Heme oxygenase-1 restores impaired GARPCD4 + CD25 + regulatory t cells from patients with acute coronary syndrome by upregulating LAP and GARP expression on activated t lymphocytes

Abstract

Background: Accumulating evidence shows that the pathological autoreactive immune response is responsible for plaque rupture and the subsequent onset of acute coronary syndrome (ACS). Naturally occurring CD4 + CD25 + regulatory T cells (nTregs) are indispensable in suppressing the pathological autoreactive immune response and maintaining immune homeostasis. However, the number and the suppressive function of glycoprotein-A repetitions predominant (GARP) + CD4 + CD25 + activated nTregs were impaired in patients with ACS. Recent evidence suggests that heme oxygenase-1 (HO-1) can regulate the adaptive immune response by promoting the expression of Foxp3. We therefore hypothesized that HO-1 may enhance the function of GARP + CD4 + CD25 + Tregs in patients with ACS and thus regulate immune imbalance. Methods: T lymphocytes were isolated from healthy volunteers (control, n=30) and patients with stable angina (SA, n=40) or ACS (n=51). Half of these cells were treated with an HO-1 inducer (hemin) for 48 h, and the other half were incubated with complete RPMI-1640 medium. The frequencies of T-helper 1 (Th1), Th2, Th17 and latency-associated peptide (LAP) + CD4 + T cells and the expression of Foxp3 and GARP by CD4 + CD25 + T cells were then assessed by measuring flow cytometry after stimulation in vitro. The suppressive function of activated Tregs was measured by thymidine uptake. The levels of transforming growth factor-1 (TGF-β1) in the plasma were measured using enzyme-linked immunosorbent assay (ELISA). The expression levels of the genes encoding these proteins were analyzed by real-time polymerase chain reaction. Results: Patients with ACS exhibited an impaired number and suppressive function of GARP + CD4 + CD25 + Tregs and a mixed Th1/Th17-dominant T cell response when compared with the SA and control groups. The expression of LAP in T cells was also lower in patients with ACS compared to patients with SA and the control individuals. Treatment with an HO-1 inducer enhanced the biological activity of GARP + CD4 + CD25 + Tregs and resulted in increased expression of LAP and GARP by activated T cells. Conclusion: The reduced number and impaired suppressive function of GARP + CD4 + CD25 + Tregs result in excess effector T cell proliferation, leading to plaque instability and the onset of ACS. HO-1 can effectively restore impaired GARP + CD4 + CD25 + Tregs from patients with ACS by promoting LAP and GARP expression on activated T cells.