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Am J Physiol Regul Integr Comp Physiol 293: R145-R151, 2007. First published April 11, 2007; doi:10.1152/ajpregu.00752.2006
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INFLAMMATION AND CYTOKINES

Sex differences in monocyte expression of IL-6: role of autonomic mechanisms

Mary-Frances O'Connor, Sarosh J. Motivala, Edwin M. Valladares, Richard Olmstead, and Michael R. Irwin

Cousins Center for Psychoneuroimmunology, University of California, Los Angeles, Semel Institute for Neuroscience and Human Behavior, Los Angeles, California

Submitted 27 October 2006 ; accepted in final form 21 March 2007

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.

vagal; heart rate variability; inflammatory disorders; proinflammatory cytokines; sympathetic


Address for reprint requests and other correspondence: M.-F. O'Connor, Cousins Center for Psychoneuroimmunology, UCLA Semel Institute for Neuroscience and Human Behavior, 300 Medical Plaza, Rm. 3156, Los Angeles, CA 90095-7076 (e-mail: mfoconnor{at}mednet.ucla.edu)






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