Idiopathic dilated cardiomyopathy: lack of association between circulating organ‐specific cardiac antibodies and HLA‐DR antigens

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Abstract
Organ‐specific cardiac antibodies are serological markers of autoimmunity in dilated cardiomyopathy (DCM). HLA‐DR4 and possibly DR5 are immunogenetic markers of susceptibility in DCM, but it is not known whether they are associated with autoantibody production. We studied the frequency of HLA‐DR antigens and the presence of organ‐specific cardiac antibodies in 80 DCM Caucasian patients from Northern Italy. HLA‐DR typing was performed by serology; 289 healthy blood donors from the same region were tested as controls. HLA‐DR frequencies in DCM were also compared with VIII International Workshop control data for Italy. Cardiac antibodies were detected by indirect immunofluorescence on human heart. Skeletal muscle was used to identify cross‐reacting antibodies. The prevalence of cardiac antibodies in DCM was: organ‐specific 34% and skeletal muscle cross‐reactive 30%. The previously reported positive association between DCM and HLA‐DR4 was confirmed using either the controls from the same region (21.25% vs 10.73% p = 0.02, relative risk = 2.30) or from all of Italy (21.25% vs 12.3%, p = O.O3). HLA‐DR5 frequency was slightly but not significantly higher in DCM than in controls from the same region (46.25% vs 31.49% p = 0.02, relative risk of 1.87, p corrected = NS) or from all of Italy (46.25% vs 35.8% p = NS). HLA‐DR3 frequency was lower in DCM than in controls from the same region (12.50% vs 29.41% p = 0.003, relative risk of 0.36, p corrected = 0.03). This negative association was not confirmed using the control data from the whole of Italy (12.50% vs 16.5% p = NS). No significant association was found between HLA‐DR4, DR5 and/or DR3 and cardiac antibody status, age, sex, symptom duration. The lack of association between HLA‐DR and the presence of cardiac antibodies may be due to disease heterogeneity and/or reduction of antibody levels with disease progression, which are well‐recognised features of organ‐specific autoimmune conditions.