Animal Genetics Laboratory, Department of Nutrition, Genetics and Ethology, Faculty of Veterinary Medicine, Ghent University, Heidestraat 19, Merelbeke, Belgium.
Drug Quality and Registration (DruQuaR) Group, Faculty of Pharmaceutical Sciences, Ghent University, Ottergemsesteenweg 460, Ghent, Belgium.
J Dairy Sci. 2019 Feb;102(2):1457-1472. doi: 10.3168/jds.2018-15356. Epub 2018 Dec 26.
In neutrophils, toll-like receptor and complement component 5a (C5a) signaling are critical pathways regulating innate immunity. In cows, not much is known about the second C5a receptor, complement component 5a receptor 2 (C5AR2). It is an interesting player in sepsis treatment because it is considered to have an anti-inflammatory effect during normal inflammation. Periparturient cows are prone to severe infections, and the objectives of this study were to investigate the expression and functionality of C5AR2 during peripartum. We investigated the effect of 2 major inflammatory stimuli, C5a and lipopolysaccharide (LPS), on the expression of a selected number of genes (C5AR1, C5AR2, TLR4, ITGAM, COX2, and CXCL8) and functions linked to these receptors. Overall, TLR4, ITGAM, and C5AR2, all of which are involved in early inflammation, showed a lower expression in periparturient cows. However, an overall lower expression seems not to be the only explanation for the increased risk of sepsis in periparturient cows. Normally, in response to inflammation and as seen in the mid-lactation group, the expression of these genes increases after stimulation with LPS. However, in periparturient cows, stimulation with LPS led to a decrease in expression of these receptors, indicating a different response of neutrophils in response to LPS during this period. A decrease in ITGAM (coding for CD11b) expression complicates correct neutrophil localization and phagocytosis. Its downregulation upon stimulation might be detrimental for adequate eradication of the pathogen and might increase the risk of an imbalanced inflammation; C5AR2 seems to play a central role in this altered response. In addition, myeloperoxidase (MPO) activity in periparturient cows is lower in response to C5a stimulation. It has been suggested that MPO plays an important role in neutrophil shutdown and, thereby, timely resolution of inflammation. A decreased MPO activity might thus prolong the inflammatory reaction of the neutrophils. This finding was supported by the increased viability of the neutrophils obtained from periparturient cows. Even after stimulation, we found a lower caspase-3 activity in this group, indicating that they might be activated for a longer time compared with the neutrophils from mid-lactation cows. Accordingly, these alterations might contribute to a temporal mismatch in inflammatory responses, as often seen in severe periparturient infections.
在中性粒细胞中， Toll 样受体和补体成分 5a（C5a）信号通路是调节固有免疫的关键途径。在奶牛中，人们对第二种 C5a 受体，补体成分 5a 受体 2（C5AR2）知之甚少。它是治疗败血症的一个有趣的靶点，因为它在正常炎症中被认为具有抗炎作用。围产期奶牛容易发生严重感染，本研究的目的是研究 C5AR2 在围产期的表达和功能。我们研究了两种主要炎症刺激物，C5a 和脂多糖（LPS）对选定数量基因（C5AR1、C5AR2、TLR4、ITGAM、COX2 和 CXCL8）表达和与这些受体相关功能的影响。总的来说，TLR4、ITGAM 和 C5AR2 均参与早期炎症，在围产期奶牛中的表达水平较低。然而，对于围产期奶牛败血症风险增加，低表达似乎不是唯一的解释。通常情况下，在应对炎症时，正如泌乳中期组所见，这些基因在受到 LPS 刺激后表达增加。然而，在围产期奶牛中，LPS 的刺激导致这些受体的表达下降，表明在此期间中性粒细胞对 LPS 的反应不同。ITGAM（编码 CD11b）表达的下调会影响中性粒细胞的正确定位和吞噬作用。其在刺激时的下调可能不利于病原体的有效清除，并可能增加失衡炎症的风险；C5AR2 在这种改变的反应中似乎起着核心作用。此外，C5a 刺激时围产期奶牛的髓过氧化物酶（MPO）活性较低。有人提出 MPO 在中性粒细胞失活中起重要作用，从而及时缓解炎症。因此，MPO 活性的降低可能会延长中性粒细胞的炎症反应。这一发现得到了来自围产期奶牛的中性粒细胞活力增加的支持。即使在刺激后，我们发现该组中的 caspase-3 活性较低，这表明与泌乳中期奶牛的中性粒细胞相比，它们可能被激活更长时间。因此，这些改变可能导致炎症反应的时间不匹配，如严重围产期感染中经常发生的那样。
