NRG1 and viral myocarditis: Immunohistochemistry demonstrated that Nup98, Nrg1 and erbB4 were all upregulated at 7 dpi and downregulated at 40 dpi, a time point of heart recovery from acute infection; however, at this time point their expression levels were still higher than that of the sham infected hearts (Figures 6D,E), indicating the strong immunoreactivity of proteins in the Nup98-Nrg1-erbB4 signaling axis during acute viral myocarditis in vivo.