The objectives of this study were to evaluate the natural age-related variation and compare the level of pro-inflammatory cytokines in the peripheral blood and lower airways of horses. The mRNA expression of IL-1β, IL-6, IL-8 TNF-α TLR-4 in bronchoalveolar lavage (BAL) fluid and peripheral blood mononuclear cells (PBMC) were studied by quantitative real time polymerase chain reaction (PCR) and differential cell count cytology from 44 horses of different ages. A significant age-related increase was found for the mRNA expression of IL-6, IL-8, TLR-4 and TNF-α in stimulated BAL cells and for TNF-α in stimulated PBMC. Furthermore, a significant decrease was found in the mRNA expression of IL-1β and TNF-α in stimulated BAL cells compared to stimulated PBMC. In conclusion, continued low antigen exposure of horses in the pasture environment could lead to a tight regulation of mRNA gene expression in the airway space compared to the peripheral blood and favour an age-related accumulation of mRNA genes.