Ken Kohno

Experimental autoimmune myocarditis and its pathomechanism.

The pathomechanisms of autoimmune myocarditis are quite different from viral infection. In this type of myocarditis, cardiac myosin fragments, proper dentritic cells and autoreactive T cells are the 3 major elements in initiating and promoting the inflammation. The causative epitope is locating on the S2 rod portion of the myosin heavy chain (MHC). Through our recombinant study, the peptide was found to be located on the latter half of MHC residues 1070 to 1165. Activity of antigenicity was not different between α and β chain. The cardiac dentritic cell presents a unique structure with large mononuclear and interdigitating process. This antigen presenter is quickly activated and suppressed by the antigen. The autoreactive T cell is closely linked with cytokine production. In the initial stage of myocarditis, IL-2 and IL-12 are increased. According to the progression of inflammatory changes, a great amount of IL-1b, INF-γ and TNF-α is released around the diseased tissue. At the same time, NO is massively produced from infiltrating macrophages. Cytokines secreted from inflammatory cells accelerate T cell induction from Th0 to Th1. In the convalescent stage, production of TGF-β1 and IL-10 become dominant. They contribute to cell induction from Th0 to Th2.ZusammenfassungDie Pathomechanismen einer Autoimmunmyokarditis unterscheiden sich von denen einer viralen Entzündung. Bei einer autoimmunen Myokarditis kommt kardialen Myosinfragmenten, dendritischen Zellen und autoreaktiven T-Zellen eine entscheidende Bedeutung für die Auslösung und das Fortestehen der Entzündung zu. Das auslösende Epitop befindet sich auf dem S2-Teil der schweren Kette von Myosin (MHC). Unsere rekombinanten Studien haben gezeigt, dass sich das Epitop auf der zweiten Hälfte der MHC-Aminosäuren 1070 bis 1165 befindet. Das Ausmaß der Antigenität der α- und β-Ketten war nicht verschieden. Die kardialen dendritischen Zellen haben eine charakteristische Morphologie mit großen mononukleären ineinander greifenden Fortsätzen. Diese Antigen präsentierende Zelle wird schnell durch das Antigen aktiviert und später supprimiert. Die autoreaktive T-Zelle ist entscheidend an der Zytokinproduktion beteiligt. Im initialen Stadium der Myokarditis sind die IL-2- und IL-12-Spiegel erhöht. Beim Fortbestehen der Entzündung werden große Mengen von IL-1b, INF-γ und TNF-α in der Randzone des entzündeten Gewebes und gleichzeitig NO durch infiltrierende Makrophagen freigesetzt. Die durch Entzündungsquellen freigesetzten Zytokine beschleunigen den T-Zell-Übergang von Th0 nach Th1. Im Ausheilungsstadium überwiegt die Produktion von TGF-β1 und IL-10 und führt zum Übergang von Th0- zu Th2-Lymphozyten.

A Peptide Fragment of β Cardiac Myosin Heavy Chain (β-CMHC) Can Provoke Autoimmune Myocarditis as well as the Corresponding a Cardiac Myosin Heavy Chain (α-CMHC) Fragment

The validity of the general belief that a cardiac myosin heavy chain (α-CMHC) is primarily responsible for causing experimental autoimmune myocarditis because of the more profound tolerance induction to β-CMHC due to its expression during the embryonic stage has been examined. In order to completely avoid cross-contamination among components of the two myosin heavy chains, recombinant myosin fragments were synthesized in Escherichia coli using cDNA fragments of rat a- and (J-CMHC cloned by reverse transcription polymerase chain reaction (RT-PCR). Two fragments corresponding to amino acid residues 1107-1164 derived from a-and β-heavy chains were equally capable of provoking severe myocarditis in Lewis rats when immunized in complete Freunďs adjuvant. No significant differences in the severity, as judged from histological scoring, were observed between the diseases induced by the two different peptide fragments, indicating conclusively that β-CMHC is as pathogenic as α-CMHC.

Myosin Autoreactive T Cells And Autoimmune Myocarditis. Lessons from the Disease Caused by Cardiac Myosin Peptide CM2

We have proposed a unique animal model of experimental autoimmune myocarditis (EAM). This rat myocarditis is systematically provoked by immunization with cardiac myosin, and evolves toward dilated cardiomyopathy through repetitive immunizations. In this process, myosin epitopes, dendritic cells and myosin autoreactive T cells are the three major elements initiating and promoting this disease. Despite many attempts, we have failed, thus far, to identify myosin autoreactive and myocarditogenic T cells in vitro. However, recently, T cell lines specifically reactive to the cardiac myosin peptide, CM 2 (AA: 1539-1555), and showing myocarditogenecity have been identified. Line characterization of harvested T cells from EAM rats rendered ill by whole cardiac myosin was repetitively and systematically tested. Thus, T cell lines autoreactive to CM 2 and inducing transfer myocarditis were isolated out of many candidates. Acute myocarditis transferred by means of these T cell lines became more severe, and disease transfer with these cell lines caused chronic myocarditis in syngenic Lewis rat. Importantly, the myosin autoreactive and myocarditogenic T cells were also able to transfer the myocarditis into SCID mice beyond the MHC restriction.

Fulminant Myocarditis—From Lethal Disease to Survival

Fulminant myocarditis is a representative lethal heart disease, in which patients have only been urgently rescued with the help of mechanical cardiopulmonary supports. Nevertheless, the therapeutic outcomes of fulminant myocarditis treated with PCPS has not been elucidated. Recently, a national survey was conducted to undertake these tasks by considering the current situation of patients in Japan and to propose a therapeutic guidelines for fulminant myocarditis using PCPS. Thirty (57.7%) out of 52 patients could be rescued in the survey. Important factors concerning the prognosis were the severity and improvement grade of cardiac and renal dysfunction. Based on the data, management guidelines using PCPS to improve the survival rate of fulminant myocarditis patients were published. Of the individual prognosis of patients treated with PCPS, limiting factors have not been identified even in the present survey.