Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Purdue University, West Lafayette, IN, USA.
Department of Basic Medical Sciences, College of Veterinary Medicine, Purdue University, West Lafayette, IN, USA.
Sci Rep. 2023 Jan 27;13(1):1486. doi: 10.1038/s41598-023-27956-y.
Gram-negative bacterial septicemia is mediated through binding of lipopolysaccharide (LPS) to mammalian toll-like receptor protein 4 (TLR4). TLR4 and its cognate protein, myeloid differentiation factor 2 (MD2) form a heterodimeric complex after binding LPS. This complex induces a cascade of reactions that results in increased proinflammatory cytokine gene expression, including TNFα, which leads to activation of innate immunity. In horses, the immune response to LPS varies widely. To determine if this variation is due to differences in TLR4 or MD2, DNA from 15 healthy adult horses with different TNFα dynamics after experimental intravenous LPS infusion was sequenced across exons of TLR4 and MD2. Haplotypes were constructed for both genes using all identified variants. Four haplotypes were observed for each gene. No significant associations were found between either TNFα baseline concentrations or response to LPS and haplotype; however, there was a significant association (P value = 0.0460) between the baseline TNFα concentration and one MD2 missense variant. Three-dimensional structures of the equine TLR4-MD2-LPS complex were built according to haplotype combinations observed in the study horses, and the implications of missense variants on LPS binding were modeled. Although the sample size was small, there was no evidence that variation in TLR4 or MD2 explains the variability in TNFα response observed after LPS exposure in horses.
革兰氏阴性菌败血症是通过脂多糖（LPS）与哺乳动物 toll 样受体蛋白 4（TLR4）结合来介导的。TLR4 及其同源蛋白髓样分化因子 2（MD2）在结合 LPS 后形成异二聚体复合物。该复合物诱导一系列反应，导致促炎细胞因子基因表达增加，包括 TNFα，从而激活先天免疫。在马中，对 LPS 的免疫反应差异很大。为了确定这种变异是否是由于 TLR4 或 MD2 的差异引起的，对 15 匹在实验性静脉内 LPS 输注后具有不同 TNFα 动力学的健康成年马的 DNA 进行了 TLR4 和 MD2 外显子的测序。使用所有鉴定的变体为这两个基因构建了单倍型。每个基因观察到 4 种单倍型。未发现 TNFα 基线浓度或对 LPS 的反应与单倍型之间存在显著关联；然而，在基线 TNFα 浓度和一个 MD2 错义变体之间存在显著关联（P 值=0.0460）。根据在研究马匹中观察到的单倍型组合构建了马 TLR4-MD2-LPS 复合物的三维结构，并对 LPS 结合的错义变体进行了建模。尽管样本量较小，但没有证据表明 TLR4 或 MD2 的变异可以解释马在 LPS 暴露后观察到的 TNFα 反应的可变性。
