Toll-like receptor expression on classic and pro-inflammatory blood monocytes after acute exercise in humans

Monocytes are a heterogeneous group of cells, the relative distribution of which change in peripheral blood following a strenuous bout of aerobic exercise. Monocyte subtypes can be identified in blood based on the cell surface expression of CD14 and CD16: classic (CD14^++bright/CD16^-negative) and the CD16^+dim (CD14^++bright/CD16^+dim) and CD16^++bright (CD14^+dim/CD16^++bright) pro-inflammatory subtypes. Whole monocyte population changes in TLR2, TLR4 and HLA.DR expression have previously been documented after acute exercise without accounting for relative changes in monocyte subpopulations, therefore, this study examined their expression on classic and pro-inflammatory monocyte subsets following 45 min of treadmill running at 75% over(V, ̇) O_{2 max}. Mononuclear cells isolated from the peripheral blood of moderately trained male subjects (n = 15) before (PRE), immediately after (POST) and 1 h after (1H) exercise were assessed for TLR2, TLR4 and HLA.DR expression on blood monocytes and their subpopulations using three-colour flow cytometry. Compared to PRE, the proportion of CD14⁺/CD16⁺ monocytes was 27% greater POST and 49% less at 1H and was associated with changes in the CD16^++bright pro-inflammatory subtype (p < 0.05). TLR2 expression was 12% lower on CD16^+dim monocytes POST (p < 0.05), whereas TLR4 and HLA.DR expression on total monocytes was 12% and 22% lower at 1H, respectively, and was attributed to changes in the classic (p < 0.05) and not the pro-inflammatory subsets (p > 0.05). We conclude that acute exercise causes localised changes in TLR2, TLR4 and HLA.DR expression within specific blood monocyte subpopulations, and could therefore be occurring at the cellular level. Such alterations might have significant implications for modulation of post-exercise immune surveillance.