Cell death, proliferation and repair in human myocarditis responding to immunosuppressive therapy

In this study, we evaluate cell death, proliferation and repair in left ventricular endomyocardial biopsies from 20 patients with active lymphocytic myocarditis worsening or recovering from cardiac dysfunction after 6-months immunosuppression. Apoptosis and necrosis were assessed by in situ ligation of hairpin probes, proliferation by Ki67 and MCM5 labelling of myocytes, repair by electron microscopy, morphometric study of percent myofibrillar area and real-time polymerase chain reaction of alpha-and beta-Myosin Heavy Chain (MHC). Apoptosis and necrosis decreased in post- vs pretreatment biopsies by 85 and 62%, respectively in responders, while increased by 42 and 46% in nonresponders. Ki67 and MCM5-positive myocytes were higher vs controls at baseline and increased by 43 and 38% at follow-up in responders and by 75 and 63% in nonresponders. Myofibrillar area reduced in pretreatment samples, increased by 33% at follow-up in responders, correlated with percent enhancement of ejection fraction and was associated with increased alpha-MHC expression and alpha/beta-MHC ratio. In follow-up biopsies of nonresponders, myofibrillar area diminished by 36% and correlated with percent decrease of ejection fraction. Our results suggest that recovery of cardiac function in myocarditis responding to immunosuppression is associated with inhibition of cell death, activation of cell proliferation and with newly synthesized contractile material.