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Human herpesvirus-6 (HHV-6) exhibits a predominant tropism for CD4+ T-lymphocytes, but can infect other components of the blood as well as surrounding tissue and organs. To understand the role of the endothelium in the transmission and haematogenous spread of this virus, human umbilical vein endothelial cells (HUVEC) were infected with HHV-6 and monitored for viral gene expression. The presence of both early and late viral antigens was demonstrated by indirect immunofluorescence in 37.6 and 6.5%, respectively, of HUVEC. However, attempts to detect the release of infectious virus were not successful, indicating infection is semipermissive in nature. Upon continued passage of infected HUVEC monolayers, HHV-6 antigen-positive cells persisted up to 27 days post-infection. Furthermore, the virus could be recovered from HUVEC monolayers that contained fewer than 1% antigen-positive cells by co-cultivation with peripheral blood mononuclear cells. Together, these findings suggest that endothelial cells may serve as a reservoir for harbouring HHV-6.

To study the roles of beta 2-microglobulin (beta 2-m) and major histocompatibility complex (MHC) class I expression in human cytomegalovirus (HCMV) infection, the ability of HCMV strain AD-169 to infect and replicate in a human melanoma cell line (FO-1), which is beta 2-m-deficient and cannot express MHC class I on its cell surface, was examined. Susceptibility of FO-1 cells was compared with human foreskin fibroblasts (HFF) and FO-1H cells (FO-1 cells that have been transfected with the human beta 2-m gene, restoring MHC I expression on the cell surface). As judged by the HCMV immediate early 1 (IE-1) antigen expression, HCMV was able to infect FO-1 cells, although somewhat less efficiently than HFF. However, the expression of HCMV late (L) antigen and the production of virus was significantly less for FO-1 cells than for HFF. Analysis of the FO-1H transfectants revealed that expression of IE-1 and L HCMV antigens was comparable to FO-1 cells, which lack MHC I. Treatment of FO-1 and FO-1H cells with sodium butyrate prior to inoculation did not alter the expression of MHC I in either cell type, but did increase susceptibility of both cell types to HCMV infection, as well as the expression of L antigens and production of virus. These studies indicate that HCMV infection of FO-1 cells is independent of beta 2-m and MHC class I expression.

We have developed a hybridoma, designated 25G11, which produced a monoclonal antibody (MAb) reactive with a 52K protein of murine cytomegalovirus (MCMV). This MAb, 25G11, was reactive with a protein band of 52K in MCMV-infected cell lysates and with a protein of 49K in human CMV (HCMV)-infected cell lysates as detected by immunoblot analysis. With purified MCMV virions, 25G11 gave a faintly immunoreactive band of 52K. However, no immunoreactive protein band was detected with purified HCMV virions, nor with purified HCMV or MCMV envelope preparations. By immunocytochemistry, 25G11 detected viral antigen primarily in the nucleus of HCMV- or MCMV-infected cells. The antibody 25G11 was used to screen a lambda gt11 library of HCMV DNA fragments. One of the isolated clones (lambda 32323B) was employed for gene mapping on the HCMV genome, which suggested that the immunoreactive HCMV protein was the DNA-binding protein (ICP36). Analysis of the recombinant fusion protein with antibody 25G11 and with an MAb (CH16) specific for an HCMV DNA-binding protein confirmed the identity of the cross-reacting protein as ICP36. Furthermore, we found that whereas the epitope recognized by 25G11 was conserved between HCMV and MCMV proteins, the epitope recognized by CH16 was unique to HCMV and thus represents a variable region in the protein.

We examined the role of T lymphocytes bearing the L3T4 phenotype in acute murine cytomegalovirus (MCMV) infection. In vivo administration of rat IgG2b monoclonal antibody (MAb) GK 1.5 was used to deplete mice of L3T4+ lymphocytes during acute MCMV infection. Unlike the saline-treated controls that resolved their infections, mice receiving the MAb developed persistent and high levels of virus in the salivary gland, lung and spleen. The production of antibody to MCMV was delayed and the titres achieved were markedly less than in the controls. Despite the higher levels of virus replication, there was no increase in mortality seen in animals treated with the MAb. Following intraperitoneal challenge with MCMV, depletion of L3T4+ lymphocytes was protective, increasing the dose of MCMV required to produce death. These data indicate that T lymphocytes of the L3T4 phenotype influence the degree of MCMV replication during acute infection and may contribute to mortality following intraperitoneal virus challenge.

When searched for by standard virological methods, murine cytomegalovirus (MCMV) becomes undetectable by 4 months after inoculation of mice. However, a 2-week regimen of immunosuppression with antilymphocyte serum and corticosteroid results in reactivation and dissemination of the virus in virtually all animals. This system should be useful in defining the pathogenesis of generalized cytomegalic disease resulting from reactivation of latent virus in immunocompromised individuals.

We evaluated the influence of host genetic factors on the course of murine cytomegalovirus (MCMV) lung infection after intranasal inoculation and on the development of interstitial pneumonitis after virus and cyclophosphamide (CP) administration. Susceptibility to virus replication in the lungs of various inbred murine strains was inherited as an autosomal dominant trait, which was associated with the H-2 locus. Similarly, the development of MCMV interstitial pneumonitis was inherited as an autosomal dominant, polygenic trait. Susceptibility to lung infection was necessary, but not sufficient for MCMV interstitial pneumonitis. Non-H-2-associated factors were also needed and probably related to CP metabolism or the character of immune recovery after CP administration. Therefore, inheritable host factors influence both susceptibility to MCMV lung infection and the genesis of MCMV interstitial pneumonitis.

Ultraviolet irradiation of murine cytomegalovirus (MCMV) caused a rapid dose-related decline in virus infectivity, manifested by virus antigen induction, and in virus production as measured by plaque formation and infectious centre assay. The virus survival curve was multi-component, suggesting host cell-assisted reactivation. Multiplicity reactivation and photoreactivation of MCMV were not observed in these experiments. Productive infection was more sensitive to u.v. irradiation than was virus antigen production, indicating differential inactivation of virus functions. The effects of u.v. irradiation were similar in most respects to those reported for human cytomegalovirus.