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1 School of Sport and Exercise Sciences
2 Department of Immunology, The Medical School, University of Birmingham, Birmingham, UK
3 GlaxoSmithKline Consumer Healthcare
4 School of Sport and Exercise Sciences, Loughborough University, Loughborough, UK
Eleven mammalian toll-like receptors (TLRs 111) have been identified to date and are known to play a crucial role in the regulation of immune responses; however, the factors that regulate TLR expression and function in vivo are poorly understood. Therefore, in the present study, we investigated the physiological regulation of TLR expression and function in humans. To examine the influence of diurnal rhythmicity on TLR expression and function, peripheral venous blood samples were collected from healthy volunteers (n = 8) at time points coinciding with the peak and nadir in the endogenous circulating cortisol concentration. While no diurnal rhythmicity in the expression of TLRs 1, 2, 4 or 9 was observed, the upregulation of costimulatory (CD80 and CD86) and antigen-presenting (MHC class II) molecules on CD14+ monocytes following activation with specific TLR ligands was greater (P < 0.05) in samples obtained in the evening compared with the morning. To examine the influence of physical stress on TLR expression and function, peripheral venous blood samples were collected from healthy volunteers (n = 11) at rest and following 1.5 h of strenuous exercise in the heat (34°C). Strenuous exercise resulted in a decrease (P < 0.005) in the expression of TLRs 1, 2 and 4 on CD14+ monocytes. Furthermore, the upregulation of CD80, CD86, MHC class II and interleukin-6 by CD14+ monocytes following activation with specific TLR ligands was decreased (P < 0.05) in samples obtained following exercise compared with at rest. These results demonstrate that TLR function is subject to modulation under physiological conditions in vivo and provide evidence for the role of immunomodulatory hormones in the regulation of TLR function.
(Received 13 December 2004;
accepted after revision 15 January 2005;
first published online 20 January 2005)
Corresponding author G. Lancaster: RMIT University, School of Medical Sciences, Division of Biosciences, Bundoora Campus, PO Box 71, Bundoora 3083, Victoria, Australia. Email: graeme.lancaster{at}rmit.edu.au
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