Biology of mouse thymic virus, a herpesvirus of mice, and the antigenic relationship to mouse cytomegalovirus.
Mouse thymic virus (TA) is a herpesvirus which produces extensive necrosis of the thymus of newborn mice 7 to 14 days after infection. Infectious virus can be recovered from the thymus for only 10 days after infection, with highest titers occurring between days 5 and 7. In mice 5 days old or less, TA infects thymus cells and produces massive necrosis. TA also infects the salivary glands and persists as a chronic infection. Newborn mice infected with TA have no detectable humoral immune response. Infected adult mice respond, and humoral antibody is detected 7 days after infection. Titers are maintained for months thereafter. Regardless of the age of the mice inoculated with TA, persistent infection was established in the salivary glands, but no evidence for thymus involvement was observed when adults were infected. TA does not cross-react serologically by immunofluorescent, complement fixation, or virus neutralization tests with mouse cytomegalovirus; however, interestingly, the epidemiology of the two herpesviruses are similar. Both mouse cytomegalovirus and TA were isolated from the same animals in populations of laboratory and wild mice. Evidence of infection with mouse cytomegalovirus and TA were most apparent by virus isolations, since humoral antibody responses are rarely observed. All strains of mice tested were susceptible to TA infection. However, in some strains maximum necrosis occurred at 7 days, compared with 10 to 14 days for other strains. The difference in age susceptibility and the target tissue of thymus in newborn mice suggests that TA is a model herpesvirus for studying the effects of viral infections on humoral and cell-mediated immunological functions.