Is the IL1RA/IL1B Ratio a Suitable Biomarker for Subclinical Endometritis in Dairy Cows?

SIMPLE SUMMARY: Chronic inflammation in the uterus after calving leads to reduced fertility in dairy cows, resulting in huge economic losses for dairy farmers as well as the premature removal of impacted animals. Correctly identifying and diagnosing affected cows allows for the appropriate and timely treatment of the condition. This study aimed to compare the concentrations of two factors associated with the early immune response in secretions collected from the uterus of cows with and without chronic uterine inflammation. One of these factors is known to cause (further) inflammation while its counterpart generally reduces inflammation in tissues. We found that the factor increasing inflammation was present in significantly higher concentrations in the uterus of cows diagnosed with prolonged uterine inflammation compared with cows without the inflammation. The factor reducing inflammation was present in similar concentrations in both groups of cows, but the ratio of the two measured proteins also differed between healthy and diseased cows. In conclusion, this study highlights the importance of the two measured immune factors in the development of inflammation in the uterus, as well as their potential as a diagnostic tool. ABSTRACT: The adequate expression of cytokines is essential for the prevention and healing of bovine endometrial inflammation. This study investigated the intra-uterine concentration of the proinflammatory cytokine interleukin (IL)1B and its antagonist IL1RA in cows with and without subclinical endometritis (SE). Samples were taken from 37 uteri at the abattoir and 26 uteri in vivo. Uterine secretion samples were classified as showing no signs of SE (SEneg; polymorphonuclear neutrophil granulocyte (PMN) < 5%) or showing signs of SE (SEpos; PMN ≥ 5%). Concentrations and ratios for IL1B and IL1RA were measured using a commercial and a newly established AlphaLISA kit, respectively. In both groups, a higher concentration of IL1B was detected in the SEpos group compared with the SEneg group (abattoir: p = 0.027; in vivo p < 0.001). No significant differences were observed in the concentration of IL1RA (p > 0.05). In uterine secretion samples retrieved in vivo, a lower IL1RA/IL1B ratio was detected in the SEpos group compared with the SEneg group (p = 0.002). The results of this study highlight the important role of IL1B and IL1RA during endometritis and the potential of the IL1RA/IL1B ratio as a possible biomarker for SE.