The influence of prolonged cycling on monocyte Toll-like receptor 2 and 4 expression in healthy men

Several studies have reported that some immune cell functions including monocyte Toll-like receptor (TLR) expression and antigen presentation are temporarily impaired following acute bouts of strenuous exercise, which could represent an ‘open window’ to upper respiratory tract infection (URTI). However, we do not know the time course of effects of acute exercise on human monocyte TLR expression. The purpose of the present study was to examine the effects of 1.5 h cycling at 75% VO_2peak on human monocyte TLR2 and TLR4 expression and how long it takes for TLR expression to return to pre-exercise values. Nine healthy endurance trained males (age 25 ± 5 years) had blood samples taken before and for up to 24 h after exercise and analysed using flow cytometry. Although there was an increase in the total monocyte cell count at 0, 1 and 4 h post-exercise (P < 0.01), exercise reduced monocyte TLR4 expression (geometric mean fluorescence intensity, corrected for non-specific binding; P < 0.05) by 32 and 45% at 0 and 1 h post-exercise, respectively, compared with pre-exercise values but had returned to baseline values by 4 h post-exercise. There were no statistically significant changes in TLR2 expression after exercise. In addition, a control resting study was conducted on six healthy endurance trained men (age 25 ± 2 years) to analyse any diurnal changes on monocyte TLR2 and TLR4 expression but no changes were found across time (P > 0.05). This study showed that prolonged cycling at 75% VO_2peak temporarily reduces TLR4 expression, which may in part be responsible for post-exercise immunodepression.