- Volume 77, Issue 2, 1996

Recombinant vaccinia viruses (VV) expressing the varicella-zoster virus (VZV) glycoprotein H (gH) or glycoprotein L (gL) were constructed. The 94 kDa gH intermediate glycoprotein was synthesized in cell cultures infected with the VV-gH recombinant, but only coinfection with both recombinants resulted in the synthesis of the fully processed 118 kDa gH molecule. The VV-expressed gH and gL formed a complex that displayed the conformational neutralization epitope detectable by means of human VZV gH-specific monoclonal antibody V3. Formation of this epitope was inhibited by tunicamycin but not by monensin. Simultaneous intraperitoneal inoculation of mice with high doses of both VV-gH and VV-gL viruses resulted in the development of VZV-neutralizing, complement-independent antibodies; these antibodies were not detected in mice infected solely with either the VV-gH or the VV-gL recombinant.

It has been claimed that MHC class I proteins serve as receptors for murine cytomegalovirus (MCMV) and that this interaction is the most important mechanism for virus entry in most cells. This claim is based on the observation that the MHC haplotype contributes to the susceptibility to cytomegalovirus (CMV) infection in vivo. Results from in vitro studies support the concept that stable expression of correctly folded MHC class I molecules contributes to infection, since the individual properties of MHC class I alleles, the availability of β 2-microglobulin (β 2m) and also the degree of peptide charging of the MHC class I heavy chain β 2m heterodimers determined the infection phenotype of cell lines. To assess the biological relevance of proper MHC class I expression we investigated CMV infection in β 2m-deficient mice which fail to express ternary MHC class I complexes and lack peripheral CD8+ T lymphocytes. We found that organ virus titres and virus clearance kinetics were not altered in β 2m mutant mice. In addition, there was no indication of diminished virus propagation in β 2m−/− embryonic fibroblasts. β 2m−/− mice suffered from the lack of CD8+ T lymphocytes that was partially compensated for by the function of CD4+ T lymphocytes. An organ-specific anti-virus function of natural killer (NK) cells was observed, independent from the β 2m deletion. The immune control unique for salivary gland infection was maintained. From the data presented here, we confirm the role of MHC class I molecules in the immune surveillance of CMV infection but question the biological impact of correct MHC class I complexes for productive infection.

To develop a transformation system with a conditional Epstein—Barr virus nuclear antigen 2 (EBNA2) gene, we fused the hormone binding domain of the oestrogen receptor to the N or C terminus of EBNA2. In promoter transactivation as well as primary B cell transformation assays these chimeric EBNA2 proteins are able to substitute for wild-type EBNA2 in the presence of oestrogen. Here we provide evidence that this transformation is the result of double infection of a cell with two virions, the P3HR1 virus genome and a mini-EBV plasmid carrying the chimeric EBNA2 gene. Unexpectedly, expression of the same EBNA2-oestrogen receptor fusion protein in established human B cell lymphoma lines resulted in growth retardation or growth arrest upon the addition of oestrogen. By titrating the oestrogen concentration in these stably transfected cells, the growth retarding and the transactivating function of the chimeric proteins could not be dissociated. We propose that growth inhibition of established B cell lymphoma lines is a novel function of EBNA2 which has not been detected in the absence of an inducible system. It remains open whether the growth retarding property of the EBNA2-oestrogen receptor fusion protein in B cell lymphoma lines is due to unphysiologically high expression of the chimeric protein or to interference with a cellular programme driving proliferation in these cell lines.