The novel coronavirus SARS-CoV-2 has developed into a pandemic and led to millions of deaths. Because of its close relation to other coronaviruses which were earlier associated with acute myocarditis and its entrance via the ACE2 receptor which is located on the surface of cardiomyocytes it was assumed that SARS-CoV-2 has an impact on the heart. This relation allowed the prediction of potential antigens (Grifoni 2020) which lead to the activation of the immune system. Case reports of corona patients describe cardiac involvement with myocardial inflammation and high hsTnT levels. In some heart biopsies SARS-CoV-2 virus particles were found in the myocardium. It is unknown if the immune response induced by the SARS-CoV-2 infection could affect the myocardium and / or other organs (such as muscle, lung, liver or intestine) by induction of cross reactivity or epitope spreading. The findings of this research could contribute to a better understanding of the long-term side effects of infection with SARS-CoV-2 and its potential impact on other organs.
Methods
To study the effect of inducing an immune response to SARS-CoV-2 proteins we synthetized 38 most immunogenic epitopes to these proteins. These peptides were produced on the basis of Grifoni et al (2020) and include section of corona spike protein (SP), envelope protein (EP), membrane protein (MP) and nuclear capsid protein (NCP). 6 weeks old A/J mice were immunized i.p. with each corona peptide sequence (n=6 mice each group) three times over three weeks. Analysis of hsTnT level in mouse sera and histopathological staining were done. Enzyme linked Immuno Assay (ELISA) was used to investigate the immune reaction and associated antibody formation against the peptide sequences was induced.

Results
The evaluation of produced antibodies against the individual peptide sequences revealed titers with variously strong manifestations with mean values between those of the animals treated with SP02 (Ø=1:2.8e+006) and those treated with SP03 (Ø=1:2000) (Fig. 1). Neither histopathological examination nor measurement of hsTnT levels revealed inflammation of the heart (Ø=0). Other organs also showed no signs of inflammation as a result of treatment with single or pooled peptide sequences (Ø=0). Except for the intestine where the mean values of observed inflammation of the intestine of the SPG4 (Ø=2), SPG5 (Ø=2), NPG (Ø=2.33) and MPG (Ø=2.16) treated animals were higher than those of the untreated ones (Ø=1.67) (Fig. 2).

Fig.1: Logarithmic representation of the antibody titers of the mice against the spike proteins SP01-SP06 (A) and the antibody titers of the animals against the pooled peptide sequences of four spike protein sequences each (SPG1-SPG5) as well as the nuclear capsid peptides (NPG), the membrane peptides (MPG) or the envelope proteins (EPG) (B).

Fig.2: Level of Inflammation observed during histopathological examination of the HE-stained paraffin sections of the intestine.