title: Sex differences in monocyte expression of IL-6: role of autonomic mechanisms.
abstract: Sex differences in the prevalence of inflammatory disorders exist, perhaps due to sex differences in cellular mechanisms that contribute to proinflammatory cytokine activity. This study analyzed sex differences of monocyte intracellular expression of IL-6 and its associations with reproductive hormones and autonomic mechanisms in 14 matched pairs of men and women (n = 28). Monocyte intracellular IL-6 production was repeatedly assessed over two circadian periods. Sympathetic balance was estimated by heart rate variability and the ratio of power in the low-frequency (LF) to high-frequency (HF); vagal tone was indexed by the power of HF component. As compared to men, women showed greater monocyte expression of IL-6 across the circadian period. In addition, women showed lower sympathetic balance (LF/HF ratio), and greater levels of vagal tone (HF power). In women, but not men, sympathovagal balance was negatively associated with monocyte IL-6 expression, whereas vagal tone was positively associated with production of this cytokine. Levels of reproductive hormones were not related to monocyte IL-6 expression. The marked increase in monocyte expression of interleukin-6 in women has implications for understanding sex differences in risk of inflammatory disorders. Additionally, these data suggest that sex differences in sympathovagal balance or vagal tone may be a pathway to explain sex differences in IL-6 expression. Interventions that target autonomic mechanisms might constitute new strategies to constrain IL-6 production with impacts on inflammatory disease risk in women.
authors.affiliation: Cousins Center for Psychoneuroimmunology, UCLA Semel Institute for Neuroscience and Human Behavior, University of California-Los Angeles, 300 Medical Plaza, Los Angeles, CA 90095-7076, USA. mfoconnor@mednet.ucla.edu
authors.forename: Mary-Frances
authors.initials: MF
authors.lastname: O'Connor
authors.forename: Sarosh J
authors.initials: SJ
authors.lastname: Motivala
authors.forename: Edwin M
authors.initials: EM
authors.lastname: Valladares
authors.forename: Richard
authors.initials: R
authors.lastname: Olmstead
authors.forename: Michael R
authors.initials: MR
authors.lastname: Irwin
mesh_terms: D000328:Adult; D001341:Autonomic Nervous System / Q000187:drug effects / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006728:Hormones / Q000097:blood; D006801:Humans; D015850:Interleukin-6 / Q000096:biosynthesis*; D008070:Lipopolysaccharides / Q000494:pharmacology; D008297:Male; D008875:Middle Aged; D009000:Monocytes / Q000187:drug effects / Q000378:metabolism*; D010275:Parasympathetic Nervous System / Q000502:physiology; D012727:Sex Characteristics; D013564:Sympathetic Nervous System / Q000502:physiology; D051197:Toll-Like Receptor 4 / Q000187:drug effects / Q000378:metabolism; D014630:Vagus Nerve / Q000502:physiology
chemical_list: D006728:Hormones; D015850:Interleukin-6; D008070:Lipopolysaccharides; D051197:Toll-Like Receptor 4