Characteristics of testicular lesions in mice infected with a low dose of encephalomyocarditis (EMC) virus.

We investigated the characteristics of testicular lesions induced in mice with a low dose (10 plaque forming units/mouse) of the D variant of encephalomyocarditis (EMC-D) virus. The virus titers of blood and testis peaked at 5 days post-inoculation (5 DPI) and were no longer detected at 14 DPI. The IFN-gamma and iNOS mRNAs expression in the testis and spleen detected by RT-PCR was prominently elevated at 7 DPI, although the expression level of TNF-alpha mRNA was not affected. Signals of viral RNA were clearly detected in degenerative germinal epithelia (in situ hybridization) at 7 DPI, which were surrounded by a small number of macrophages and a few CD4 + T cells and CD8 + T cells (immunohistochemistry). Signals were no longer detected at 21 DPI when seminiferous tubules were highly degenerative and accompanied with infiltration of many macrophages and a small numbers of CD4 + T cells and CD8 + T cells. At 35 DPI, marked atrophy of germinal epithelia composed of Sertoli cells alone was observed, and there were almost no infiltrating cells detected. The present results suggest that macrophages may play an important role in the development of testicular lesions induced in mice with a low dose of EMC-D.