Distinct neutrophil C5a receptor inflammatory events in cows initiated by chemoattractant C5a and lipopolysaccharide around parturition and in mid lactation

摘要

In neutrophils, toll-like receptor and complementcomponent 5a (C5a) signaling are critical pathwaysregulating innate immunity. In cows, not much isknown about the second C5a receptor, complementcomponent 5a receptor 2 (C5AR2). It is an interestingplayer in sepsis treatment because it is consideredto have an anti-inflammatory effect during normalinflammation. Periparturient cows are prone to severeinfections, and the objectives of this study were to investigatethe expression and functionality of C5AR2during peripartum. We investigated the effect of 2 majorinflammatory 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 earlyinflammation, showed a lower expression in periparturientcows. However, an overall lower expression seemsnot to be the only explanation for the increased risk ofsepsis in periparturient cows. Normally, in response toinflammation and as seen in the mid-lactation group,the expression of these genes increases after stimulationwith LPS. However, in periparturient cows, stimulationwith LPS led to a decrease in expression of these receptors,indicating a different response of neutrophilsin response to LPS during this period. A decrease inITGAM (coding for CD11b) expression complicatescorrect neutrophil localization and phagocytosis. Itsdownregulation upon stimulation might be detrimentalfor adequate eradication of the pathogen and might increasethe risk of an imbalanced inflammation; C5AR2seems to play a central role in this altered response. Inaddition, myeloperoxidase (MPO) activity in periparturientcows is lower in response to C5a stimulation. Ithas been suggested that MPO plays an important rolein neutrophil shutdown and, thereby, timely resolutionof inflammation. A decreased MPO activity might thusprolong the inflammatory reaction of the neutrophils.This finding was supported by the increased viabilityof the neutrophils obtained from periparturient cows.Even after stimulation, we found a lower caspase-3activity in this group, indicating that they might be activatedfor a longer time compared with the neutrophilsfrom mid-lactation cows. Accordingly, these alterationsmight contribute to a temporal mismatch in inflammatoryresponses, as often seen in severe periparturientinfections.