Springer Semin Immunopathol (1989) 11:409-422 Springer Seminars in Immunopathology © Springer-Verlag 1989 Humoral Immune Response to Cardiac Conducting Tissue Ulrich Lotze 1 and Bernhard Maisch 2 1 University Hospital of Internal Medicine, Department of Internal Medicine III, University of Saarland, D-6650 Homburg/Saar, Federal Republic of Germany 2 Department of Internal Medicine-Cardiology, Philipps-University Marburg, Baldinger Strasse, D-3550 Marburg, Federal Republic of Germany Introduction Wherease autoimmune reactivity is well established in thyroid and other endocrine diseases, in muscular, dermatological and connective tissue diseases [13], only very few investigations have been carried out on humoral immune reactions in cardiac conducting and automaticity disturbances. There are few reports concern- ing the etiology and contributing pathogenetic factors compared to the wealth of literature on the electrophysiology or pharmacotherapy of conduction disorders. This contribution summarizes data from the literature and our own investiga- tions on the immune response to cardiac conducting tissue [6, 7, 18, 21, 25, 29, 38-41, 44, 51, 56, 61, 62]. The Sick Sinus Syndrome (SSS) Clinical and Etiological Features The SSS was first described by Lown [31] and Ferrer [19]. Clinical features are palpitations, angina pectoris, heart failure, dizziness and also, but rarely, systemic emboli. The diagnosis is based on clinical symptoms, conventional ECG or 24 h-Holter monitoring. The SSS presents electrocardiographically with different manifestations, e. g., the sinuatrial (SA) block, the tachycardia-bradycardia syn- drome and the pathological sinusbradycardia [9, 19, 20]. In histopathological studies [15] the sinuatrial disorders were attributed to disproportional ageing of the sinus node and the atrial muscle: according to Davies and coworkers [15] sinus node and atrial tissue possess a higher content of collagen and have lost nodal cells. Idiopathic fibrosis of the sinus node, mostly described as age-related [15], deposits of amyloid staining material [47] or replacement of the sinus node tissue by fat [27] was also observed. Even lymphocytic infiltration Offprint requests to: U. Lotze