title: Circulating muramyl dipeptide is negatively associated with interleukin-10 in the frail elderly.
abstract: Elevated levels of serum cytokines, a marker of immune activation and chronic inflammation, are commonly associated with age and are a significant risk factor for all-cause mortality in the elderly. This phenomenon is very similar to that exhibited by individuals with diseases of inflammatory etiology and chronic viral infections such as human immunodeficiency virus (HIV). Although the origin of chronically elevated cytokines with age is unknown, for chronic diseases and viral infections, a role for circulating bacterial products and other pattern recognition receptor (PRR) ligands has been suggested. Given this, we sought to examine whether the levels of circulating cytokines (tumour necrosis factor (TNF), interferon-gamma (IFN-γ), interleukin (IL)-1β, IL-6, IL-8, IL-10, IL-12) in the advanced-age, frail elderly (n = 135) correlated with plasma levels of lipopolysaccharide (LPS), muramyl dipeptide (MDP), 16S ribosomal DNA, total cell-free DNA and host-derived mitochondrial DNA. After adjusting for multiple testing, no associations between circulating products and donor age, sex or comorbidities were observed. However, a significant negative correlation between MDP and IL-10 was identified. Given the anti-inflammatory nature of IL-10, a negative relationship with a potent inflammatory agonist such as MDP is not surprising and suggests a potential role for circulating MDP in the propagation of age-related immune activation.
authors.affiliation: Department of Pathology and Molecular Medicine, McMaster University, MDCL 4020 1280 Main Street West, Hamilton, ON, L8S 4K1, Canada.
authors.forename: Chris P
authors.initials: CP
authors.lastname: Verschoor
authors.forename: Avee
authors.initials: A
authors.lastname: Naidoo
authors.forename: Jessica G
authors.initials: JG
authors.lastname: Wallace
authors.forename: Jennie
authors.initials: J
authors.lastname: Johnstone
authors.forename: Mark
authors.initials: M
authors.lastname: Loeb
authors.forename: Jonathan L
authors.initials: JL
authors.lastname: Bramson
authors.forename: Dawn Me
authors.initials: DM
authors.lastname: Bowdish
mesh_terms: D000119:Acetylmuramyl-Alanyl-Isoglutamine / Q000097:blood*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015415:Biomarkers / Q000097:blood; D015331:Cohort Studies; D005260:Female; D016330:Frail Elderly; D006801:Humans; D016753:Interleukin-10 / Q000097:blood*; D008297:Male; D008875:Middle Aged; D055815:Young Adult
chemical_list: D015415:Biomarkers; D016753:Interleukin-10; D000119:Acetylmuramyl-Alanyl-Isoglutamine