SUMMARYMacrophages harvested from the peritoneal cavities of mice of several strains were permissive to infection with murine cytomegalovirus (MCMV). Macrophages from six mouse strains released equivalent amounts of plaque-forming virus into the culture fluids and cells from three mouse strains scored similarly in numbers of infectious centres. Twenty to 5o% of the infected macrophages obtained after thioglycollate activation formed infectious centres. When studied by in situ hybridization, more than 82% of infected macrophages (with or without thioglycollate activation) contained MCMV DNA.Macrophages obtained from latently infected mice were examined for their content of MCMV. Using co-cultivation assays, MCMV was frequently recovered from thioglycollate activated macrophages harvested from latently infected mice but only rarely recovered from non-activated macrophages. MCMV DNA-mouse DNA hybridization assays revealed four to seven virus genome DNA copies per ioo cells. These studies indicate that macrophages harvested from mice susceptible (BALB/cSt) or resistant (C3H) to MCMV infection replicated virus equivalently and that macrophages are a reservoir of MCMV during latent and chronic infections. Activation of macrophages may be one of the important steps leading to the exacerbation of in vivo latent infections.
One of the most challenging problems in medicine concerns latent virus infections, in particular the specific identification of tissues that harbor these viruses, the ways viruses persist, and the mechanism(s) by which such agents are activated . Cytomegalovirus (CMV),' like other herpes viruses, can persist within an organism in a latent form despite the presence of a vigorous antiviral immune response (reviewed in references 1 and 2) . Several epidemiologic surveys show that 40-80% of humans over the age of 40 have serologic evidence of prior CMV infection (1-3) and less than 1% of seropositive healthy individuals shed virus into their urine (4) . CMV infection would be regarded as an ordinary acute infection associated with numerous subclinical attacks, complete recovery, and eradication of the virus except that reappearance of this virus is common . For example, pregnancy is often associated with active CMV infection (5), and this virus has been recovered from up to 28% of pregnant women (6, 7) . Acute CMV infection occurs in nearly 90% of patients 1-2 mo after surgery for kidney transplantation (8) . CMV has been implicated as the cause of a mononucleosis-like illness occurring in patients after open heart surgery, and available evidence suggests that this infection is apparently transmitted by blood transfusions (9-13) . Both terminal leukemia and Hodgkin's disease in patients undergoing immunotherapy may also be associated with CMV infection (14) . The frequent occurrence of CMV infection in patients undergoing pregnancy, renal transplantation, and blood transfusions suggests that this virus may be activated by means of immunologic reaction to foreign antigens .Host-specific CMVs have been demonstrated in several species including guinea pig, rat, hamster, mouse, and man. The primary CMV infection in mice (MCMV) is very similar to that in man (15)(16) . Using the murine model, we studied whether MCMV was carried in lymphocytes taken from adult mice * This is publication no . 898
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.