Recently, a large number of experimenters have found that the pathogenesis of Parkinson’s disease may be related to the gut microbiome and proposed the microbiome–gut–brain axis. Studies have shown that Toll-like receptors, especially Toll-like receptor 2 (TLR2) and Toll-like receptor 4 (TLR4), are key mediators of gut homeostasis. In addition to their established role in innate immunity throughout the body, research is increasingly showing that the Toll-like receptor 2 and Toll-like receptor 4 signaling pathways shape the development and function of the gut and enteric nervous system. Notably, Toll-like receptor 2 and Toll-like receptor 4 are dysregulated in Parkinson’s disease patients and may therefore be identified as the core of early gut dysfunction in Parkinson’s disease. To better understand the contribution of Toll-like receptor 2 and Toll-like receptor 4 dysfunction in the gut to early α-synuclein aggregation, we discussed the structural function of Toll-like receptor 2 and Toll-like receptor 4 and signal transduction of Toll-like receptor 2 and Toll-like receptor 4 in Parkinson’s disease by reviewing clinical, animal models, and in vitro studies. We also present a conceptual model of the pathogenesis of Parkinson’s disease, in which microbial dysbiosis alters the gut barrier as well as the Toll-like receptor 2 and Toll-like receptor 4 signaling pathways, ultimately leading to a positive feedback loop for chronic gut dysfunction, promoting α-synuclein aggregation in the gut and vagus nerve.

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This article proposes an ultra‐compact orthomode transducer (OMT) with novel taper branching structure. By combing the taper section and split part, the overall OMT can be implemented in a monoblock, which is as small as waveguide flanges. Furthermore, the good matching effect achieved by ridge and split makes the OMT maintaining the most compact structure with high performance. The whole structure can be fabricated using the conventional computer numerical control milling technique. A K‐band OMT is designed and tested. The measured results compared with the simulated results validated the proposed design.

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