Alteration of host defense mechanisms by murine cytomegalovirus infection.

An animal model of a sublethal infection, utilizing murine cytomegalovirus (MCMV), was developed to determine whether immunological factors could contribute to the establishment of a persistent viral infection. Adult female C3H mice inoculated intraperitoneally with 10(5) plaque-forming units of MCMV developed splenomegaly 5 to 12 days after infection. Virus replicated to peak titers (10(3) to 10(6) plaque-forming units per g of tissue) in liver, spleen, lung, kidney, and salivary gland tissue during the acute phase of the infection (3 to 12 days); it then decreased to undetectable levels in all tissues except salivary gland. Serum interferon was detected as early as 12 h after infection, peaked at 36 h (1,093 U/ml), and was undetectable by 4 days after infection. MCMV-infected animals were hyporeactive to interferon induction with New castle disease virus on days 5 to 9 of the infection. Splenic lymphocyte reactivity to phytohemagglutinin and lipopolysaccharide was normal early during the course of the infection, was suppressed during the acute phase of the infection, and had returned to normal by day 18. These data indicate that several parameters of host defense are transiently suppressed during the course of a MCMV infection. The capacity of cytomegaloviruses to alter host resistance may be one factor that contributes to the establishment of a persistent infection.