Acute idiopathic pericarditis: current immunological theories Alida LP Caforio,1 Renzo Marcolongo,2 Antonio Brucato,3 Luca Cantarini,4 Massimo Imazio,5 Sabino Iliceto11Division of Cardiology, Department of Cardiology, Thoracic and Vascular Sciences, University of Padua, Padua; 2Haematology and Clinical Immunology, Department of Medicine, University of Padua, Padua, 3Internal Medicine, Ospedali Riuniti, Bergamo, 4Rheumatology Unit, Policlinico Le Scotte, University of Siena, Siena, 5Department of Cardiology, Maria Vittoria Hospital, Torino, ItalyAbstract: Idiopathic recurrent acute pericarditis (IRAP) is a rare disease of suspected immune-mediated pathogenesis. It represents a diagnosis of exclusion. It is necessary to rule out infectious and noninfectious causes of pericardial inflammation, including systemic autoimmune and immune-related disorders, eg, Sjögren’s disease, systemic lupus erythematosus. Since pericarditis may precede diagnosis of these disorders, IRAP diagnosis is often made after a long follow-up. According to the two main pathogenetic theories IRAP may represent an organ-specific autoimmune disease or an autoinflammatory disease (AInfD). The main evidence for autoimmunity in IRAP is provided by the detection of serum antiheart and antiintercalated-disk autoantibodies, and the response to anti-inflammatory or immunosuppressive therapy. The findings of familial forms and of proinflammatory cytokines in the pericardial fluid in IRAP would be in keeping with both organ-specific autoimmune disease and AInfD. In fact, AInfD are genetic disorders characterized by primary dysfunction of the innate immune system, due to mutations of genes involved in the regulation of the inflammatory response, in the absence of antigen specific T cells or autoantibodies. In AInfD there are active disease phases with raised non-cardiac specific inflammatory markers, such as C-reactive protein, as well as symptom-free intervals with possible C-reactive protein normalization. A minority of IRAP patients (6%) carry a mutation in the TNFRSF1A gene, encoding the receptor for tumor necrosis factor-alfa. This suggests that some IRAP patients may have an atypical or subclinical form of AInfD. Thus, IRAP may represent a syndrome with distinct pathogenetic mechanisms in different patients’ subsets.Keywords: pericarditis, autoimmunity, autoantibodies, heart disease, immune factors