Soluble TNFR1 has greater reproducibility than IL-6 for the assessment of chronic inflammation in older adults: the case for a new inflammatory marker in aging.

Chronic inflammatory pathway activation, commonly referred to as "Inflammaging" or chronic inflammation (CI), is associated with frailty, cognitive and functional decline, and other causes of health span decline in older adults. We investigated the variability of candidate serum measures of CI among community-dwelling older adults selected for mild low-grade inflammation. We focused on serum cytokines known to be highly predictive of adverse health outcomes in older adults (sTNFR1, IL-6) during a short-term (weeks) and medium-term (months) follow-up, as well as immune markers that are less studied in aging but reflect other potentially relevant domains such as adaptive immune activation (sCD25), innate immune activation (sCD14 and sCD163), and the inflammation-metabolism interface (adiponectin/Acrp30) during short-term (weeks) follow up. We found that sTNFR1 was more reproducible than IL-6 over a period of weeks and months short-term and medium-term. The intra-class correlation coefficient (ICC) for sTNFR1 was 0.95 on repeated measures over 6 weeks, and 0.79 on repeated measures with mean interval of 14 weeks, while the ICC for IL-6 was 0.52 over corresponding short-term and 0.67 over corresponding medium-term follow-up. This suggests that sTNFR1 is a more reliable marker of CI than IL-6. This study provides new insights into the reproducibility of serum markers of CI in older adults. The findings suggest that sTNFR1 may be a better marker of CI than IL-6 in this population. Further studies are needed to confirm these findings and to investigate the clinical utility of sTNFR1 in older adults.