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Atrial fibrillation (AF) is the most common sustained arrhythmia and carries an increased risk of stroke and heart failure. Here we investigated how the immune infiltrate of human epicardial adipose tissue (EAT), which directly overlies the myocardium, contributes to AF. Flow cytometry analysis revealed an enrichment of tissue-resident memory T (T RM ) cells in patients with AF. Cellular indexing of transcriptomes and epitopes by sequencing (CITE-seq) and single-cell T cell receptor (TCR) sequencing identified two transcriptionally distinct CD8 + T RM cells that are modulated in AF. Spatial transcriptomic analysis of EAT and atrial tissue identified the border region between the tissues to be a region of intense inflammatory and fibrotic activity, and the addition of T RM populations to atrial cardiomyocytes demonstrated their ability to differentially alter calcium flux as well as activate inflammatory and apoptotic signaling pathways. This study identified EAT as a reservoir of T RM cells that can directly modulate vulnerability to cardiac arrhythmia., (© 2024. The Author(s).)

Objective: To identify potential key biomarkers and characterize immune infiltration in atrial tissue of patients with atrial fibrillation (AF) through bioinformatics analysis., Methods: Differentially expressed genes (DEGs) were identified by the LIMMA package in Bioconductor, and functional and pathway enrichment analyses were undertaken using GO and KEGG. The LASSO logistic regression and BORUTA algorithm were employed to screen for potential novel key markers of AF from all DEGs. Gene set variation analysis was also performed. Single-sample gene set enrichment analysis was employed to quantify the infiltration levels for each immune cell type, and the correlation between hub genes and infiltrating immune cells was analyzed., Results: A total of 52 DEGs were identified, including of 26 downregulated DEGs and 26 upregulated DEGs. DEGs were primarily enriched in the Major Histocompatibility Complex class II protein complex, glucose homeostasis, protein tetramerization, regulation of synapse organization, cytokine activity, heart morphogenesis, and blood circulation. Three downregulated genes and three upregulated genes were screened by LASSO logistic regression and the BORUTA algorithm. Finally, immune infiltration analysis indicated that the atrial tissue of AF patients contained significant infiltration of APC_co_inhibition, Mast_cell, neutrophils, pDCs, T_cell_costimulation, and Th1_cells compared with paired sinus rhythm (SR) atrial tissue, and the three downregulated genes were negatively correlated with the six kinds of immune cells mentioned above., Conclusion: The hub genes identified in this study and the differences in immune infiltration of atrial tissue observed between AF and SR tissue might help to characterize the occurrence and progression of AF., Competing Interests: The authors declare that they have no conflicts of interest., (Copyright © 2022 Jie Liu et al.)

Sepsis is a known risk factor for new-onset atrial fibrillation (AF), and previous studies have demonstrated that ferroptosis participates in sepsis-induced organ injury development. Nevertheless, the role of ferroptosis in new-onset AF with sepsis remains largely unknown. This study aims to investigate the underlying mechanisms linking ferroptosis and AF caused by sepsis. LPS-induced endotoxemia is often used to model the acute inflammatory response associated with sepsis. Herein, we reported that ferroptosis was significantly activated in LPS-induced endotoxemia rat model. We also observed that ferroportin (Fpn), the only identified mammalian non-heme iron exporter, was downregulated in the atrium of endotoxemia model. Vulnerability to AF was also significantly increased in a endotoxemia rat model. Additionally, Fpn knockdown by shFpn further increased intracellular iron concentration and oxidative stress and exaggerated the AF vulnerability, which was alleviated by ferroptosis inhibition. Mechanistically, silencing Fpn worsened the alterations in calcium handling proteins expression in a endotoxemia rat model. These findings suggest that Fpn-mediated ferroptosis is involved in the new-onset AF with LPS-induced endotoxemia via worsening the calcium handling proteins dysregulation and provides a novel and promising strategy for preventing AF development in sepsis., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Exercise training is generally beneficial for cardiovascular health, improving stroke volume, cardiac output, and aerobic capacity. Despite these benefits, some evidence indicates that endurance training may increase the risk of atrial fibrillation (AF), particularly in highly trained individuals. Among multiple mechanisms, autonomic tone changes and atrial remodeling have been proposed as main contributors for exercise-induced AF. However, the contribution of local and systemic immunity is poorly understood in the development of atrial arrhythmogenic substrates. Here we aim to update the field of immunomodulation in the context of exercise and AF by compiling and reconciling the most recent evidence from preclinical and human studies and rationalize the applicability of "lone" AF terminology in athletes., Competing Interests: Declaration of Competing Interest None., (Copyright © 2021. Published by Elsevier Inc.)

Telocytes are interstitial cells with long, thin processes by which they contact each other and form a network in the interstitium. Myocardial remodeling of adult patients with different forms of atrial fibrillation (AF) occurs with an increase in fibrosis, age-related isolated atrial amyloidosis (IAA), cardiomyocyte hypertrophy and myolysis. This study aimed to determine the ultrastructural and immunohistochemical features of cardiac telocytes in patients with AF and AF + IAA. IAA associated with accumulation of atrial natriuretic factor was detected in 4.3-25% biopsies of left (LAA) and 21.7-41.7% of right (RAA) atrial appendage myocardium. Telocytes were identified at ultrastructural level more often in AF + IAA, than in AF group and correlated with AF duration and mitral valve regurgitation. Telocytes had ultrastructural signs of synthetic, proliferative, and phagocytic activity. Telocytes corresponded to CD117 + , vimentin + , CD34 + , CD44 + , CD68 + , CD16 + , S100 - , CD105 - immunophenotype. No significant differences in telocytes morphology and immunophenotype were found in patients with various forms of AF. CD68-positive cells were detected more often in AF + IAA than AF group. We assume that in aged AF + IAA patients remodeling of atrial myocardium provoked transformation of telocytes into "transitional forms" combining the morphological and immunohistochemical features with signs of fibroblast-, histiocyte- and endotheliocyte-like cells.

Despite our expanding knowledge about the mechanism underlying atrial fibrillation (AF), the interplay between the biological events underlying AF remains incompletely understood. This study aimed to identify the functionally enriched gene-sets in AF and capture their interconnection via pivotal factors, that may drive or be driven by AF. Global abundance of the proteins in the left atrium of AF patients compared to control patients (n = 3/group), and the functionally enriched biological processes in AF were determined by mass-spectrometry and gene set enrichment analysis, respectively. The data were validated in an independent cohort (n = 19-20/group). In AF, the gene-sets of innate immune system, metabolic process, cellular component disassembly and ion homeostasis were up-regulated, while the gene-set of ciliogenesis was down-regulated. The innate immune system was over-represented by neutrophil degranulation, the components of which were extensively shared by other gene-sets altered in AF. In the independent cohort, an activated form of neutrophils was more present in the left atrium of AF patients with the increased gene expression of neutrophil granules. MYH10, required for ciliogenesis, was decreased in the atrial fibroblasts of AF patients. We report the increased neutrophil degranulation appears to play a pivotal role, and affects multiple biological processes altered in AF.

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia in clinical practice and is known to be associated with significant morbidity and mortality. Previous studies suggested a link between inflammation and AF by findings of increased inflammatory markers in AF patients. However, it has not been finally clarified whether inflammation is a systemic or a local phenomenon reflecting an active inflammatory process in the heart. To address this subject, human left atrial appendage tissues were obtained from 10 patients who underwent cardiac surgery and subjected to immunohistochemical analysis. The number of inflammatory CD3-positive T cells significantly increased from patients with sinus rhythm to paroxysmal AF and persistent AF, respectively. Interestingly, in patients with persistent AF, these cells were frequently arranged in small clusters. Subsequently, the number of inflammatory CD3-positive T cells decreased and was significantly lower in patients with permanent AF than in patients with persistent AF. Inflammatory CD20-positive B cells could only be detected very occasionally in all AF subgroups and were not locatable in patients with SR. Hence, our data emphasize the potential prominent role of the cellular component of the immune system in the development and perpetuation of AF.

Sarcoplasmic/endoplasmic reticulum Ca 2+ adenosine triphosphatase (SERCA)2a, a critical regulator of calcium homeostasis, is known to be decreased in heart failure. Patients with myocarditis or dilated cardiomyopathy develop autoantibodies to SERCA2a suggesting that they may have pathogenetic significance. In this report, we describe epitope mapping analysis of SERCA2a in A/J mice that leads us to make five observations: 1) SERCA2a contains multiple T cell epitopes that induce varying degrees of myocarditis. One epitope, SERCA2a 971-990, induces widespread atrial inflammation without affecting noncardiac tissues; the cardiac abnormalities could be noninvasively captured by echocardiography, electrocardiography, and magnetic resonance microscopy imaging. 2) SERCA2a 971-990-induced disease was associated with the induction of CD4 T cell responses and the epitope preferentially binds MHC class II/IA k rather than IE k By creating IA k /and IE k /SERCA2a 971-990 dextramers, the T cell responses were determined by flow cytometry to be Ag specific. 3) SERCA2a 971-990-sensitized T cells produce both Th1 and Th17 cytokines. 4) Animals immunized with SERCA2a 971-990 showed Ag-specific Abs with enhanced production of IgG2a and IgG2b isotypes, suggesting that SERCA2a 971-990 can potentially act as a common epitope for both T cells and B cells. 5) Finally, SERCA2a 971-990-sensitized T cells were able to transfer disease to naive recipients. Together, these data indicate that SERCA2a is a critical autoantigen in the mediation of atrial inflammation in mice and that our model may be helpful to study the inflammatory events that underlie the development of conditions such as atrial fibrillation in humans., (Copyright © 2018 by The American Association of Immunologists, Inc.)

Background: Atrial fibrillation (AF) is the most common arrhythmia and despite obvious clinical importance remains its pathogenesis only partially explained. A relation between inflammation and AF has been suggested by findings of increased inflammatory markers in AF patients., Objective: The goal of this study was to characterize morphologically and functionally CD45-positive inflammatory cell populations in atrial myocardium of patients with AF as compared to sinus rhythm (SR)., Methods: We examined 46 subjects (19 with AF, and 27 in SR) undergoing coronary bypass or valve surgery. Peroperative bioptic samples of the left and the right atrial tissue were examined using immunohistochemistry., Results: The number of CD3+ T-lymphocytes and CD68-KP1+ cells were elevated in the left atrial myocardium of patients with AF compared to those in SR. Immune cell infiltration of LA was related to the rhythm, but not to age, body size, LA size, mitral regurgitation grade, type of surgery, systemic markers of inflammation or presence of diabetes or hypertension. Most of CD68-KP1+ cells corresponded to dendritic cell population based on their morphology and immunoreactivity for DC-SIGN. The numbers of mast cells and CD20+ B-lymphocytes did not differ between AF and SR patients. No foci of inflammation were detected in any sample., Conclusions: An immunohistochemical analysis of samples from patients undergoing open heart surgery showed moderate and site-specific increase of inflammatory cells in the atrial myocardium of patients with AF compared to those in SR, with prevailing population of monocyte-macrophage lineage. These cells and their cytokine products may play a role in atrial remodeling and AF persistence.

Activating autoantibodies to the β1-adrenergic and M2 muscarinic receptors are present in a very high percentage of patients with Graves' disease and atrial fibrillation (AF). The objective of this study was to develop a reproducible animal model and thereby to examine the impact of these endocrine-like autoantibodies alone and with thyroid hormone on induction of thyroid-associated atrial tachyarrhythmias. Five New Zealand white rabbits were coimmunized with peptides from the second extracellular loops of the β1-adrenergic and M2 muscarinic receptors to produce both sympathomimetic and parasympathomimetic antibodies. A catheter-based electrophysiological study was performed on anesthetized rabbits before and after immunization and subsequent treatment with thyroid hormone. Antibody expression facilitated the induction of sustained sinus, junctional and atrial tachycardias, but not AF. Addition of excessive thyroid hormone resulted in induced sustained AF in all animals. AF induction was blocked acutely by the neutralization of these antibodies with immunogenic peptides despite continued hyperthyroidism. The measured atrial effective refractory period as one parameter of AF propensity shortened significantly after immunization and was acutely reversed by peptide neutralization. No further decrease in the effective refractory period was observed after the addition of thyroid hormone, suggesting other cardiac effects of thyroid hormone may contribute to its role in AF induction. This study demonstrates autonomic autoantibodies and thyroid hormone potentiate the vulnerability of the heart to AF, which can be reversed by decoy peptide therapy. These data help fulfill Witebsky's postulates for an increased autoimmune/endocrine basis for Graves' hyperthyroidism and AF.

Using a micro-electrode technique we studied the effects of interleukin 1α and interleukin 1β on bio-electric activity of rat atrial myocardium under normal conditions and after gradual stretching. Perfusion with interleukin 1α increased the duration of the action potential at the level of 90% re-polarization. Stretch induced tachy-arrhythmia in the presence of interleukin 1α is mainly regulated via stretch increased nitric oxide production, while the ionotropic effect of the interleukin-1α during stretching is not pronounced. The perfusion with interleukin 1β did not change the values of the duration of the action potentials at the levels of 25, 50 and 90% repolarization. The interleukin lβ caused an appearance of extra-systolic patterns which turned into normal rhythm, alternating with periods of normal activity. The total intracellular nitric oxide level induced by both interleukin 1β and stretching is balanced by interleukin-1β induced cation influx., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Purpose of Review: Atrial fibrillation is the most common sustained arrhythmia, but its mechanisms are poorly understood. In particular, little is known about the factors that contribute to the establishment of persistent or permanent atrial fibrillation. This review addresses possible common signaling pathways that might promote both structural and electrical remodeling of the atria, thus contributing to atrial fibrillation perpetuation., Recent Findings: Sustained atrial fibrillation may trigger an inflammatory response leading to activation of myofibroblasts and to the release of cytokines such as transforming growth factor-β and platelet-derived growth factor, as well as profibrotic proteins such as galectin-3. Activation of signaling cascades involving such proteins is critical for the development of fibrosis and may also lead to ion channel dysfunction, which, along with myocyte apoptosis and extracellular matrix generation and turnover, likely contributes to both electrical and structural remodeling and predisposes to atrial fibrillation., Summary: Identifying upstream strategies targeting molecular pathways that are common to fibrosis and electrical remodeling leading to atrial fibrillation perpetuation is highly desirable. This would facilitate finding new target genes with pleiotropic effects on the expression of ion channel proteins in myocytes and profibrotic molecules in nonmyocyte cells that are important for pathologic remodeling, which could become an important goal in persistent atrial fibrillation therapy.

Alopecia areata (AA) is a chronic autoimmune hair loss disease that affects several million men, women and children worldwide. Previous studies have suggested a link between autoimmunity, stress hormones, and increased cardiovascular disease risk. In the current study, histology, immunohistology, quantitative PCR (qPCR) and ELISAs were used to assess heart health in the C3H/HeJ mouse model for AA and heart tissue response to adrenocorticotropic hormone (ACTH) exposure. Mice with AA exhibited both atrial and ventricular hypertrophy, and increased collagen deposition compared to normal-haired littermates. QPCR revealed significant increases in Il18 (4.6-fold), IL18 receptor-1 (Il18r1; 2.8-fold) and IL18 binding protein (Il18bp; 5.2-fold) in AA hearts. Time course studies revealed a trend towards decreased Il18 in acute AA compared to controls while Il18r1, Il18bp and Casp1 showed similar trends to those of chronic AA affected mice. Immunohistochemistry showed localization of IL18 in chronic AA mouse atria. ELISA indicated cardiac troponin-I (cTnI) was elevated in the serum and significantly increased in AA heart tissue. Cultures of heart atria revealed differential gene expression between AA and control mice in response to ACTH. ACTH treatment induced significant increase in cTnI release into the culture medium in a dose-dependent manner for both AA and control mice. In conclusion, murine AA is associated with structural, biochemical, and gene expression changes consistent with cardiac hypertrophy in response to ACTH exposure.

Background: A recent clinical study of patients with inappropriate sinus tachycardia reported that autoantibodies to β-adrenergic receptors (β2ARs) could act as agonists to induce atrial arrhythmias., Objective: To test the hypothesis that activating autoantibodies to the β2AR in the rabbit atrium are arrhythmogenic., Methods: Five New Zealand white rabbits were immunized with a β2AR second extracellular loop peptide to raise β2AR antibody titers. A catheter-based electrophysiologic study was performed on anesthetized rabbits before and after immunization. Arrhythmia occurrence was determined in response to burst pacing before and after the infusion of acetylcholine in incremental concentrations of 10 μM, 100 μM, and 1 mM at 1 mL/min., Results: In the preimmune studies when β2AR antibody titers were undetectable, of a total of 20 events, only 3 episodes of nonsustained (<10 seconds) atrial arrhythmias were induced. In the postimmune studies when β2AR antibody titers ranged from 1:160,000 to 1:1.28 million, burst pacing induced 10 episodes of nonsustained or sustained (≥10 seconds) arrhythmias in 20 events (P = .04 vs preimmune; χ(2) and Fisher exact test). Taking into account only the sustained arrhythmias, there were 6 episodes in 20 events in the postimmune studies compared with 0 episodes in 20 events in the preimmune studies (P = .02). Immunized rabbits demonstrated immunoglobulin G deposition in the atria, and their sera induced significant activation of β2AR in transfected cells in vitro compared to the preimmune sera., Conclusions: Enhanced autoantibody activation of β2AR in the rabbit atrium leads to atrial arrhythmias mainly in the form of sustained atrial tachycardia., (Published by Elsevier Inc.)

Background: Fish oil (FO) has antiinflammatory effects, which might reduce systemic inflammation induced by a cardiopulmonary bypass (CPB)., Objective: We tested whether perioperative infusions of FO modify the cell membrane composition, inflammatory responses, and clinical course of patients undergoing elective coronary artery bypass surgery., Design: A prospective randomized controlled trial was conducted in cardiac surgery patients who received 3 infusions of 0.2 g/kg FO emulsion or saline (control) 12 and 2 h before and immediately after surgery. Blood samples (7 time points) and an atrial biopsy (during surgery) were obtained to assess the membrane incorporation of PUFAs. Hemodynamic data, catecholamine requirements, and core temperatures were recorded at 10-min intervals; blood triglycerides, nonesterified fatty acids, glucose, lactate, inflammatory cytokines, and carboxyhemoglobin concentrations were measured at selected time points., Results: Twenty-eight patients, with a mean ± SD age of 65.5 ± 9.9 y, were enrolled with no baseline differences between groups. Significant increases in platelet EPA (+0.86%; P = 0.0001) and DHA (+0.87%; P = 0.019) were observed after FO consumption compared with at baseline. Atrial tissue EPA concentrations were higher after FO than after control treatments (+0.5%; P < 0.0001). FO did not significantly alter core temperature but decreased the postoperative rise in IL-6 (P = 0.018). Plasma triglycerides increased transiently after each FO infusion. Plasma concentrations of glucose, lactate, and blood carboxyhemoglobin were lower in the FO than in the control group on the day after surgery. Arrhythmia incidence was low with no significant difference between groups. No adverse effect of FO was detected., Conclusions: Perioperative FO infusions significantly increased PUFA concentrations in platelet and atrial tissue membranes within 12 h of the first FO administration and decreased biological and clinical signs of inflammation. These results suggest that perioperative FO may be beneficial in elective cardiac surgery with CPB.

Deficiency of the programmed cell death-1 (PD-1) gene enhances T-cell activation and increases inflammation levels. It has been reported that atrial fibrillation (AF) is closely related to inflammation. The aim of the present study was to investigate the role of PD-1 deficiency in the pathogenesis of AF. Two groups of mice were used in our experiment: the C57BL/6 and the C57BL/6-PD-(1-/-) group. The expression of the inflammatory cytokines interleukin (IL)-2, -4, -6, -10, -17, interferon-γ and tumor necrosis factor were detected. Furthermore, the levels of atrial myocyte oxidative stress, the atrial effective refractory period (AERP) and the atrial myocardial fibrosis levels were determined. Compared with the C57BL/6 group, we found that the inflammatory cytokines were significantly increased in the PD-1(-/-) group and the levels of atrial myocyte oxidative stress in the PD-1(-/-) group were also higher. The AERP became shorter and the dispersion of AERP was increased in the PD-1(-/-) group. Moreover, the PD-1(-/-) group presented significant atrial myocardial fibrosis but the C57BL/6 group did not. Our findings strongly suggest that the higher levels of inflammatory cytokines and atrial myocyte oxidative stress were present in the PD-1(-/-) mice and resulted in atrial electricity and structural remodeling. Due to the atrial remodeling, the PD-1(-/-) mice were more likely to develop AF.

To investigate the effects of age and disease on endogenous cardiac progenitor cells, we obtained right atrial and left ventricular epicardial biopsies from patients (n = 22) with chronic ischaemic heart disease and measured doubling time and surface marker expression in explant- and cardiosphere-derived cells (EDCs, CDCs). EDCs could be expanded from all atrial biopsy samples, but sufficient cells for cardiosphere culture were obtained from only 8 of 22 ventricular biopsies. EDCs from both atrium and ventricle contained a higher proportion of c-kit+ cells than CDCs, which contained few such cells. There was wide variation in expression of CD90 (atrial CDCs 5-92 % CD90+; ventricular CDCs 11-89 % CD90+), with atrial CDCs cultured from diabetic patients (n = 4) containing 1.6-fold more CD90+ cells than those from non-diabetic patients (n = 18). No effect of age or other co-morbidities was detected. Thus, CDCs from atrial biopsies may vary in their therapeutic potential.

Background: The presence of serum autoantibodies against β(1) adrenoreceptors (β(1)-ARs) in human gingival fibroblast from patients with periodontitis inhibits primary cell-specific growth and induces over-expression of pro-inflammatory mediators. Serum β(1)-AR autoantibodies from patients with periodontitis react with myocardium and modify cardiac contractility. The relationship between the presence of serum β(1)-AR autoantibodies and alterations in heart rate variability (HRV) was also studied., Methods: An enzyme-linked immunosorbent assay (ELISA) using cardiac and gingival fibroblast membranes or synthetic peptides corresponding to the second extracellular loop of human β(1)-AR was used to detect serum autoantibodies. The HRV was assessed from RR interval files generated from 22:00 to 08:00 hours. The autoantibody effects on contractility were measured on spontaneous rat isolated atria., Results: Circulating autoantibodies from 36 patients with periodontitis and 20 healthy individuals (controls) interacted with fibroblasts, the cardiac surface, and β(1)-AR synthetic peptides. The distributions of serum antibodies against gingival and myocardium membranes and β(1)-AR synthetic peptide were 88.8%, 77.7%, and 92.8%, respectively. Moreover, 88.5% of patients with periodontitis whose sera were positive against β(1)-AR synthetic peptide had decreased HRV. The corresponding affinity-purified anti-β(1)-AR peptide IgG displayed partial agonist-like activity modifying the isolated atria contractility., Conclusion: This manuscript describes that patients with periodontitis showed increased levels of serum IgG with reactive activity against β(1)-AR. Those patients demonstrated decrease in heart rate, and IgG derived from their sera induced aberrant contractility of heart atrium. We propose that periodontitis increases the risk of cardiovascular diseases, although it increases anti-β(1)-AR autoantibody that alters myocardial contractility., (© 2011 John Wiley & Sons A/S.)

Background: Epicardial ganglionated plexi (GP) ablation can prevent atrial fibrillation inducibility. However, the long-term effects of GP ablation on atrial fibrillation have not been elucidated., Methods: Thirteen adult dogs of either sex, weighing 13-17kg, were randomly assigned to a sham-operated group (n=6) or a GP ablation group (n=7). After right thoracotomy, the atrial effective refractory period (AERP) was measured and atrial fibrillation was induced by right atrial rapid burst pacing. Atrial fibrillation and AERP were remeasured after anterior right and inferior right GP ablation in the GP ablation group. The animals were allowed to recover for 8 weeks, after which atrial fibrillation and AERP were measured again. Concentrations of C-reactive protein, tumour necrosis factor-alpha (TNF-α) and interleukin-6 were measured in the blood and atrial tissues., Results: After 8 weeks, atrial fibrillation was induced in all animals in the GP ablation group. AERP and dispersion of AERP (dAERP; maximum AERP minus minimum AERP) were increased after GP ablation but AERP recovered after 8 weeks. There were no significant differences in the concentrations of C-reactive protein, TNF-α or interleukin-6 in venous blood between the two groups and the concentration of C-reactive protein in the atrium did not change before and after GP ablation. However, the concentrations of TNF-α and interleukin-6 in the atrium increased significantly 8 weeks after GP ablation (P<0.05)., Conclusion: Increased concentrations of TNF-α and interleukin-6 in the atrium after GP ablation provide a new causative factor in terms of atrial fibrillation vulnerability., (Copyright © 2011 Elsevier Masson SAS. All rights reserved.)

Background: Atrial fibrillation has been associated with increased oxidative stress, elevated inflammatory status and endothelial dysfunction. However, the underlying mechanisms regulating the expression of inflammatory markers or oxidative stress status are unclear. We searched for clinical determinants of oxidative stress status, endothelial function and inflammatory process in patients with chronic atrial fibrillation., Methods: Sixty nine patients with chronic atrial fibrillation at a stable clinical state were recruited. Ejection fraction of the left ventricle and the dimensions of the left atrium were determined echocardiographically. Flow mediated dilatation (FMD) was evaluated in the brachial artery, while serum oxidized LDL (ox-LDL), matrix metalloproteinase-9 (MMP-9), soluble CD40-ligand (sCD40L) and C-reactive protein (CRP) were measured., Results: FMD was correlated with CRP (r=-0.423, p=0.028), independently of other clinical parameters (beta(SE): -0.0039(0.00159), p=0.022). Ox-LDL was significantly correlated with left atrium diameter(r=0.358, p=0.005) independently of other clinical variables (beta(SE):1.288(0.455), p=0.007). The only independent predictors of MMP-9 were sCD40L (beta(SE):17.232(7.654), p=0.028), CRP (beta(SE):4.249(2.186), p=0.05) and gender (beta(SE):204.657(68.153), p=0.004), but not left atrium dimensions. Independent predictors of CRP were hypertension (beta(SE): 8.531(3.973), p=0.036), sCD40L (beta(SE): 0.779(0.408), p=0.06) and age (beta(SE): 0.381(0.201), p=0.063)., Conclusions: There is a strong link between inflammation and endothelial function, in patients with atrial fibrillation. The maximum diameter of left atrium is the only independent predictor of oxidized LDL, suggesting that left atrium distension may predict oxidative stress status in these patients.

Background: Inflammatory processes in the atria during systemic inflammation remain unclear, so this study tested the hypothesis that macrophages infiltrate the atrial myocardium mainly through the atrial endocardium with the contribution of fractalkine., Methods and Results: Sprague-Dawley rats were injected with lipopolysaccharide (LPS) to simulate inflammation in the atria. Inflammation was immunohistologically assessed by the presence of macrophages. Macrophage infiltration was diffuse throughout the atrial myocardium after LPS injection. At an earlier phase after LPS injection, the number of macrophages dramatically increased, mainly in the atrial endocardium, and the expression of fractalkine protein was markedly increased by treatment with LPS in the atrial endocardium. The LPS-induced increase in atrial macrophage infiltration was significantly suppressed by neutralizing the fractalkine protein (P<0.01)., Conclusions: In an experimental model of atrial inflammation, macrophages infiltrated the myocardium mainly through the atrial endocardium with the contribution of fractalkine. Inhibition of macrophage infiltration by suppressing chemokine expression could be a novel therapeutic approach to controling acute inflammation in the atria.

Background: Evidence has shown that autoantibodies against M2 muscarinic acetylcholine receptors may play a role in the development of atrial fibrillation. The goal of this study was to evaluate the effects of anti-M2 receptor autoantibodies on rabbit atria in vivo., Methods: Rabbits were immunized monthly with a synthetic peptide corresponding to the M2 receptor. The atrial electrophysiology of the isolated perfused rabbit hearts was studied. Western blots and RT-PCR were performed to determine the expression of the atrial muscarinic receptor and the acetylcholine-activated potassium channel. Atrial tissue was stained with Masson's trichrome stain for fibrosis detection., Results: Autoantibodies were persistently detected in immunized rabbits. M2 rabbits showed a significantly shorter atrial effective refractory period and a longer intra-atrial activation time than control rabbits. Electrical stimuli induced a significantly larger number of repetitive atrial responses in M2 rabbits. The protein levels of the M2 receptor and GIRK4 were upregulated in M2 rabbits. The mRNA levels of GIRK1 and GIRK4 were also upregulated. Histological examination revealed significantly increased diffuse fibrotic deposition in M2 rabbit atria compared with control rabbits., Conclusion: The M2 receptor autoantibody-positive rabbits showed altered atrial electrophysiology, overexpression of the M2 receptor-I(K,ACh) pathway and atrial fibrosis, which indicates that the autoantibodies against M2 receptors may participate in the induction and perpetuation of atrial fibrillation., (Copyright 2008 S. Karger AG, Basel.)

Objectives: To depict the interaction between atrial fibrillation (AF) and inflammatory reaction, studies were taken to measure the activity of NF-kappaB in myocardium, the concentration of regional inflammatory factors and the pathological process of the right atrium in patients with AF., Design: Patients with valvular disease with AF or sinus rhythm (SR) were recruited and compared. Before the extracorporal circulation, about 250 mg tissue of right atrium was collected for pathological examination. The activity of NF-kappaB in myocardium was measured by electrophoretic mobility shift assay (EMSA), and the concentration of cardiac tissue interleukin-6 (IL-6) and tumor necrosis factor (TNF-alpha) was determined by radioimmuoassay., Results: Patients with valvular disease with AF exhibited higher NF-kappaB activity, higher concentration of TNF-alpha and IL-6, severe lymphomonocyte infiltration, and more fibrosis than those patients with valvular disease with SR. There were significant positive correlations among NF-kappaB activity and levels of TNF-alpha and IL-6 and collagen volume fraction., Conclusions: This study proved the presence of inflammation in atrial myocardium by triggering inflammatory reaction.

Background: Atrial fibrillation is the most common complication after cardiac surgery. Postoperative atrial fibrillation (PAF) has been shown to increase length of stay, morbidity, and mortality. Because the clinical behavior of PAF parallels that of inflammation following surgery, we investigated the effect of the inflammatory mediator arachidonic acid on the electrical behavior of normal atrial tissue in vitro and assessed the efficacy of the topical application of anti-inflammatory drugs at suppressing PAF in an animal model., Methods: To study changes in electrical behavior from inflammation, the conduction properties of six normal canine right atrial appendages were quantified as a function of the direction of impulse propagation with and without 80 mum arachidonic acid. To study the effect of topical anti-inflammatory drugs, 24 adult mongrel dogs were prepared according to the model of sterile talc pericarditis. Nine dogs received talc alone (T), seven received talc combined with 600 mg ibuprofen (T + I), and eight received talc combined with 10 mg methylprednisolone (T + M). Three days following preparation, programmed electrical stimulation was performed to quantify conduction characteristics and to attempt the induction of atrial fibrillation (AF)., Results: In vitro, arachidonic acid produced an anisotropic and rapidly reversible 36.1 +/- 3.4% (P = 0.01) decrease in conduction velocity transverse to the long axis only. In vivo, both ibuprofen and methylprednisolone significantly reduced the incidence of sustained AF (from 56 to 0% T + I and 12% T + M, respectively, P = 0.02). No differences in conduction velocities or refractory periods were seen during sinus rhythm among the groups., Conclusions: Acute inflammation as mimicked by arachidonic acid slows conduction anisotropically, mainly transverse to the long axis of the atrial myocardial fibers. This may set the stage for reentry. Preventing inflammation in vivo by the topical application of anti-inflammatory drugs supports this hypothesis, suggesting a possible role for inflammation in the genesis of postoperative atrial fibrillation and shedding light on the mechanism underlying PAF.

Recent evidence suggests that inflammatory cytokines, particularly tumor necrosis factor alpha (TNF-alpha), may play a role in heart disease. Elevated plasma levels of the cytokine have been reported in congestive heart failure and severe angina and after myocardial infarction. The exact role of TNF-alpha in heart disease and how production is stimulated and regulated in the heart are current areas of investigation. Regarding regulation of production, isoproterenol elevates cyclic AMP and inhibits TNF-alpha release in macrophages. Therefore we hypothesized that stimulation of beta-adrenergic receptors of the sympathetic nervous system would inhibit release of the cytokine from heart tissue. With Institutional Review Board approval and patient consent atrial tissue was obtained during preparation for cardiac bypass. The tissue was divided into segments, placed in culture medium, and incubated for various times in the presence or absence of lipopolysaccharide (LPS) (20 microg/mL) and/or isoproterenol (1 microM). The medium was removed and analyzed for biologically active TNF-alpha by the L929 cell cytotoxicity assay. Tissue samples were weighed and TNF-alpha release was expressed as pg TNF-alpha/mg tissue. Initially, to determine the time course of release, measurements were made at 2, 5, 10, 15, 30, 60, 120, 180, and 360 minutes after the addition of LPS. Elevated TNF-alpha levels in the culture medium were reliably detected at 360 minutes after exposure to LPS. In atrial tissue obtained from seven patients TNF-alpha released into the culture medium at 360 minutes was 6 +/- 3 pg/mg tissue. In the presence of LPS, levels of the cytokine in the culture medium increased to 604 +/- 233 pg/mg tissue (P < 0.05 vs LPS alone). When isoproterenol and LPS were simultaneously added to the culture medium release of TNF-alpha was reduced by 87 per cent to 82 +/- 40 pg/mg tissue (P < 0.05 vs LPS alone). Our results show that activation of the beta-adrenergic receptor inhibits myocardial production of TNF-alpha. This finding suggests that the sympathetic nervous system inhibits production of the cytokine and that impaired sympathetic function in heart failure may play a role in the elevated levels of TNF-alpha.

Recent data suggest that auricular thrombosis is associated with an increase and accumulation of mast cells (MC) in the subendothelial region of the upper endocardium. However, the molecular basis and the functional role of MC in this process are not known. In the current study, expression of fibrinolytic and antifibrinolytic antigens in human cardiac MC was analyzed by immunohistochemistry. MC were found to react with antibodies against tissue-type plasminogen activator (tPA) and urokinase receptor (uPAR/CD87), but not with antibodies against urokinase (uPA) or plasminogen activator inhibitors (PAI-1, PAI-2). Significant changes were observed when the phenotype of accumulated MC in the upper endocardium in patients with auricular thrombosis was compared with the phenotype of myocardial MC in the same patients or with MC in normal hearts. These redistributed MC stained less intensely with antibodies against tPA and chymase but retained their staining for tryptase and uPAR. Together, these data indicate that cardiac MC are a source of fibrinolytic antigens and that accumulation of MC in auricular thrombosis is associated with phenotypic changes of MC and loss of cellular tPA. It is hypothesized that MC and their products may play a role in endogenous fibrinolysis in auricular thrombosis.

Macrophages are important in inflammatory processes in heart disease and in transplantation rejection. A resurgence of interest in the macrophage has emanated from recent evidence implicating it as an effector cell in atherosclerosis and transplantation rejection. The detailed distribution of the macrophage within the normal human heart is unknown. We quantified macrophage numbers in the different chambers of the heart. Large tissue blocks (1.5-2.0 cm3) were removed from specific sites in 5 'normal' control hearts (2 males, 3 females, age range 19-46 y). Paraffin-embedded sections were stained with a CD68 pan macrophage marker. Positive cells were enumerated within 20 random fields. Results were analysed using a generalised linear modelling method using the Poisson distribution. Macrophages were identified within septa, and often close to blood vessels, in the myocardium, and in the majority of areas in all hearts. Macrophage numbers varied significantly between areas (range 0-6 cells/high power field; P < 0.001), and between the 5 hearts analysed (P < 0.001). In general, there were significantly more macrophages in the ventricles (RV P < 0.01, LV P < 0.05), but these differences were affected by heart differences. This study provides a baseline for the range of macrophage numbers within normal hearts, thus enabling comparisons with macrophage numbers within diseased and transplanted hearts.

Expression and distribution of atrial natriuretic peptide (ANP) were studied immunohistochemically in the conducting system and internodal atrial myocardium of 5 adult human hearts. Myocytes from the sinus node and compact atrioventricular node were usually ANP-negative; only a very few cells exhibited ANP immunoreactivity. These ANP-positive myocytes were small and did not appear to be trapped working atrial myocytes which are larger than nodal cells. The transitional cell zones of the sinus node and the atrioventricular node were composed of bundles of ANP-positive myocytes, intermingled with non-reactive myocytes. The internodal atrial myocardium exhibited a comparable intensity of myocyte staining in each case examined. Thus, morphologically distinct connecting pathways between the sinus node and the atrioventricular node with regard to myocyte ANP immunoreactivity could not be demonstrated, reinforcing the notion that they actually do not exist. The penetrating bundle, branching bundle and bundle branches were usually composed of ANP-negative myocytes although some ANP-positive myocytes were observed in the branching bundle and bundle branches in 4 cases. Myocytes from the ventricular conducting tissue presenting ANP immunoreactivity have been designated Purkinje fibers and have been found in several mammalian species.

Tumour necrosis factor (TNF), a cytokine produced mainly by macrophages, has also been found in vascular smooth muscle cells. Elevated serum levels of TNF have been reported in various cardiac diseases, especially congestive heart failure (CHF). Although the myocardium produces several cytokines, the expression of TNF in human cardiac tissue has not yet been demonstrated. We examined TNF expression in right atrial (RA) specimens obtained from 15 patients during cardiac surgery with immunohistochemistry using an anti-human TNF monoclonal antibody, enzyme-linked immunosorbent assay (ELISA) and reverse transcriptase polymerase chain reaction (RT-PCR). TNF immunoreactivity was found only in cardiac myocytes and some vascular smooth muscle cells of small vessels of specimens from patients with severe CHF (3/5), and not in those from patients without severe CHF (0/10). ELISA of four RA specimens revealed that RA tissues from two patients with severe CHF contained more TNF than did those from two patients without severe CHF (3.1 and 4.7 pg/mg vs. 0.1 and 0.3 pg/mg). RT-PCR revealed TNF mRNA in all seven cases we examined. It was concluded that TNF mRNA is expressed by atrial tissue. The production of immunoreactive TNF-like peptides by myocytes and vascular smooth muscle cells is augmented in patients with severe CHF.

The interaction of the IgG from Trypanosoma cruzi-infected mice (chagasic IgG) with cardiac cholinergic receptors by means of specific radioligand binding and by production of cholinergic-mediated cellular transmembrane signals was characterized. Chagasic IgG inhibited, in a noncompetitive manner, the binding of [3H]quinuclidinyl benzilate to the cardiac membrane. Moreover, chagasic IgG could modify all of the muscarinic cholinergic effects mediated by a G regulatory protein, i.e., decrement of atria contractility, inhibition of cAMP, or activation of the turnover of phosphoinositides via phospholipase C. The cGMP production was also increased by the antibody. The data demonstrated that chagasic IgG interacting with cardiac muscarinic cholinergic receptor triggers the biological effects associated with cholinergic-mediated cellular transmembrane signals. The implications of the results in the pathogenesis of Chagas' myocarditis are discussed.

The rejection of a transplanted heart leads to an accumulation of mononuclear cells in the cardiac tissue and to reactions of the antigen-recognizing cells with the foreign tissue. Consequently, during rejections immunologic changes, such as the number of mononuclear cells and the patterns of mononuclear cell subpopulations, should be detectable by analysis of mononuclear cells from the coronary sinus of transplanted hearts. Seventy-nine endomyocardial biopsies were performed in 37 patients. Severity of graft rejection was classified by the Billingham scheme. Thirty-two biopsy specimens showed no rejection, 33 mild, and 14 moderate rejection. After endomyocardial biopsy the coronary sinus was catheterized under x-ray guidance. Heparinized blood samples were obtained from the coronary sinus and the right atrium, and mononuclear cell counts and subpopulation pattern were compared. Patients without rejection and patients with mild rejection showed no significant differences in the patterns of mononuclear cell subpopulation identified in right atrium blood. However, a significant (1.56-fold) increase of mononuclear cells was assessed in the CS blood (p less than 0.01). Moderate rejections showed a 4.2-fold augmentation of mononuclear cells in the coronary sinus (p less than 0.005) compared with nonrejections. In addition, the T-helper/inducer (CD4) percentage increased from 27.1% in the right atrium to 41.2% in the coronary sinus (p less than 0.005), natural killer cells (CD16) from 17.7% to 31.8% (p less than 0.005), and the interleukin 2 receptor-bearing cells from 6.6% to 15.3% (p less than 0.005). Percentage of pan-T cells (CD3), T-cytotoxic/suppressor cells (CD8), and monocytes (CD14) showed no statistically significant changes. These findings correlated with grading according to endomyocardial biopsy. Using the ratio of values obtained from cells of the coronary sinus and the right atrium rendered the coronary sinus immunologic monitoring independent of changes in the administered immunosuppressive regimen. The specificity of the described method was as good as that of endomyocardial biopsy. It is concluded that the discrimination of the patterns of mononuclear cell subpopulations from right atrium versus coronary sinus blood samples is highly sensitive and allows the correct diagnosis of graft rejection within 1 to 2 hours.

Antilaminin IgG was bound to cholinergic muscarinic receptors of normal mice heart and released TXB2, simulating the biological effect of a cholinergic agonist. Antilaminin IgG interfered with the binding of the radiolabelled muscarinis antagonist (-)3H-QNB in a noncompetitive fashion. Following the interaction of the antibody with the cholinergic receptor, an increased production of TXB2 occurred. This effect required the activation of the muscarinic cholinergic system, because it was blunted by atropine and mimicked by acetylcholine.

Endothelin-like immunoreactivity (-LI) was present in the guinea-pig cardiopulmonary tissues with the associated autonomic neural supply. The highest levels were found in the stellate ganglion (15 pmol g-1) followed by the vagus nerve, pulmonary artery, lung and right atrium of the guinea-pig. Endothelin I, but not endothelin III, induced an increase in contractile force and frequency followed by an atropine-resistant inhibition of right atrial contractility at higher concentrations. Exposure to endothelin I caused a pronounced, long-lasting coronary vasoconstriction as revealed by a decrease in perfusate outflow. In addition, both heart and contractile force were attenuated. Guinea-pig bronchi in vitro contracted upon exposure to endothelin I and III, but only endothelin I caused contraction of pulmonary arteries. The C-terminal hexapeptide of endothelin I did not influence right atrial, bronchial or pulmonary artery contractility. Endothelin I increased the mean arterial pressure and insufflation pressure and decreased the heart rate in the guinea-pig in vivo. In conclusion, endothelin-LI is present in the cardiovascular, respiratory and nervous tissues of the guinea-pig and endothelin induces strong coronary and pulmonary vasoconstrictor effects. The effects on atrial contractile force and frequency are concentration-dependent with stimulation at lower and inhibition at higher concentrations. Based on the diversity in response to endothelin III in the bronchi compared to atrium and pulmonary artery, it may be suggested that different receptor populations exist in bronchial and cardiovascular muscle, although the cellular localization and forms of endothelin present in guinea-pig cardiopulmonary tissue remain to be established.

It has been previously demonstrated that murine alloimmune lymphoid cells were able to exert positive or negative inotropic effects on isolated mouse atria depending on the cellular type used. Here we show that BALB/c anti-C3H B-cells induced positive inotropic action on C3H mouse atria. Supernatants of alloimmunized B-cells co-cultivated with C3H myocardium exerted the same biological effect as alloimmune B-cells, indicating that a soluble factor is involved. Inhibitors of lipoxygenase(s) of arachidonic acid metabolism and a SRS-A blocker inhibited the positive effect of immune cells or its supernatants. The effect was prevented when we inhibited the atria lipoxygenase activity. On the other hand, when the inhibitors were applied to effector cells the response was not modified. In addition, supernatants of B-cells cultured with alloextracts were inactive. Supernatants from alloimmune B-cells plus myocardium release higher amounts of LTC4 than those from normal B-cells. It is proposed that SRS-A synthesis is induced in the atria by direct contact with alloimmune B-cells upon recognition of alloantigens expressed by atria cells; which in turn, triggers the positive inotropic effect.

Purified IgG from murine alloimmune sera directed against class I products from the major histocompatibility complex of the mouse, could bind to the beta-adrenoceptors and stimulate contractile activity of myocardium. Immune IgG inhibited the binding of (-) 3H-DHA to beta-adrenoceptors of mouse myocardial membranes behaving as a competitive inhibitor. Moreover, immune IgG induced positive inotropic and chronotropic effects on isolated mouse atria. These effects could be blocked by beta-adrenoceptors antagonists. Data prove that immune IgG directed against specific alloantigens are able to recognize the beta-adrenoceptors and mimic the stimulation of the beta-adrenoceptor agonist.

Hybridomas were prepared from mice immunized with myosin from the enlarged left ventricle of a 53-year-old female with an obstructive cardiomyopathy. The specificity of 15 monoclonal antibodies to myosin heavy chains was assessed by the reactivity of muscle extracts and of chymotryptic myosin fragments of different sizes with these antibodies, as determined by the immune replicate technique; some of the monoclonal antibodies cross-reacted only with the ventricular V3-type myosin from hypothyroid rats, whereas the other antibodies cross-reacted both with the latter and with the ventricular V1-type myosins from normal young rats. Immunological heterogeneity of the fibers from human atrial muscles and from human ventricular muscles was detected by some of the antimyosin antibodies by means of indirect immunofluorescence. Histochemical fiber heterogeneity was also detected by adenosine triphosphatase staining of the same tissues. Because of the close correspondence observed between the immunological and histochemical responses of atrial fibers, it has been postulated that at least two distinct types of myosin exist in the human atrium, each myosin form being histochemically related to either alpha- or beta-like ventricular myosin heavy chains. In contrast, there was no direct correspondence between the two experimental approaches in human ventricles, and it is postulated that at least three distinct types of myosin exist within the human ventricles, one V1-type myosin, presumably corresponding to the very rare fibers with an alkaline-stable adenosine triphosphatase activity, and two other V3-type myosins corresponding to immunologically different fibers, each having an alkaline-labile adenosine triphosphatase activity. Monoclonal antibodies that can distinguish among the different myosin variants were further used to provide the basis for an anatomical description of fiber types and myosin types within the human atrial and ventricular myocardium in the whole hearts of two young boys who died sudden violent deaths. Small zones of myosin variation were seen to be scattered, but probably not randomly distributed, within large areas of myocardium in which the cellular distribution of myosin was constant; the large areas had one myosin distribution specific for each cardiac cavity. No clear-cut conclusions can yet be made concerning the physiological role of the regional variations observed in the distribution of the different molecular forms of myosin.

The myocardiu m of a young patient who had clinically established cardiomyopathy and suspected Coxsackie virus B4 infection was studied. Coxsackie B4 viral antigen was found in the ventricular and atrial myocardium by specific immunofluorescent antibody staining. Histologic examination revealed varying degrees of myocardial damage. Interstitial fibrosis and edema, swelling and deterioration of hypertrophic muscle fibers, connective tissue proliferation, stasis of small coronary blood vessels, atrophy of myocardial fibers with pyknosis of nuclei, and lytic deterioration were observed. Electron microscopic examination showed portions of the Z bands to be either widened or displaced into the sarcomere. Adjacent cell membranes in the region of the intercalated disc in the myocardium of both the ventricle and the atrium were separated, forming large gaps. Morphologic changes were most pronounced in the atrium adjacent to the mitral valve, in which the mitochondria were grossly swollen, and large vesicles were present in the sarcoplasm. The pathologic changes found in the myocardium of all chambers of the heart apparently were due to Coxsackie B4 viral infection.

Induction of polyphosphoinositide hydrolysis in cardiac tissue by specific recognition of class I histocompatibility antigens was assayed. C3H (H-2k) mice auricles were labelled with myo-[3H]inositol precursor and inositol phosphate production in the presence or absence of anti-class I k products was measured. Anti-class I, but not anti-class II products specifically increased phosphoinositide turnover. This increment was partially blocked by muscarinic cholinergic and alpha-adrenergic blockers and even more so by the phospholipase C inhibitor NCDC. Alloantibodies specifically directed against class I antigens could then exert stimulation of phospholipase C-mediated phosphoinositide hydrolysis through the interaction with muscarinic cholinergic and/or alpha-adrenergic receptors. The induction of intracellular second messengers by class I antigens and hormone-receptor interactions is discussed.

Alloimmunized lymphoid cells exert inotropic effects on isolated mouse atria. We here show that, when thymocytes were assayed on spontaneously beating isolated atria, a negative inotropic effect always appeared. When lymph node or spleen cells were assayed, they led to a biphasic effect: negative or positive inotropic effect, depending on the number of immunizations. Non-immunized lymphoid cells never exerted inotropic effects. Supernatants of alloimmunized cells cocultivated with pieces of atria from the immunizing strain exerted pharmacological effects on atria that mimicked those of whole cells. Inhibitors of lipoxygenase(s) and cyclooxygenase of arachidonic acid metabolism, inhibited the positive and negative inotropic effects, respectively. The specificity of the negative and positive inotropic effects, both in their induction and expression, was linked to the major histocompatibility complex. When T and B cells were purified from lymphoid tissues we found that they were responsible for the negative and positive inotropic effects on atria, respectively. Additionally, supernatants of T cells cultured with alloextracts triggered negative inotropic effects, but those from B cells were inactivated.

Immunologic histamine release was evoked from the sensitized fragmented cardiac and pulmonary tissue of the cynomolgus monkey by a reverse anaphylactic reaction. Ventricular and pulmonary tissue released a similar fraction (approximately 6%) of the total tissue histamine when challenged with antihuman IgE, presumably reflecting the 'active' sensitization of the monkey in vivo. Passive sensitization of these tissues in vitro resulted in significantly greater immunologic histamine release in 6 of the 14 ventricles and d a similar fraction (approximately 6%) of the total tissue histamine when challenged with antihuman IgE, presumably reflecting the 'active' sensitization of the monkey in vivo. Passive sensitization of these tissues in vitro resulted in significantly greater immunologic histamine release in 6 of the 14 ventricles and d a similar fraction (approximately 6%) of the total tissue histamine when challenged with antihuman IgE, presumably reflecting the 'active' sensitization of the monkey in vivo. Passive sensitization of these tissues in vitro resulted in significantly greater immunologic histamine release in 6 of the 14 ventricles and in the lungs. The antiallergic compounds, disodium cromoglycate and SK&F 64398, inhibited immunologic histamine release from passively sensitized monkey ventricular tissue. These results demonstrate that ventricular histamine may be immunologically released and that this release process can be pharmacologically inhibited in a manner similar to that of pulmonary tissue.

An antibody reacting with the plasma membrane of working myocardial cells, skeletal muscle fibres, and endothelial cells (EVI antibody) has been described in the sera of patients with Chagas' disease. In the present study of rat isolated atrial preparations beating in ddifferent media, direct immunofluorescence and ultrastructural immunohistochemical procedures indicate that the antibody can interact with the living tissue, becoming fixed to the plasma membranes. Transmission electronmicroscopy studies also showed the presence of sarcolemmal alterations. These observations suggest a possible pathogenic effect of the EVI antibody. The presence of EVI-positive sera in the beating medium leads to a significant increase in the frequency of contractions; no significant effects of EVI-positive sera in contractile force were seen. The increase in frequency could be prevented by previous treatment with a b-adrenergic blocking agent (MJ-1999), but not by an x-blocker (phentolamine) or by an anti-histamine compound (cyproheptadine). The changes described were observed only in those atrial preparations which were beating in media containing EVI-positive sera. In those atria beating in control media (KR,KR plus normal human serum, KR plus EVI-negative chagasic serum), neither immunological nor morphological or functional changes wersence of EVI-positive chagasic serum diminished atrial stimulation after added norepinephrine. These results suggest the possibility that the EVI antibody may act as a b-adrenergic agonist at the cell plasma membrane level. Such an effect might account for some of the clinical features of chronic Chagas' heart disease.