BACKGROUNDS: Interleukin (IL)-17 is a proinflammatory cytokine that is produced largely by a unique CD4(+) T-helper (Th) subset called Th17 cells. Recently, the novel IL-17 axis was investigated in acute coronary syndrome (ACS), and the level of expression of IL-17 was significantly higher in ACS. It is well known that the ACS is associated with different inflammation pathogenesis in the stable angina (SA). Thus, we analyzed the CD4+ Th17 and Th1 cell responses in coronary artery blood from patients with ACS and SA with the technique of flow cytometry manner. METHODS: Fourteen adult patients with ACS and 9 patients with SA were recruited. The clinical characteristics of these patients were checked. Coronary artery blood was sampled during conventional coronary angiography, and the mononuclear cells from patients were stimulated for 4 hours ex vivo with phorbol myristate acetate and ionomycin. The frequency of CD4(+) T cells producing IL-17 and/or IFN-gamma was measured by using flow cytometry. The hs-CRP level was also compared between ACS and SA patients. RESULTS: There was no significant difference in baseline characteristics including age, sex, and cardiovascular risk factors between 2 groups. The frequency of CD4(+)IFN-gamma(+) T cells was similar between the two groups (ACS: 19.1짹10.4%, SA: 23.8짹6.1%; p>0.05). However, patients with ACS had an decreased frequency of CD4(+)IL-17(+) T cells (1.7짹1.0%) compared with patients with SA (3.2짹1.0%, p<0.05). The ratio of IL-17(+)/IFN-gamma(+) was significantly lower in ACS group (0.09짹0.04) than in SA group (0.13짹0.04, p<0.05) indicating an altered balance of Th17 and Th1 cell responses in acute coronary syndrome. However, the hs-CRP level were not different between 2 groups (0.72짹1.8mg/dl;ACS, 1.62짹3.7mg/dl;SA, p>0.05). CONCLUSIONS: We showed Th17 cell response was more important in the pathogenesis of SA than in ACS. Our data also indicated that the mechanisms of inflammation involved in balancing Th1 and Th17 regulation was different between ACS and SA groups.