INFECTION WITH RAT CYTOMEGALOVIRUS (CMV) IN THE IMMUNOCOMPROMISED HOST IS ASSOCIATED WITH THE APPEARANCE OF A T-CELL POPULATION WITH REDUCED CD8 AND T-CELL RECEPTOR (TCR) EXPRESSION

Infection with human cytomegalovirus (HCMV) mostly results in a chroni c subclinical infection; the immune system is unable to eliminate the virus and is apparently in equilibrium with the persistent virus. In t he immunosuppressed host this equilibrium is disturbed, resulting in c linical infection. Rat cytomegalovirus (RCMV) infection in its host ca n be used as a model for HCMV infection. Using flow cytometry we exami ned the effect of acute RCMV infection on the composition of leucocyte subsets in the peripheral blood of both immunocompetent and immunosup pressed (5 Gy total body irradiation) Lewis rats. Special attention wa s paid to the natural killer (NK) cells and the CD8(+) T cells known t o be involved in the control of viral infections. Furthermore, we dete rmined the presence of leucocyte subsets in the internal organs by imm unohistochemistry. In immunocompetent rats, infection caused a small i ncrease in NK cells and a large increase in CD8(+) T cells. In contras t, infection of immunosuppressed rats caused a marked increase in NK c ells and a small increase in CD8(+) T cells, consisting of T cells wit h reduced expression of both CD8 and TCR. This phenomenon is character istic of anergic CD8(+) T cells, possibly explaining the ability of th e virus to escape elimination by the immune system. The increase of NK cells in the peripheral blood of immunosuppressed, RCMV-infected rats could also be detected in kidney, liver, lung and pancreas, but not i n salivary gland. This could explain the long persistence of infectiou s Virus in the salivary gland.