Increased Inflammatory Low-Density Neutrophils in Morbid Obesity: Gene Expression and Effect of Bariatric Surgery

Background: Low-density neutrophils (LDN) are increased in several inflammatory diseases, and may also play a role in low-grade chronic inflammation in obesity. Yet their role in obesity or the effect of bariatric surgery-induced weight loss is unknown. Methods: We compared circulating LDN, their function, and gene expression between morbidly obese patients (MOP; BMI > 40 Kg/m2) and normal-weight controls (NWC; BMI < 25 Kg/m2) in a case-control study. Additionally, in a prospective longitudinal study, we measure changes in the frequency of LDN before and after bariatric surgery, and tested possible associations with metabolic and inflammatory parameters. Findings: LDN and inflammatory markers were significantly increased in MOP (n=27) compared to NWC (n=20). Transcriptome analysis of LDN from MOP showed an increased neutrophil-related gene expression signature associated with inflammation, neutrophil activation, and immunosuppressive function. However, LDN did not suppress T cells proliferation and produced low levels of ROS. Circulating LDN in MOP significantly decreased after surgery in parallel with BMI, metabolic syndrome and inflammatory markers. Interpretation: Obesity increases LDN with inflammatory gene signature. Bariatric surgery has anti-inflammatory effect including reduction of LDN. Gene expression and phenotype suggest that LDN represent a neutrophil subset that may be associated with obesity-associated chronic inflammation that promotes co-morbidities. Overall design: We did RNA-seq in circulating LDN from obese patients (n=8) and healthy weight controls (n=5). RNA was extracted, qualified by Agilent 2100 and quanitfied by qubit. Librarires were prepared using the Illumina's TruSeq Stranded mRNA kit and sequenced at 2 x 75bp (50M reads/sample). UPDATE: [Sept-23-2025] The genders were corrected.