Identification of cardiac myosin peptides capable of inducing autoimmune myocarditis in BALB/c mice.(1)
T-cell mediated myocarditis for an autoimmune heart disease can be induced by immunization with cardiac myosin. This study identified pathogenic epitopes on the myosin molecule.
There are two isoform of myosin: cardiac alpha myosin and soleus muscle beta myosin. The alpha myosin can induce severe carditis with high prevalence as an immunodominant isoform whereas beta myosin fails it. The fact provides the difference of amino acid sequences in the two isoforms may suggest the immunodominant epitopes.
Postviral myocarditis is a serious disorder, often resulting in dilated cardiomyopathy. As a virus-free system, a cardiac myosin immunization can induce myocarditis in mice. The model expresses the pathological mechanisms in postinfectious autoimmune heart disease.
The myosin was purified from 4 week-old young adult rats because alpha myosin exclusively exists in the young animals. The older animals increase the ratio of beta myosin contents age dependently.
Note: The rat alpha myosin could induce myocarditis in mice but mouse alpha myosin failed. How is the bovine alpha myosin which can be purified with high yield.
This study used 6-8 week- old Balb/cJ mice as a recipient of the immunization. They received two immunizations of 1 mg/ml peptide with complete Freund’s adjuvant (CFA) at a 7 days interval. At day 21, hearts were evaluated.
Note: The model requires heart histological studies. It may not be convenient for continual studies.
Mice and rats shared higher than 99% of amino acid sequence in myosin. Therefore rat alpha and beta myosin amino acid sequence were compared. Several regions show the difference of the sequence below.
The peptide of 614-643 received acetylation could induce myocarditis with higher incidence and severity. The peptide has 12 amino acids difference between alpha and beta myosin. However, the peptide must have the acetylation. Instead, the peptide 735-747 and 947-960 without the acetylation could induce mild myocarditis with lower incidence. These peptides have only one amino acid difference between alpha and beta myosin. The acetylation may be important to reveal the immunogenicity reported by Zhao et al (2).
Interestingly, the peptide of 1304-1320 could induce myocarditis in LEW rats, but it failed in Balb/c mice. It suggests that the MHC molecules in animals individually play roles for recognition of antigen to activate T-cells which induce myocarditis. For example, immunization of the peptide 334-352 can induce myocarditis in A/J mice who have I-Ak but not in Balb/c mice (I-Ad). Thus, selection of epitopes are very important to induce T-cell dependent disease models.
2. W. Zhao, K. W. Wegmann, J. L. Trotter, K. Ueno, W. F. Hickey, Identification of an N-terminally acetylated encephalitogenic epitope in myelin proteolipid apoprotein for the Lewis rat. J. Immunol. 153, 901–909 (1994).