The Journal of immunology : official journal of the American Association of Immunologists
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MyD88 is a Toll/IL-1 receptor (TIR) domain-containing adapter common to signaling pathways via Toll-like receptor (TLR) family. However, accumulating evidence demonstrates the existence of a MyD88-independent pathway, which may explain unique biological responses of individual TLRs, particularly TLR3 and TLR4. TIR domain-containing adapter protein (TIRAP)/MyD88 adapter-like, a second adapter harboring the TIR domain, is essential for MyD88-dependent TLR2 and TLR4 signaling pathways, but not for MyD88-independent pathways. ⋯ Dominant-negative TRIF inhibited TLR3-dependent activation of both the NF-kappaB-dependent and IFN-beta promoters. TRIF associated with TLR3 and IFN regulatory factor 3. These findings suggest that TRIF is involved in the TLR signaling, particularly in the MyD88-independent pathway.
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Diffuse alveolar damage is the histopathological hallmark of acute respiratory distress syndrome (ARDS) and is a stereotypic response to a variety of etiologies. Moreover, a significant proportion of ARDS survivors have residual pulmonary fibrosis and compromised pulmonary function. This suggests that the pathogenesis of diffuse alveolar damage that ultimately leads to the chronic fibrosis of ARDS has features of dysregulated repair exemplified by exaggerated intra-alveolar angiogenesis and fibrogenesis (i.e., fibroproliferation and deposition of extracellular matrix), leading to progressive alveolar fibrosis and impaired lung function. ⋯ Furthermore, these levels correlated with both procollagen I and procollagen III levels in BALF. In contrast, while BALF levels of vascular endothelial growth factor were elevated, vascular endothelial growth factor did not appear to be significantly contributing to the angiogenic activity. These findings suggest that CXC chemokines have an important role in the fibroproliferative phase of ARDS via the regulation of angiogenesis.
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Caspase-1, the prototypic caspase, is known to process the cytokines IL-1beta and IL-18 to mature forms but it is unclear whether, like other caspases, it can induce apoptosis by activation of downstream protease cascades. Neutrophils are known to express caspase-1, to release IL-1beta and to undergo rapid, caspase-dependent apoptosis. We examined apoptosis and IL-1beta production in peripheral blood neutrophils of caspase-1-deficient and wild-type mice. ⋯ Caspase-1-deficient mice showed increased, predominantly neutrophilic pulmonary inflammation, but inflammation had resolved in both wild-type and deficient animals by 72 h after LPS instillation. IL-1beta production was increased in wild-type lungs but was also detected in caspase-1-deficient mice. We conclude that caspase-1 modulates apoptosis of both peripheral blood and inflammatory neutrophils, but is not essential for IL-1beta production in the lung.