Lipoteichoic acid of Enterococcus faecalis interferes with Porphyromonas gingivalis lipopolysaccharide signaling via IRAK-M upregulation in human periodontal ligament cells

Lipoproteins are key immunostimulatory components of Bacillus species for dendritic cell maturation and activation

Dendritic cells (DCs) play an important role in immunity by sensing and responding to invasive microbes. Bacillus species are rod-shaped sporulating bacteria that include the pathogenic Bacillus cereus and commensal Bacillus subtilis. Although the interaction between DC and these two Bacillus species has been studied, their key structural component that prompts DC activation is poorly understood. Here, we investigated the two Bacillus species in DC activation by whole cells and their representative microbe-associated molecular patterns (MAMPs). MAMPs including lipoteichoic acid (LTA), lipoprotein (LPP), and peptidoglycan (PGN) were purified from the two Bacillus species. Among the MAMPs, LPP from both species most potently induced the maturation and activation of DCs while PGN, but not LTA, moderately stimulated DCs. LPPs from both Bacillus species enhanced the expression of DC maturation markers including CCR7, CD40, CD80, CD83, CD86, CD205, MHC-I, and MHC-II. Among the MAMPs from B. cereus, PGN most considerably lowered the endocytic capacity of DCs implying DC maturation whereas PGN from B. subtilis lowered it to a similar degree to its LPP. Furthermore, DCs sensitized with LPPs from both Bacillus species and PGN from B. subtilis moderately induced TNF-α and IL-6 production. Notably, a combination of MAMPs did not show any synergistic effect on DC activation. Taken together, our results demonstrate that LPP is the key structural component in B. cereus and B. subtilis that leads to DC activation.

Lipoteichoic acid of Streptococcus gordonii as a negative regulator of human dendritic cell activation

Streptococcus gordonii, an opportunistic Gram-positive bacterium, causes an infective endocarditis that could be fatal to human health. Dendritic cells (DCs) are known to be involved in disease progression and immune responses in S. gordonii infection. Since lipoteichoic acid (LTA) is a representative virulence factor of S. gordonii, we here investigated its role in the activation of human DCs stimulated with LTA-deficient (ΔltaS) S. gordonii or S. gordonii LTA. DCs were differentiated from human blood-derived monocytes in the presence of GM-CSF and IL-4 for 6 days. DCs treated with heat-killed ΔltaS S. gordonii (ΔltaS HKSG) showed relatively higher binding and phagocytic activities than those treated with heat-killed wild-type S. gordonii (wild-type HKSG). Furthermore, ΔltaS HKSG was superior to wild-type HKSG in inducing phenotypic maturation markers including CD80, CD83, CD86, PD-L1, and PD-L2, antigen-presenting molecule MHC class II, and proinflammatory cytokines such as TNF-α and IL-6. Concomitantly, DCs treated with the ΔltaS HKSG induced better T cell activities, including proliferation and activation marker (CD25) expression, than those treated with the wild-type. LTA, but not lipoproteins, isolated from S. gordonii weakly activated TLR2 and barely affected the expression of phenotypic maturation markers or cytokines in DCs. Collectively, these results demonstrated that LTA is not a major immuno-stimulating agent of S. gordonii but rather it interferes with bacteria-induced DC maturation, suggesting its potential role in immune evasion.

Biological Roles of Fibroblasts in Periodontal Diseases

Periodontal diseases include periodontitis and gingival overgrowth. Periodontitis is a bacterial infectious disease, and its pathological cascade is regulated by many inflammatory cytokines secreted by immune or tissue cells, such as interleukin-6. In contrast, gingival overgrowth develops as a side effect of specific drugs, such as immunosuppressants, anticonvulsants, and calcium channel blockers. Human gingival fibroblasts (HGFs) are the most abundant cells in gingival connective tissue, and human periodontal ligament fibroblasts (HPLFs) are located between the teeth and alveolar bone. HGFs and HPLFs are both crucial for the remodeling and homeostasis of periodontal tissue, and their roles in the pathogenesis of periodontal diseases have been examined for 25 years. Various responses by HGFs or HPLFs contribute to the progression of periodontal diseases. This review summarizes the biological effects of HGFs and HPLFs on the pathogenesis of periodontal diseases.

Analysis of interleukin-1 receptor associated kinase-3 (IRAK3) function in modulating expression of inflammatory markers in cell culture models: A systematic review and meta-analysis

BACKGROUND

IRAK3 is a critical modulator of inflammation in innate immunity. IRAK3 is associated with many inflammatory diseases, including sepsis, and is required in endotoxin tolerance to maintain homeostasis of inflammation. The impact of IRAK3 on inflammatory markers such as nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), tumour necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in cell culture models remains controversial.

OBJECTIVE

To analyse temporal effects of IRAK3 on inflammatory markers after one- or two-challenge interventions in cell culture models.

METHODS

A systematic search was performed to identify in vitro cell studies reporting outcome measures of expression of IRAK3 and inflammatory markers. Meta-analyses were performed where sufficient data were available. Comparisons of outcome measures were performed between different cell lines and human and mouse primary cells.

RESULTS

The literature search identified 7766 studies for screening. After screening titles, abstracts and full-texts, a total of 89 studies were included in the systematic review.

CONCLUSIONS

The review identifies significant effects of IRAK3 on decreasing NF-κB DNA binding activity in cell lines, TNF-α protein level at intermediate time intervals (4h-15h) in cell lines or at long term intervals (16h-48h) in mouse primary cells following one-challenge. The patterns of TNF-α protein expression in human cell lines and human primary cells in response to one-challenge are more similar than in mouse primary cells. Meta-analyses confirm a negative correlation between IRAK3 and inflammatory cytokine (IL-6 and TNF-α) expression after two-challenges.

Bacterial Lipoproteins Induce BAFF Production via TLR2/MyD88/JNK Signaling Pathways in Dendritic Cells

B-cell activating factor (BAFF) plays a crucial role in survival, differentiation, and antibody secretion of B cells. Microbial products with B-cell mitogenic properties can indirectly promote expansion and activation of B cells by stimulating accessory cells, such as dendritic cells (DCs), to induce BAFF. Although bacterial lipoproteins are potent B-cell mitogen like lipopolysaccharides (LPSs), it is uncertain whether they can stimulate DCs to induce BAFF expression. Here, we evaluated the effect of bacterial lipoproteins on BAFF expression in mouse bone marrow-derived DCs. Lipoprotein-deficient Staphylococcus aureus mutant induced relatively low expression level of membrane-bound BAFF (mBAFF) and the mRNA compared with its wild-type strain, implying that bacterial lipoproteins can positively regulate BAFF induction. The synthetic lipopeptides Pam2CSK4 and Pam3CSK4, which mimic bacterial lipoproteins, dose-dependently induced BAFF expression, and their BAFF-inducing capacities were comparable to those of LPS in DCs. Induction of BAFF by the lipopeptide was higher than the induction by other microbe-associated molecular patterns, including peptidoglycan, flagellin, zymosan, lipoteichoic acid, and poly(I:C). Pam3CSK4 induced both mBAFF and soluble BAFF expression in a dose- and time-dependent manner. BAFF expression by Pam3CSK4 was completely absent in DCs from TLR2- or MyD88-deficient mice. Among various MAP kinase inhibitors, only JNK inhibitors blocked Pam3CSK4-induced BAFF mRNA expression, while inhibitors blocking ERK or p38 kinase had no such effect. Furthermore, Pam3CSK4 increased the DNA-binding activities of NF-κB and Sp1, but not that of C/EBP. Pam3CSK4-induced BAFF promoter activity via TLR2/1 was blocked by NF-κB or Sp1 inhibitor. Collectively, these results suggest that bacterial lipoproteins induce expression of BAFF through TLR2/MyD88/JNK signaling pathways leading to NF-κB and Sp1 activation in DCs, and BAFF derived from bacterial lipoprotein-stimulated DCs induces B-cell proliferation.