BACKGROUND/AIMS: Immune responses are involved in arterial hypertension. An observational cross-sectional case control study was conducted to estimate the association between Toll-like receptor 4 (TLR4) expression and interleukin (IL)-17A serum levels in patients with controlled and non-controlled hypertension. METHODS: We have enrolled 105 non-complicated otherwise healthy hypertensive patients: 53 with well-controlled blood pressure and 52 non-controlled. TLR4 peripheral monocytes expression and serum IL-17A levels were determined by flow cytometry and ELISA, respectively. RESULTS: Non-controlled patients exhibited higher TLR4 expression than well-controlled (25.60 vs. 21.99, P=0.011). TLR4 expression was lower in well-controlled patients who were prescribed beta blockers (18.9 vs. 22.6, P=0.005) and IL-17A concentration was higher in patients using diuretics in either group (1.41 vs. 2.01 pg/ml, P<0.001; well-controlled 1.3 vs. 1.8 pg/ml, P= 0.023; non-controlled 1.6 vs. 2.3 pg/ml, P=0.001). Correlation between IL-17A concentration and hypertension duration was observed in non-controlled patients (Spearman correlation coefficient . ρ=0.566, P<0.001) whereas in well-controlled patients a correlation was found between hypertension duration and TLR4 expression (ρ=0.322, P=0.020). CONCLUSIONS: Arterial hypertension stimulates the immune response regardless of blood pressure regulation status. Prolonged hypertension influences peripheral monocyte TLR4 expression and IL-17A serum levels. Anti-hypertensive drugs have different immunomodulatory effects: diuretics are associated with higher IL-17A concentration and beta-blockers with lower TLR4 expression.