Role Of Bacterial DNA Research Articles

The role of bacterial DNA containing CpG motifs in diseases.

Bacterial DNA containing unmethylated CpG motifs can activate immune cells to release proinflammatory cytokines. Here, the role of bacterial DNA containing CpG motifs in diseases with a focus on arthritis is discussed. Our studies demonstrate that the intraarticular injection of bacterial DNA and oligodeoxynucleotides containing CpG motifs (CpG ODN) induced arthritis. The induction of arthritis involves the role of macrophages over other cells such as neutrophils, NK cells, and lymphocytes. TNF-α and TNFRI play an important role in the development of arthritis. NF-κB also plays a critical regulatory role in arthritis. Systemic anti-inflammatory treatment, along with antibiotic therapy, has beneficial effects on the course and the outcome of bacterial arthritis. Thus, future treatment strategies for bacterial arthritis should include attempts to minimizing bacterial growth while blocking the proinflammatory effects of the bacterial DNA. Significant therapeutic efficiency has also been shown by CpG ODN-mediated Th1 immune activation in mouse models of cancer, infectious disease, and allergy/asthma.

The Diagnostic Role of Bacterial DNA in Ascitic Fluid Infection in Patients with Cirrhotic Ascites

Background: Patients with cirrhosis and ascites carry a high risk of ascitic fluid (AF) infection. Identification of bacterial DNA in patients with cirrhotic ascites may provide a rapid and accurate tool helping in diagnosis of AF infection when it is compared with culture-based methodology to initiate treatment in such cases. Objectives: This study was aimed to evaluate the efficacy of broad range 16 S ribosomal RNA gene polymerase chain reaction (PCR) in diagnosis of AF infection. Methdology: A total of 130 liver cirrhotic ascetic patients were subjected to thorough history, clinical examination, laboratory investigations including, AF samples analysis for polymorh nuclear leucocytic (PMN) count, bacterial culture and PCR- bacterial DNA detection. Results: The sensitivities of PMN count, culture and PCR in diagnosing AF infection were 73.8%, 31.5% and 80.1% respectively, while the accuracies were 77.6%, 41.5% and 83% respectively. Conclusion: Bacterial DNA in AF samples might be an alternative diagnostic method to AF bacterial culture and PMN count in early diagnosis and promp treatment of AF infection.

TLR9 signaling regulates tissue factor and tissue factor pathway inhibitor expression and activity in human coronary artery endothelial cells

Although human endothelial cells recognize and respond to bacterial DNA (CpG DNA), the role of bacterial DNA in procoagulation is not known. We investigated the impact of bacterial DNA on expression and activity of tissue factor (TF) and tissue factor pathway inhibitor (TFPI) in human coronary artery endothelial cells (HCAEC). CpG DNA (1–32 μg/ml) markedly induced TF expression between 4 and 8 hours in both protein and mRNA levels and TF activity. CpG DNA markedly enhanced NF‐êB activation, which was blocked by the telomere‐derived TLR9 antagonist oligonucleotide TTAGGG. Consistently, the specific NF‐êB inhibitors BAY 117082 and SN50 prevented CpG DNA‐induced TF transcription and secretion. Conversely, culture of HCAEC with CpG DNA for 24 to 48 hours reduced TFPI transcription, secretion, and activity. Methylation of cytosines in CpG DNA resulted in a complete loss of biological activities. Our results demonstrate that bacterial DNA through TLR9 can alter the balance of TF and TFPI expression and activity in HCAEC, thereby contributing to thrombus formation, the major cause of acute coronary artery disease.(Grant support: CIHR MOP‐97742).

Monocyte-Mediated Inhibition of TLR9-Dependent IFN-α Induction in Plasmacytoid Dendritic Cells Questions Bacterial DNA as the Active Ingredient of Bacterial Lysates

Bacterial DNA contains unmethylated CpG dinucleotides and is a potent ligand for TLR9. Bacterial DNA has been claimed the active ingredient in bacterial lysates used for immunotherapy. Whereas the detection of viral DNA by TLR9 expressed in plasmacytoid dendritic cells (PDCs) with subsequent IFN-α production is well defined, the role of bacterial DNA during microbial infection is less clear. In fact, IFN-α is not a hallmark of antibacterial immune responses. Unlike in mice, TLR9 expression in humans is restricted to PDCs and B cells; thus, conclusions from murine models of infection have limitations. In this study, we demonstrate that lysates of heat-killed Escherichia coli containing bacterial DNA induced IFN-α in isolated PDCs but not in the mixed cell populations of human PBMCs. Depletion of monocytes restored IFN-α secretion by PDCs within PBMCs. We found that monocyte-derived IL-10 and PGs contribute to monocyte-mediated inhibition of IFN-α release in PDCs. We conclude that human PDCs can be stimulated by bacterial DNA via TLR9; however, in the physiological context of mixed-cell populations, PDC activation is blocked by factors released from monocytes stimulated in parallel by other components of bacterial lysates such as LPS. This functional repression of PDCs by concomitantly stimulated monocytes avoids production of antiviral IFN-α during bacterial infection and thus explains how the innate immune system is enabled to distinguish bacterial from viral CpG DNA and thus to elicit the appropriate responses despite the presence of CpG DNA in both types of infection.

Inflammatory Bowel Diseases: When Natural Friends Turn into Enemies—The Importance of CpG Motifs of Bacterial DNA in Intestinal Homeostasis and Chronic Intestinal Inflammation

From numerous studies during the last years it became evident that bacteria and bacterial constituents play a decisive role both in the maintenance of intestinal immune homeostasis as well as in the development and perpetuation of chronic intestinal inflammation. In this review we focus on the role of bacterial DNA which is a potent immunomodulatory component of the bacterial flora. Bacterial DNA has been shown to be protective against experimental colitis. In contrast bacterial DNA essentially contributes to the perpetuation of an already established chronic intestinal inflammation in a Toll-like receptor (TLR)9-dependent manner. This dichotomic action may be explained by a different activation status of essential regulators of TLR signaling like Glycogen synthase kinase 3-β (GSK3-β) depending on the pre-activation status of the intestinal immune system. In this review we suggest that regulators of TLR signaling may be interesting therapeutic targets in IBD aiming at the restoration of intestinal immune homeostasis.

Role of bacterial DNA in macrophage activation by group B streptococci

Bacterial DNA (CpG DNA) induces macrophage activation and the production of inflammatory mediators, including tumor necrosis factor (TNF) and nitric oxide (NO) by these cells. However, the role of bacterial DNA in the macrophage response to whole bacteria is unknown. We used overlapping strategies to estimate the relative contribution of bacterial DNA to the upregulation of TNF and NO production in macrophages stimulated with antibiotic-treated group B streptococci (GBS). Selective inhibitors of the bacterial DNA/TLR9 pathway (chloroquine, an inhibitory oligonucleotide, and DNase I) consistently inhibited GBS-induced TNF secretion by 35–50% in RAW 264.7 macrophages and murine splenic macrophages, but had no effect on inducible nitric oxide synthase (iNOS) accumulation or NO secretion. Similarly, splenic and peritoneal macrophages from mice lacking TLR9 expression secreted 40% less TNF than macrophages from control mice after GBS challenge but accumulated comparable amounts of iNOS protein. Finally, studies in both RAW 264.7 cells and macrophages from TLR9−/− mice implicated GBS DNA in the upregulation of interleukins 6 (IL-6) and 12 (IL-12) but not interferon-beta (IFNβ), a key intermediary in macrophage production of iNOS/NO. Our data suggest that the bacterial DNA/TLR9 pathway plays an important role in stimulating TNF rather than NO production in macrophages exposed to antibiotic-treated GBS, and that TLR9-independent upregulation of IFNβ production by whole GBS may account for this difference.

The Role of Bacterial DNA in Inflammatory and Allergic Disease

Bacterial infections can be localized to joints and brain causing septic arthritis and meningitis. Despite early and adequate antibiotic treatment, bacterial meningitis and arthritis remain an infection with a high mortality rate and severe sequelae. Bacterial DNA has recently been shown to exert immunostimulatory effects on leukocytes. We speculate that bacterial DNA may be involved in the process of bacterial arthritis and meningitis. We found that bacterial DNA and oligonucleotides containing unmethylated CpG motifs induce arthritis and meningitis by intraarticular or intracisternal inoculation. Arthritis and meningitis induced by bacterial DNA were characterized by an influx of monocytic, Mac-1+ cells and by a lack of T cells. Macrophages and their products such as tumor necrosis factor (TNF) alpha are essential for development of arthritis and meningitis triggered by bacterial DNA containing CpG motifs. In contrast, neutrophils, NK cells, and T/B cells were not important in arthritis and meningitis triggered by bacterial DNA. CpG ODN is also found to reverse Th-2 dominant allergic diseases. This review discusses that the role and mechanism of bacterial DNA in inflammatory diseases and allergic disease. In this review patented strategies are also discussed.

A critical role of CpG motifs in a murine peritonitis model by their binding to highly expressed toll-like receptor-9 on liver NKT cells

Toll-like receptor (TLR)-9 plays a critical role in the recognition of the CpG motifs, which is frequently observed in bacterial DNA. To date, there have not been any reports regarding the role of bacterial DNA in the systemic circulation on the development of sepsis. We examined the expression of TLR-9 in the liver and spleen in a murine peritonitis model (CLP mice). We also measured the cytokine response of mononuclear cells (MNCs) from normal and CLP mice to CpG oligodeoxynucleotides (ODN) in vitro and in vivo. TLR-9 expression on F4/80(+) and NK1.1(+)CD3epsilon(+) cells in the liver of CLP mice was elevated compared to sham-operated mice. With regard to cytokine production, we found that CpG ODN markedly stimulated the production of inflammatory cytokines by murine macrophages and liver MNCs. The intravenous injection of CpG ODN in mice that underwent CLP 12h earlier led to their increased cytokine production and their increased mortality. In addition, the depletion of NK/NKT cells contributed to improve their survival rate. Our results suggest that, in patients with overwhelming bacterial infection, bacterial DNA may induce liver toxicity that is mediated by liver NKT cells and macrophages that express high levels of TLR-9.

Immunostimulatory DNA sequences influence the course of adjuvant arthritis.

Bacterial DNA is enriched in unmethylated CpG motifs that have been shown to activate the innate immune system. These immunostimulatory DNA sequences (ISS) induce inflammation when injected directly into joints. However, the role of bacterial DNA in systemic arthritis is not known. The purpose of the present experiments was to determine whether ISS contributes to the development of adjuvant arthritis in Lewis rats after intradermal injection of heat-killed Mycobacterium tuberculosis (Mtb). The results showed that Mtb DNA was necessary for maximal joint inflammation in adjuvant arthritis but could be replaced by synthetic ISS oligodeoxynucleotides. The arthritis-promoting effect of the Mtb DNA or of the ISS oligodeoxynucleotides correlated with an increased Th1 response to Mtb Ags, as measured by the production of IFN-gamma and increased production of the osteoclast differentiation factor, receptor activator of NF-kappaB ligand (RANKL). The Mtb DNA did not enter the joints but dispersed to the bone marrow and spleen before the onset of systemic joint inflammation. Thus, adjuvant arthritis is a microbial DNA-dependent disease. In this model, we postulate that massive and prolonged activation of macrophages, dendritic cells, and osteoclast precursors in the bone marrow may prime the joints for the induction of inflammatory Th1 immune responses to Mtb Ags.

Role of Bacterial Dna in Macrophage Activation by Group B Streptococci

Role of Bacterial Dna in Macrophage Activation by Group B Streptococci

The role of bacterial DNA in septic arthritis.

Unmethylated CpG motifs are frequently found in bacterial DNA and have recently been shown to exert immunostimulatory effects on leukocytes. Bacteria produce severe septic arthritis; bacterial DNA may be involved in this process. We injected intraarticularly bacterial DNA and oligonucleotides containing unmethylated CpG motifs into knee joints of mice. Arthritis was seen by histopathology within 2 h and lasted for at least 14 days, and was characterized by an influx of monocytic, Mac-1+ cells and by a lack of T lymphocytes. Macrophages and their products such as tumor necrosis factor (TNF) alpha are essential for development of arthritis triggered by bacterial DNA containing CpG motifs. In contrast, neurophils, NK cells, and T/B cells were not instrumental in this condition. This review demonstrates that bacterial DNA containing unmethylated CpG motifs induces arthritis and indicates an important pathogenic role for bacterial DNA in septic arthritis.

The role of bacterial DNA in autoantibody induction.

Bacterial DNA has potent immunological properties that can stimulate the immune system in SLE in both specific and non-specific ways. As such, this molecule may play an important role in disease pathogenesis, because it can exert immunomodulatory activity and function as a molecular mimic. Future studies will hopefully both determine the role of foreign nucleic acids in the induction of autoantibodies and lead to strategies for their elimination.