Apoptotic changes in the thymus of mice infected with mouse hepatitis virus, MHV-2.

In mice infected with MHV-2, histopathological changes of the thymus was studied. Extensive cell lysis with pyknotic nuclear debris appeared at 48 hr postinfection, and cortico-medullary border was indistinguishable. Electron microscopy revealed vacuolation and shrinkage of the cytoplasm of lymphoid cells, margination of nuclear chromatin, and fragmentation of nuclei. Virus particles were detectable in the lymphoid and reticular epithelial cells, being immunohistochemically positive for viral antigen. By DNA electrophoresis thymocytes showed DNA fragmentation with a laddering pattern characteristic of apoptosis.