class II, CD80, and CD86. M2 cells responded to P. gingivalis with higher expression of tumor necrosis factor-α, interleukin-6, monocyte chemoattractant protein-1, macrophage inflammatory protein-1α, regulated on activation normal T cell expressed and secreted, and KC than M1 cells. M1 BMDMø expressed higher levels of interleukin-10 to P. gingivalis than M2 BMDMø. Functionally, we observed that M2 BMDMø bound P. gingivalis more robustly than M1 BMDMø. These data describe an important contribution of macrophage skewing in the subsequent development of the cellular immune response to P. gingivalis.

Mast Cell Serotonin Immunoregulatory Effects Impacting on Neuronal Function: Implications for Neurodegenerative and Psychiatric Disorders.

Mast cells (MCs) are derived from hemopoietic precursor cells, undergo their maturation in peripheral tissues, and play a significant role in both the innate and adaptive immune response. Cross-linking of the FcεRI on MCs initiates activation of several cytoplasmic protein tyrosine kinases which rapidly lead to phosphorylation and recruitment of adaptor molecules. These effects trigger the release of preformed mediators stored in the cytoplasmic granules, including histamine, serotonin and tryptase, as well as newly synthesized mediators, such as cytokines/chemokines, prostaglandins, leukotrienes, and growth factors. Serotonin (5-HT) is a bioactive monoamine, which has seven specific cell surface membrane bound receptors which are coupled to G-proteins, plays an important role in the central and peripheral nervous system, and is one of the key mediators in signaling between nervous and immune systems. Serotonin is not stored in all MC types but is implicated in MC adhesion, chemotaxis, tumorigenesis, and tissue regeneration through smooth muscle differentiation of stromal cells. Recent evidence indicates that serotonin has immunoregulatory actions that may be important in neuropsychiatric conditions. Chemokines, RANTES/CCL5, MCP-1/CCL2, and related molecules, constitute the C-C class of chemokine supergene family, play a role in regulating T helper-cell cytokine production and MC trafficking, and are involved in histamine and serotonin generation and MC functions. Pro-inflammatory cytokines such as interleukin-1-ß and tumor necrosis factor which mediate MC response, are capable of activating p38 MAPK, and might increase serotonin generation through p38 MAPK activation. Here, we review the relationship between MCs and serotonin and its role in inflammatory diseases and neuroimmune interactions.

Liver X receptors contribute to periodontal pathogen-elicited inflammation and oral bone loss.

Periodontal diseases are chronic oral inflammatory diseases that are polymicrobial in nature. The presence of specific bacteria in subgingival plaque such as Porphyromonas gingivalis is associated with microbial dysbiosis and the modulation of host immune response. Bacterially elicited innate immune activation and inflammation are key elements implicated in the destruction of soft and hard tissues supporting the teeth. Liver X receptors (LXRs) are nuclear hormone receptors with important function in lipid homeostasis, inflammation, and host response to infection; however, their contribution to chronic inflammatory diseases such as periodontal disease is not understood. The aim of this study was to define the contribution of LXRs in the development of immune response to P. gingivalis and to assess the roles that LXRs play in infection-elicited oral bone loss. Employing macrophages, we observed that P. gingivalis challenge led to reduced LXRα and LXRß gene expression compared with that observed with unchallenged wild-type cells. Myeloid differentiation primary response gene 88 (MyD88)-independent, Toll/interleukin-1 receptor-domain-containing adapter-inducing interferon-ß (TRIF)-dependent signaling affected P. gingivalis-mediated reduction in LXRα expression, whereas neither pathway influenced the P. gingivalis effect on LXRß expression. Employing LXR agonist and mice deficient in LXRs, we observed functional effects of LXRs in the development of a P. gingivalis-elicited cytokine response at the level of the macrophage, and participation of LXRs in P. gingivalis-elicited oral bone loss. These findings identify novel importance for LXRs in the pathogenesis of P. gingivalis infection-elicited inflammation and oral bone loss.

Aging and contribution of MyD88 and TRIF to expression of TLR pathway-associated genes following stimulation with Porphyromonas gingivalis.

BACKGROUND AND OBJECTIVE: Periodontal disease is a highly complex chronic inflammatory disease of the oral cavity. Multiple factors influence periodontal disease, including socio-economic status, genetics and age; however, inflammation elicited by the presence of specific bacteria in the subgingival space is thought to drive the majority of soft- and hard-tissue destruction. Porphyromonas gingivalis is closely associated with periodontal disease. Toll-like receptors (TLRs) and their intracellular signaling pathways play roles in the host response to P. gingivalis. The focus of the current study was to use microarray analysis to define the contributions of the TLR adaptor molecules myeloid differentiation factor 88 (MyD88) and Toll/interleukin-1 receptor domain-containing adaptor inducing interferon-beta (TRIF), and aging, on the expression of TLR pathway-associated mRNAs in response to P. gingivalis. MATERIAL AND METHODS: Bone marrow-derived macrophages (BMØ) from wild-type (Wt), MyD88 knockout (MyD88-KO) and Trif(Lps2) [i.e. containing a point mutation in the lipopolysaccharide 2 (Lps2) gene rendering the Toll/interleukin (IL)-1 receptor domain-containing adaptor inducing interferon-beta (TRIF) protein nonfunctional] mice, at 2-and 12-mo of age, were cultured with P. gingivalis. Expression of genes in BMØ cultured with P. gingivalis was determined in comparison with expression of genes in BMØ cultured in medium only. RESULTS: Using, as criteria, a twofold increase or decrease in mRNA expression, differential expression of 32 genes was observed when Wt BMØ from 2-mo-old mice were cultured with P. gingivalis compared with the medium-only control. When compared with 2-mo-old Wt mice, 21 and 12 genes were differentially expressed (p < 0.05) as a result of the mutations in MyD88 or TRIF, respectively. The expression of five genes was significantly (p < 0.05) reduced in Wt BMØ from 12-mo-old mice compared with those from 2-mo-old mice following culture with P. gingivalis. Age also influenced the expression of genes in MyD88-KO and Trif(Lps2) mice challenged with P. gingivalis. CONCLUSIONS: Our results indicate that P. gingivalis induces differential expression of TLR pathway-associated genes, and both MyD88 and TRIF play roles in the expression of these genes. Age also played a role in the expression of TLR-associated genes following stimulation of BMØ with P. gingivalis.

Vascular endothelial growth factor (VEGF), mast cells and inflammation.

Vascular endothelial growth factor (VEGF) is one of the most important inducers of angiogenesis, therefore blocking angiogenesis has led to great promise in the treatment of various cancers and inflammatory diseases. VEGF, expressed in response to soluble mediators such as cytokines and growth factors, is important in the physiological development of blood vessels as well as development of vessels in tumors. In cancer patients VEGF levels are increased, and the expression of VEGF is associated with poor prognosis in diseases. VEGF is a mediator of angiogenesis and inflammation which are closely integrated processes in a number of physiological and pathological conditions including obesity, psoriasis, autoimmune diseases and tumor. Mast cells can be activated by anti-IgE to release potent mediators of inflammation and can also respond to bacterial or viral antigens, cytokines, growth factors and hormones, leading to differential release of distinct mediators without degranulation. Substance P strongly induces VEGF in mast cells, and IL-33 contributes to the stimulation and release of VEGF in human mast cells in a dose-dependent manner and acts synergistically in combination with Substance P. Here we report a strong link between VEGF and mast cells and we depict their role in inflammation and immunity.

Role of MyD88-dependent and MyD88-independent signaling in Porphyromonas gingivalis-elicited macrophage foam cell formation.

Clinical studies and experimental modeling identify a potential link between periodontal disease and periodontal pathogens such as Porphyromonas gingivalis and atherosclerosis and formation of macrophage foam cells. Toll-like receptors and molecules governing their intracellular signaling pathways such as MyD88 play roles in atherosclerosis, as well as host response to P. gingivalis. The aim of this study was to define roles of MyD88 and TRIF during macrophage foam cell formation in response to P. gingivalis. In the presence of human low-density lipoprotein (LDL) mouse bone-marrow-derived macrophages (BMφ) cultured with P. gingivalis responded with significant reduction in tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6). The BMφ stained strongly with oil red O, regardless of whether bacterial challenge occurred concurrent with or before LDL treatment. Heat-killed P. gingivalis stimulated foam cell formation in a similar way to live bacteria. The BMφ from MyD88-knockout and Lps2 mice revealed a significant role for MyD88, and a minor role for TRIF in P. gingivalis-elicited foam cell formation. Porphyromonas gingivalis-elicited TNF-α and IL-6 were affected by MyD88 ablation and to a lesser extent by TRIF status. These data indicate that LDL affects the TNF-α and IL-6 response of macrophages to P. gingivalis challenge and that MyD88 and TRIF play important roles in P. gingivalis-elicited foam cell formation.

Atherosclerosis: a classic inflammatory disease.

Atherosclerosis is an inflammatory disease due to a diet high in saturated fat, hypercholesterolemia, obesity, hypoglycemia, etc. mainly mediated by the infiltration of macrophage and T cells into the vascular wall. Once the endothelial is damaged monocytes penetrate the tissue and are transformed in scavenger cells. Upon stimulation of Th1 cells, a group of cytokines is released and contributes to the inflammatory response of atherosclerotic tissue. When macrophages proliferate they amplify inflammatory response through the secretion of growth factors and cytokines such as TNF and IL-1. In addition, chemokines such as RANTES and other C-C chemokines are generated, and matrix metalloprotinease 9 (MMP-9) are produced by activated monocytes. However, the immune system in atherosclerosis still remains unclear. Here, in this study we revisited the inter-relationship between atherosclerosis and inflammation.

VEGF, substance P and stress, new aspects: a revisited study.

Mast cells play an essential role in diverse physiological and pathological processes, such as atherosclerosis, malignancy, asthma, pulmonary fibrosis and arthritis, directly interact with bacteria, and appear to play a vital role in host defense against pathogens. Mast cells could be recruited in the inflammatory site, by MCP-1, RANTES and SCF, to selectively secrete proinflammatory molecules; these could include growth factors, histamine, which is mitogenic (H1) and an immunosuppressant (H2), neovascularization agents, such as heparin, IL-8, and VEGF, as well as proteases that could permit new blood vessel formation. Neurogenic inflammation involves vasodilation and plasma protein extravasation in response to neural stimulation. Upon stimulation, sensory neurons release Substance P and other neuropeptides and activate neurokinin-1 receptors leading to plasma protein extravasation from post-capillary venules. Substance P is a neuropeptide that is released from nerve endings in many tissues and plays an important role in immunological and inflammatory states, and it is also a mediator of tissue injury, asthma, arthritis, allergy and autoimmune diseases. SP-positive nerve fibers and mast cell contacts are increased by acute stress in mice leading to dermal mast cell degranulation. VEGF is produced by flammatory cells. IL-33 is the newest inflammatory member of the IL-1 cytokine family and we show here that SP can induce VEGF secretion from mast cells and IL-33 augments the effect of SP in VEGF transcription and translation protein.