Th1 cells directly respond to short-chain LPS. Cigarette smoking suppresses Th1-mediated immune responses to gram-negative bacterial infections by interfering with MyD88/IRAK signaling thereby reducing LPS-induced TLR4 expression. This can explain the increased susceptibility to bacterial infections in COPD. Targeting TLR signaling might be useful to reduce exacerbation rates.

BackgroundThe endocannabinoid 2-arachidonoylglycerol (2-AG) is a known modulator of inflammation. Despite its high concentration in vascular tissue, the role of 2-AG in atherogenesis has not yet been examined.MethodsApoE-deficient mice were sublethally irradiated and reconstituted with bone marrow from mice with a myeloid-specific knockout of the 2-AG synthesising enzyme diacylglycerol lipase α (Dagla) or control bone marrow with an intact 2-AG biosynthesis. After a cholesterol-rich diet for 8 weeks, plaque size and plaque morphology were examined in chimeric mice. Circulating inflammatory cells were assessed by flow cytometry. Aortic tissue and plasma levels of endocannabinoids were measured using liquid chromatography-multiple reaction monitoring.ResultsMice with Dagla-deficient bone marrow and circulating myeloid cells showed a significantly reduced plaque burden compared to controls. The reduction in plaque size was accompanied by a significantly diminished accumulation of both neutrophil granulocytes and macrophages in atherosclerotic lesions of Dagla-deficient mice. Moreover, CB2 expression and the amount of oxidised LDL within atherosclerotic lesions was significantly reduced. FACS analyses revealed that levels of circulating inflammatory cells were unaltered in Dagla-deficient mice.ConclusionsMyeloid synthesis of the endocannabinoid 2-AG appears to promote vascular inflammation and atherogenesis. Thus, myeloid-specific disruption of 2-AG synthesis may represent a potential novel therapeutic strategy against atherosclerosis.

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The rate of COPD exacerbations caused by bacteria correlates with a progress in disease severity. A complex of CD14 and TLR4 detects bacteria by recognition of LPS and induces protective immune responses. To elucidate the molecular basis for exacerbations, we studied TLR4 expression and cytokine release induced by LPS in monocytes and TH1−lymphocytes of non−smokers (N), smokers (S) and COPD patients (all n=10) via RT−PCR, Western blot, and ELISA. To functionally link TLR4 to cytokine dysregulation in COPD we performed transfection/overexpression experiments in primary monocytes with a construct encoding wildtype TLR4. In contrast to CD14, expression of TLR4 was induced by LPS (p<0.01) in monocytes and TH1 cells. In both cell types, this effect was increased in N compared to S and COPD (p<0.05; p<0.01) and was reduced by inhibition of ERK−1/−2 or p38MAPK (both p<0.01). LPS induced TNFα and GM−CSF release from monocytes and IFNγ release from TH1 cells to a lesser extent in S (not TNFα) and COPD compared to N (all p<0.05). Reduction of TNFα−, GM−CSF−, and IFNγ expression in response to LPS was correlated with pack years and decreasing FEV1 (all p<0.05). Transfection of COPD monocytes with a wildtype TLR4 (but not with a CD14) expression construct restored TNFα− and GM−CSF release in response to LPS. LPS induces the expression of TLR4 via ERK−1/−2 and p38MAPK pathways in monocytes and TH1 cells. LPS−induced TLR4 expression and cytokine release is disturbed in both cell types in S and COPD. Since TLR4 overexpression restores TNFα and GM−CSF release TLR4−downregulation explains the reduced cytokine release of COPD monocytes in response to LPS. Thus, TLR4 downregulation in monocytes and TH1 cells might explain the increased rate of exacerbations in COPD and TLR signaling agonists might be useful in therapy to reduce the rate of COPD exacerbations. This abstract is funded by: None.

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