The Role Of PD-1/PD-L Pathway On Immune Modulation During The Process Of Atrial Fibrillation

Atrial fibrillation (atrial fibrillation, AF) is the most common clinicallyarrhythmia. However, the pathophysiology of AF is not entirely clear. Recently,increasing evidence supports the influence of immune-mediated inflammatoryresponse in the pathogenesis of AF. It has been established that serum or plasmainflammation biomarkers including CRP and IL-6et al. and some autoantibodiessuch as anti-M2muscarinic receptor autoantibodies et al. increase in patients withAF, and activated T-lymphocytes infiltrate the endomyocardial in AF patients.However, there is no sufficient evidence to clarify the molecular mechanism ofimmune response or regulation in this process.T cell activation requires the classic dual signal. The first signal is a signalfrom the combination of TCR and MHC. APC or target cells link with theauxiliary molecules of T cells could provide the second signal. The represent-atives of the first signal molecules are CD69and HLA-DR et al. CD69, known asan early activation marker of lymphocytes, is a type II transmembraneglucoprotein. HLA-DR belongs to the MHC class II system which is known as alate activation marker of lymphocytes. It is required for antigen presentation andactivation of helper T-lymphocytes. The up-regulation of CD69and HLA-DR will provide the first signal which could adjust activate of T cells.Pathways in the B7:CD28family have key roles in regulating T cellactivation and tolerance. These pathways not only provide critical positive secondsignals that promote and sustain T cell responses, but they also contribute criticalnegative second signals that downregulate T cell responses. Therefore, it wasbelieved to play a key balancing role in the process of immune activation.Previous studies have found that B7:CD28family mainly inhibits T cellactivation. Attention has been paid to PD-1/PD-L pathway due to the uniquesuppression role. Engagement of PD-1by its ligands (PD-L), PD-1always playsa role in inhibiting the activation of T cells. Interferons α, β, and γ are potentupregulators of PD-L1expression which could stimulate the expression of PD-L1on APCs. Now, PD-1/PD-L pathway is thought to play an important role inregulating T cells response and it has been extensively researched inautoimmunity disease and infectious disease. The expression of PD-L1andPD-L2at high levels in the heart suggests a role for PD-1/PD-L pathway play arole in cardiovascular disease. Now, PD-1/PD-L pathway has been investigated incoronary atherosclerotic heart disease, autoimmune myocarditis and dilatedcardiomyopathy but not AF. Up to now, whether PD-1/PD-L pathway participatesin the development of AF and T cell activation is involved in the pathogenesis ofAF have not been reported.In order to clarify whether the activation of T cells participate in theprogress of AF, we studied the expression profiles of CD69and HLA-DR onCD3+T cells, the expression profiles of PD-1on CD4+and CD8+T cells, theexpression profiles of PD-L on mDCs, macrophage, CD4+and CD8+T cells, andplasma concentrations of IL-2, IL-4, IL-6, IL-10, IL-17A, TNF and IFN-γinpatients with AF. Allogeneic mixed leukocyte reactions was used to evaluate the relation of PD-L changes and T cells proliferation while interferon-a (IFN-a)interfere with the expression of PD-L1as a stimulus. This study completed fouraspects of work:1Sample collection and analysis of CD69and HLA-DR expression oncirculating T cellsThe patients with a diagnosis of AF were enrolled in our study, which weredivided into two groups: the paroxysmal AF group and the persistent AF group.The volunteers with no history of arrhythmias served as control group. Bloodsample and clinical data from each patient were collected. CD69and HLA-DRexpression on circulating T cells were analyzed by flow cytometry.2Analysis of PD-1and PD-L expression on circulating blood cellsPD-1expression on CD4+and CD8+T cells, PD-L1and PD-L2expressionon mDCs, macrophage, CD4+T cells and CD8+T cells were analyzed by flowcytometry.3Analysis of plasma concentration of IL-2, IL-4, IL-6, IL-10, IL-17A, TNF andIFN-γPlasma concentration of IL-2, IL-4, IL-6, IL-10, IL-17A, TNF and IFN-γwere analyzed by CBA.4The impact of the PD-1/PD-L1pathway on the T-lymphocyte immune functionin AF patientsCD4+, CD8+T-lymphocyte and mDCs were isolated. Matured mDCs fromAF patients and control group were mixed with isolated CD4+or CD8+T-lymphocyte from a third healthy individual with or without IFN-a, anupregulator of PD-L1. Allogeneic mixed leukocyte reactions (MLR) andtritiated thymidine (3H-TdR) were performed to investigate the stimulatoryability of mDCs on the proliferation of T cells and the secretion of cytokine. Results:1The expression of CD69and HLA-DR on circulating CD3+T cells weresignificantly up-regulated compared with control group.2The expression of PD-1on CD4+T cells and the expression of PD-L1onmDCs were all significantly down-regulated compared with control group.Persistent AF group was more obvious than paroxysmal AF group.3The plasma concentration of IL-2, IL-6, IL-10and IFN-γwere all significantlyincreased. Persistent AF group was more obvious than paroxysmal AF group.There were not statistically difference in plasma concentration of IL-4, IL-17Aand TNF.4The stimulatory ability of mDCs from AF group on the proliferation of T cellsand the secretion of cytokine were significantly increased than mDCs fromcontrol group. However, the stimulatory ability of mDCs from AF group on theproliferation of T cells and the secretion of cytokine were significantly decreasedafter the stimulation of PD-L1expression by IFN-α.Conclusions:1The PD-1/PD-L1pathway participates in immune regulation of AF by CD4+Tcells and mDCs. The down-regulation of PD-1/PD-L1is closely related with theactivation of T cell and increased secretion of inflammatory cytokine in AFpatients.2The first signal molecules (CD69and HLA-DR) which might stimulateactivation of T cells are up-regulated, and the second signal molecules(PD-1/PD-L1) which might inhibite activation of T cells are down-regulated. Itsuggests that inflammation with characteristic of T cells activation may play a role in the pathophysiology of AF.