Altered neutrophil signalling linked to impaired chemotaxis and increased ROS and NET production in older people with...

Immune function alters with age, and is often accompanied by low-grade inflammation (inflammageing). In individuals with frailty, inflammageing is increased, dysregulating immune function and increasing susceptibility to serious outcomes from infection. In this study, we investigated the changes that take place in human neutrophils during healthy ageing and ageing with frailty (FR) using RNAseq and functional assays. We also compared neutrophil phenotype in frailty with rheumatoid arthritis (RA). RNAseq data were analysed using IDEP2 and Ingenuity Pathway Analysis (IPA). Neutrophil phenotype was assessed for reactive oxygen species (ROS) production, neutrophil extracellular trap (NET) release, chemotaxis, and bacterial killing capacity. Experimental data were analysed by ANOVA in R (v4.5.1). RNAseq identified activation of G-protein coupled receptors, interferon and cytokine receptor signalling, and chemotaxis pathways in frail individuals (n = 10) compared with healthy older (n = 9) and healthy younger people (n = 8, adj. P < 0.05). FR neutrophils expressed more IL-8 receptors (CXCR1 and CXCR2) and CD177 on their surface (n = 5-8, P < 0.05). FR and RA neutrophils released significantly more ROS (n = 6-7) and had impaired chemotaxis (n = 8-9) and bacterial killing capacity (n = 5, P < 0.05) compared with both healthy groups. FR neutrophils also released significantly more NETs in response to LPS (10 ng/ml, n = 6-7, P < 0.05). This work provides novel insight into the altered neutrophil phenotype associated with ageing in good health and ageing with frailty, and highlights similarities between inflammageing in frailty and chronic inflammation in RA. This may be important in the development of therapeutics and/or health management strategies to support healthy living as we age.