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Unresponsiveness of MyD88-deficient mice to endotoxin
1Department of Biochemistry, Hyogo College of Medicine, Nishinomiya, Japan.
Abstract:
MyD88 is a general adaptor protein that plays an important role in the Toll/IL-1 receptor family signalings. Recently, Toll-like receptors 2 and 4 (TLR2 and TLR4) have been suggested to be the signaling receptors for lipopolysaccharide (LPS). In this study, we demonstrate that MyD88 knockout mice lack the ability to respond to LPS as measured by shock response, B cell proliferative response, and secretion of cytokines by macrophages and embryonic fibroblasts. However, activation of neither NF-kappaB nor the mitogen-activated protein (MAP) kinase family is abolished in MyD88 knockout mice. These findings demonstrate that signaling via MyD88 is essential for LPS response, but the inability of MyD88 knockout mice to induce LPS-dependent gene expression cannot simply be attributed to lack of the activation of MAP kinases and NF-kappaB.
Insights
MyD88 adaptor protein is essential for lipopolysaccharide (LPS) response in mice, mediating shock and immune cell activation. However, LPS-induced gene expression is not solely dependent on NF-kappaB or MAP kinase activation.
Area of Science:
- Immunology
- Molecular Biology
Background:
- Myeloid differentiation primary response 88 (MyD88) is a key adaptor protein in Toll/IL-1 receptor signaling pathways.
- Toll-like receptors 2 and 4 (TLR2 and TLR4) are implicated as lipopolysaccharide (LPS) signaling receptors.
Purpose of the Study:
- To investigate the role of MyD88 in LPS-mediated signaling and immune responses.
- To determine if NF-kappaB and MAP kinase activation are solely responsible for LPS-induced gene expression.
Main Methods:
- Utilized MyD88 knockout mice to assess LPS response.
- Measured shock response, B cell proliferation, and cytokine secretion.
- Analyzed NF-kappaB and MAP kinase activation pathways.
Main Results:
- MyD88 knockout mice exhibited a complete lack of response to LPS.
- Impaired shock response, B cell proliferation, and cytokine secretion were observed.
- NF-kappaB and MAP kinase activation remained intact in MyD88 knockout mice.
Conclusions:
- MyD88-dependent signaling is critical for LPS response.
- The absence of LPS-induced gene expression in MyD88 knockout mice is not solely due to impaired NF-kappaB or MAP kinase activation.