Autoantigen Estimation and Simple Screening Assay Against Cardiodepressant Autoantibodies in Patients With Dilated Cardiomyopathy

Anti-cardiac troponin antibodies in clinical human disease: a systematic review

Anti-cardiac troponin antibodies have been studied in different types of clinical diseases and in healthy populations. A systematic review of published data on anti-troponin antibodies was carried out (search performed on PubMed, ISI Web of Knowledge and Scopus databases). From title and abstract analysis, thirty-three articles were included that met the pre-specified criteria; after full-text analysis, nine articles were excluded. Most studies assessed anti-troponin I antibodies. The prevalence of anti-cardiac troponin antibodies in healthy individuals ranged from 0.0% to 20.0%. The prevalence of anti-troponin I autoantibodies in dilated cardiomyopathy (DCM) ranged from 7.0% to 22.2%. Other conditions under study were myocardial infarction, ischemic cardiomyopathy (ICM), peripartum cardiomyopathy (PPCM), Chagas disease, Emery-Dreifuss muscular dystrophy (EDMD) and renal transplantation. In the different patient populations studied, anti-cardiac troponin antibodies have been shown to be either positively or negatively associated with prognostic and clinical features. In what concerns a possible value as biomarkers, these assays have not emerged up to the present moment as important aids for practical clinical decisions in cardiac or other types of patients. In what concerns pathophysiology, anti-cardiac troponin autoantibodies may play a role in different diseases. It can be speculated that these antibodies could be involved in perpetuating some degree of cardiac injury after an event, such as myocardial infarction or PPCM.

Myocardial Recovery in Patients With Systolic Heart Failure and Autoantibodies Against β1-Adrenergic Receptors

BACKGROUND

Among various cardiac autoantibodies (AAbs), those recognizing the β₁-adrenergic receptor (β₁AR) demonstrate agonist-like effects and induce myocardial damage that can be reversed by β-blockers and immunoglobulin G3 (IgG3) immunoadsorption.

OBJECTIVES

The goal of this study was to investigate the role of β₁AR-AAbs belonging to the IgG3 subclass in patients with recent-onset cardiomyopathy.

METHODS

Peripheral blood samples were drawn at enrollment in patients with recent-onset cardiomyopathy (left ventricular ejection fraction [LVEF] ≤0.40; <6 months). The presence of IgG and IgG3-β₁AR-AAb was determined, and echocardiograms were assessed, at baseline and 6 months. Patients were followed up for ≤48 months.

RESULTS

Among the 353 patients who had blood samples adequate for the analysis, 62 (18%) were positive for IgG3-β₁AR-AAbs (IgG3 group), 58 (16%) were positive for IgG but not IgG3 (non-IgG3 group), and the remaining were negative. There were no significant differences in baseline systolic blood pressure, heart rate, or LVEF among the groups at baseline. Left ventricular end-diastolic and end-systolic diameters were significantly larger in the non-IgG3 group compared with the other groups (left ventricular end-diastolic diameter, p < 0.01; left ventricular end-systolic diameter, p = 0.03). At 6 months, LVEF was significantly higher in the IgG3 group (p = 0.007). Multiple regression analysis showed that IgG3-β₁AR-AAb was an independent predictor of LVEF at 6 months and change in LVEF over 6 months, even after multivariable adjustment (LVEF at 6 months, β = 0.20, p = 0.01; change in LVEF, β = 0.20, p = 0.008). In patients with high New York Heart Association functional class (III or IV) at baseline, the IgG3 group had a lower incidence of the composite endpoint of all-cause death, cardiac transplantation, and hospitalization due to heart failure, whereas the non-IgG3 group had the highest incidence of the composite endpoint.

CONCLUSIONS

IgG3-β₁AR-AAbs were associated with more favorable myocardial recovery in patients with recent-onset cardiomyopathy.

Autoantibodies Specifically Against β1 Adrenergic Receptors and Adverse Clinical Outcome in Patients With Chronic Systolic Heart Failure in the β-Blocker Era: The Importance of Immunoglobulin G3 Subclass

OBJECTIVE

To elucidate the prevalence and role of β1 adrenergic receptor autoantibodies (β1AR-AAb) belonging to the immunoglobulin (Ig)G3 subclass in patients with heart failure (HF) treated with β-adrenergic blockers.

BACKGROUND

Several cardiac AAbs have been reported to be present in sera from patients with dilated cardiomyopathy and other etiologies. Among AAbs, those recognizing β1AR-AAbs show agonist-like effects, have detrimental effects on cardiomyocytes, and may induce persistent myocardial damage.

METHODS

We quantify total IgG and IgG3 subclass β1AR-AAb in subjects with chronic stable HF with long-term follow-up.

RESULTS

In our study cohort of 121 subjects, non-IgG3-β1AR-AAb and IgG3-β1AR-AAb were found to be positive in 20 (17%) and 26 patients (21%), respectively. The positive rate of IgG3-β1AR-AAb was significantly higher for those with nonischemic compared with ischemic HF etiology (27% vs 8%, P = .01), but the positive rate for non-IgG3-β1AR-AAb was similar between the 2 groups (18% vs 16%, respectively, P = NS). There were no significant differences in clinical and echocardiographic measures among total β1AR-AAb negative, non-IgG3-β1AR-AAb positive, and IgG3-β1AR-AAb positive groups at baseline. During 2.2 ± 1.2 years of follow-up, we observed similar rates of the composite endpoint of all-cause mortality, cardiac transplantation, or hospitalization resulting from HF between total IgG-β1AR-AAb negative and positive patients. However, the composite endpoint events were significantly more common in the patients without than in those with IgG3-β1AR-AAb (P = .048, log-rank test).

CONCLUSIONS

Presence of IgG3-β1AR-AAb, not total IgG, was associated with paradoxically more favorable outcomes in our cohort of patients with chronic systolic HF largely treated by β-blockers.

Autoantibodies and cardiovascular dysfunction: cause or consequence?

There has been a long history of the exploration into autoimmunity as a possible pathogenic factor of cardiovascular diseases from unknown cause represented by dilated cardiomyopathy (DCM). Autoantibodies (AAbs) have emerged either as humoral responses provoked by the release of "self-antigens" due to tissue damage or dysregulated humoral immunity itself. The pathogenic roles of some AAbs have been suggested by the findings from basic research using in vitro and in vivo disease models as well as clinical studies including immunoadsorption studies removing AAbs from patients with DCM. In this context, the importance of AAbs belonging to IgG3 subclass has also been implicated. In this review article, we summarize the findings accumulated to date regarding AAbs which have been considered to be involved in the pathology of DCM or pregnancy-related cardiovascular disease. Furthermore, we discuss the significance of AAbs as a possible cause of DCM and their potential roles as a novel therapeutic target.

Cardiac involvements in myasthenia gravis associated with anti-Kv1.4 antibodies

BACKGROUND AND PURPOSE

There is no general consensus as to whether autoimmune myasthenia gravis (MG) is associated with heart diseases, despite the fact that myocarditis, a serious cardiac involvement treatable by immunotherapy, is a complication of MG. It has been observed previously that MG patients with clinically suspected myocarditis had anti-Kv1.4 antibodies. The purpose of this study was to disclose the association between anti-Kv1.4 antibodies and cardiac involvements in MG patients.

METHODS

Anti-Kv1.4 antibody was detected by an immunoprecipitation assay using (35) S-labeled rhabdomyosarcome cellular extract as the antigen source. Cardiac findings including electrocardiography (ECG) and clinical features of clinically suspected myocarditis in MG patients with anti-Kv1.4 antibodies were investigated. Ultrasound echocardiography (UCG) of ex vivo chick embryos was performed to determine the suppressive effects of sera with or without anti-Kv1.4 antibodies on heart muscle functions.

RESULTS

Seventy (10.8%) of 650 MG patients had anti-Kv1.4 antibodies and 60% of them had abnormal ECG findings with high frequencies of T-wave abnormality and QT prolongation. Clinically suspected myocarditis was found in eight MG patients with anti-Kv1.4 antibodies but in none of the MG patients without anti-Kv1.4 antibodies. Most patients showed rapid deterioration with lethal arrhythmias such as ventricular tachycardia, sick sinus syndrome, or complete atrial ventricular block and severe heart failure. It was concluded using UCG of ex vivo chick embryos that MG serum with anti-Kv1.4 antibodies suppressed heart muscle functions.

CONCLUSION

It has been demonstrated that anti-Kv1.4 antibodies are possible markers for cardiac involvements in MG patients.

Analysis of IL-17 gene polymorphisms in Chinese patients with dilated cardiomyopathy

Cardiomyopathy is one of the major causes of sudden death and/or progressive heart failure. Dilated cardiomyopathy (DCM), comprising 60% of the cases of identified cardiomyopathy, is the most common form of heart muscle disease. Interleukin 17 (IL-17) is a proinflammatory cytokine that has been implicated in the pathogenesis of various diseases. To evaluate the influence of IL-17A and IL-17F gene polymorphisms on the risk of DCM, a case-control study was conducted in a Chinese Han population. The TaqMan® SNP Genotyping Assay was used to genotype the SNP rs2275913 of IL-17A and SNP rs763780 of IL-17F in 288 DCM patients and 421 ethnicity-matched controls. No significant difference in genotypic and allelic frequencies between DCM patients and control subjects was observed. However, Results of stratified analysis revealed that rs763780 was associated with male DCM patients in a dominant genetic model (p=0.031, OR=1.83, 95% CI=1.04-3.22). Our results suggest that the tested two IL-17 SNPs, rs2275913 and rs763780, are not found to be associated with DCM in the Chinese population studied.

Detection of anti-β1-AR autoantibodies in heart failure by a cell-based competition ELISA

RATIONALE

Autoantibodies directed against the second extracellular loop of the cardiac β1-adrenergic receptor (β1-AR) are thought to contribute to the pathogenesis of dilated cardiomyopathy (DCM) and Chagas heart disease. Various approaches have been used to detect such autoantibodies; however, the reported prevalence varies largely, depending on the detection method used.

OBJECTIVE

We analyzed sera from 167 DCM patients (ejection fraction<45%) and from 110 age-matched volunteers who did not report any heart disease themselves, with an often used simple peptide-ELISA approach, and compared it with a novel whole cell-based ELISA, using cells expressing the full transgene for the human β1-AR. Additionally, 35 patients with hypertensive heart disease with preserved ejection fraction were investigated.

METHODS AND RESULTS

The novel assay was designed according to the currently most reliable anti-TSH receptor antibody-ELISA used to diagnose Graves disease ("third-generation assay") and also detects the target antibodies by competition with a specific monoclonal anti-β1-AR antibody (β1-AR MAb) directed against the functionally relevant β1-AR epitope. Anti-β1-AR antibodies were detected in ≈60% of DCM patients and in ≈8% of healthy volunteers using the same cutoff values. The prevalence of these antibodies was 17% in patients with hypertensive heart disease. Anti-β1-AR antibody titers (defined as inhibition of β1-AR MAb-binding) were no longer detected after depleting sera from IgG antibodies by protein G adsorption. In contrast, a previously used ELISA conducted with a linear 26-meric peptide derived from the second extracellular β1-AR loop yielded a high number of false-positive results precluding any specific identification of DCM patients.

CONCLUSIONS

We established a simple and efficient screening assay detecting disease-relevant β1-AR autoantibodies in patient sera yielding a high reproducibility also in high throughput screening. The assay was validated according to "good laboratory practice" and can serve as a companion biodiagnostic assay for the development and evaluation of antibody-directed therapies in antibody-positive heart failure.

Cellular proliferative response to cardiac troponin-I in patients with idiopathic dilated cardiomyopathy

BACKGROUND

Approximately 20% of patients with idiopathic dilated cardiomyopathy (iDCM) have autoantibodies (AAbs) specific to cardiac troponin-I (cTnI). However, there has been no work evaluating active cellular autoimmunity. We aimed to identify a cTnI-stimulated cellular autoimmune response and to correlate our findings with cTnI AAb production.

METHODS

Samples were obtained from stable ambulatory iDCM patients and healthy controls. Peripheral blood monocytes were incubated with cTnI, and cellular proliferation was measured using flow cytometry. AAbs against cTnI were detected by enzyme-linked immunosorbent assay.

RESULTS

A positive cellular proliferative response to cTnI was identified in 20.5% (9/44) patients with iDCM and 5.7% (2/35) of healthy controls (p < 0.05). Positive cTnI AAbs were identified in 20% (7/35) of healthy controls and 13.6% (6/44) of patients with iDCM (p = NS). The presence of cTnI AAbs did not correlate with a positive cellular proliferative response. However, patients with iDCM who had an AAb response to cTnI were less likely to be taking a statin (p < 0.05).

CONCLUSIONS

A cellular autoimmune response to cTnI is demonstrated in a subset of patients with iDCM. However, the presence of a cellular response did not correlate with the presence of AAbs to the same antigen.

Specific immunoadsorption therapy using a tryptophan column in patients with refractory heart failure due to dilated cardiomyopathy

BACKGROUND

Certain cardiac-specific autoantibodies found in patients with dilated cardiomyopathy (DCM) play a role in mediating myocardial damage and fatal ventricular arrhythmias resulting in sudden cardiac death. Immunoadsorption therapy (IA) is one of the therapeutic tools to remove such autoantibodies. Clinical studies from Germany have shown that nonspecific IA using columns loaded by sheep antihuman IgG or protein A improved hemodynamic data and affected favorably cardiac function and survival in patients with heart failure (HF) due to DCM. The goal of this study is to determine if IA therapy using the high-profile tryptophan column, which has high affinity for IgG3 subclass, affects favorably cardiac function in patients with severe HF who are refractory to conventional therapy.

METHODS AND RESULTS

IA therapy was conducted in 16 patients with DCM (age 53 ± 4, male 8, New York Heart Association functional class III/IV, mean ejection fraction 18 ± 2%). Study subjects had autoantibodies directed against either β1-adrenergic or M2-muscarinic receptors. Plasma brain natriuretic peptide levels were significantly decreased after IA (P = 0.016). Plasma inflammatory cytokines including interleukin-6 and tumor necrosis factor-α did not change after each session of IA. Six-minute walk distance was significantly increased after IA (P = 0.01). Left ventricular ejection fraction increased by 3% 3 months after IA (P = 0.039).

CONCLUSIONS

Our initial experience demonstrated safety and short-term efficacy of IA using a new IgG3-specific tryptophan column for patients with advanced HF due to DCM. Long-term follow-up is needed to confirm the effects on cardiac function and morbidity/mortality in such patients.

Complete elimination of cardiodepressant IgG3 autoantibodies by immunoadsorption in patients with severe heart failure

BACKGROUND

Cardiodepressant IgG3 autoantibodies (CD-Abs) can be targeted by apheresis. Using blinded measurements of CD-Abs before and after immunoadsorption (IA), the cardiac function of patients who did or did not achieve complete CD-Abs elimination was compared.

METHODS AND RESULTS

Autoantibodies were completely removed from 18 patients with heart failure (New York Heart Association class 3 or 4, left ventricular ejection fraction (LVEF) <30%) using a selective IgG3 adsorption column. All patients had anti-beta1-adrenergic and/or M2-muscarinic autoantibodies before IA, and all LVEF were measured on radionuclide ventriculography. CD-Abs were measured before and after IA, and patient status was blinded until all measurements were collected. Treatment was defined as complete when CD-Abs status changed from positive to negative after IA. Other instances were defined as incomplete. Six-min walk test results and brain natriuretic peptide levels improved significantly after IA (P<0.01). The increase in LVEF 3 months after IA was significantly greater after complete treatment in comparison to the incomplete treatment group (19+/-8-29+/-9% vs 18+/-9-17+/-8%, P<0.01). Cardiac insufficiency events were also more frequent in the incomplete treatment group.

CONCLUSIONS

Complete elimination of CD-Abs with apheresis may be related to improved cardiac function in the treatment of heart failure.

The Treg/Th17 imbalance in patients with idiopathic dilated cardiomyopathy

To assess whether Treg/Th17 balance was broken in patients with idiopathic dilated cardiomyopathy (DCM). We studied 25 patients who were diagnosed as idiopathic DCM (18 men and seven women, mean age 35.6 +/- 5.2) and 25 normal persons (18 men and seven women, mean age 33.8 +/- 4.9). Then, we detected Treg/Th17 functions on different levels including cell frequencies, related cytokine secretion and key transcription factors in patients with idiopathic DCM and controls. The results demonstrated that patients with idiopathic DCM revealed significant increase in peripheral Th17 number, Th17-related cytokines (IL-17, IL-6, IL-23) and transcription factor (RORgammat) levels and obvious decrease in Treg number, Treg-related cytokines (TGF-beta1 and IL-10) and transcription factor (Foxp3) levels when compared to normal persons. Results indicated that Treg/Th17 functional imbalance existed in patients with idiopathic DCM, suggesting a potential role for Treg/Th17 imbalance in the development of idiopathic DCM.

Plasma exchange for removal of antibeta1-adrenergic receptor antibody in a small child with dilated cardiomyopathy

A 5-year-old boy was diagnosed with dilated cardiomyopathy (DCM) at 8 months of age. He underwent plasma exchange (PE) three times during 4 days because his antibeta1-adrenergic receptor antibody titer was 160 times the background density on enzyme-linked immunosorbent assay. BNP titer decreased from 1320 pg/ml before to 506 pg/ml after PE. Dobutamine infusion was discontinued after PE because of improving cardiac function. After PE, his antibeta1-adrenergic receptor antibody titer was < 20 times the background density. When patients have a high titer of antibeta1-adrenergic receptor antibody, PE should be considered, even in small children, as an alternative treatment.