SummaryThe bcl-2 gene product has been shown to prevent apoptotic cell death. We have now investigated the bcl-2 protein expression by resting and activated mature T cell populations. Freshly isolated CD45RO + T cells within CD4 + and CD8 + subsets expressed significantly less bcl-2 than CD45RO-(CD45RA +) T cells ~ <0.001). When CD45RA + T cells within both CD4 ~ and CD8 + subsets were activated in vitro, the transition to CD45RO phenotype was associated with a decrease in bcl-2 expression. Patients with acute viral infections such as infectious mononucleosis caused by Epstein-Barr virus infections or chickenpox, resulting from variceUa zoster virus infection, had circulating populations of activated CD45RO + T cells which also showed low bcl-2 expression. In these patients, a significant correlation was seen between low bcl-2 expression by activated T cells and their apoptosis in culture (r = 0.94, p <0.001). These results suggest that the primary activation of T cells leads to the expansion of a population that is destined to perish unless rescued by some extrinsic event. Thus the suicide of CD45RO + T cells could be prevented by the addition ofinterleukin 2 to the culture medium which resulted in a concomitant increase in the bcl-2 expression of these cells. Alternatively, apoptosis was also prevented by coculturing the activated T lymphocytes with fibroblasts, which maintained the viability of lymphoid cells in a restinglike state but with low bcl-2 expression. The paradox that the CD45RO + population contains the primed/memory T cell pool yet expresses low bcl-2 and is susceptible to apoptosis can be reconciled by the observations that maintenance of T cell memory may be dependent on the continuous restimulation of T cells, which increases their bcl-2 expression. Furthermore, the propensity of CD45RO + T cells to extravasate may facilitate encounter with fibroblast-like cells in tissue stroma and thus be an important additional factor which promotes the survival of selected primed/memory T cells in vivo.

Infection of endothelial cells with an endothelial cell-tropic clinical isolate of cytomegalovirus (CMV), C1FE, induced enhanced production of the neutrophil chemoattractant C-X-C chemokines interleukin-8 and GROalpha. Infected endothelial cell supernatants induced neutrophil chemotaxis in a transendothelial migration assay. Neutrophils acquired the CMV structural protein pp65 following either coculture with infected endothelial cells or transmigration through infected endothelium. The lack of CMV p72 expression in the neutrophils indicated that viral replication had not occurred in these cells. Of importance, neutrophils acquired infectious CMV during transmigration across infected endothelium and were subsequently able to transmit infectious virus to fibroblasts. Thus, CMV-infected endothelial cells can recruit neutrophils by the secretion of C-X-C chemokines and can transmit the virus to them by direct cell-to-cell contact and during neutrophil transendothelial migration, suggesting that the neutrophil-endothelial cell interaction plays an important role in virus dissemination in vivo.

Virus‐induced alterations in the cellular expression of chemokines may be important in directing the migration of specific leucocyte subsets to sites of infection, thereby playing a pivotal role in viral pathogenesis. We show here that cytomegalovirus (CMV) infection of human fibroblasts resulted in significantly increased expression of the C‐X‐C or α‐chemokine interleukin‐8 (IL‐8), at both the mRNA and protein levels. Increased IL‐8 production was seen following infection with the high passage laboratory CMV strains AD169, Towne, or Davis, as well as the low passage clinical CMV isolates Toledo or C1F. The increase in IL‐8 production had functional consequences, as demonstrated by the ability of supernatants from CMV‐infected fibroblasts to significantly enhance neutrophil transendothelial migration. The latter was independent of alterations in adhesion molecule expression on the endothelial cells, and was abrogated by neutralizing antibodies specific for IL‐8. Direct infection of endothelium with the endothelial cell‐tropic CMV strain C1FE, also resulted in enhanced neutrophil transendothelial migration. Neutrophils play an important role in the dissemination of CMV throughout the body, and thus CMV‐induced neutrophil recruitment would be expected to enhance CMV dissemination. Increased production of chemokines in response to CMV infection could also disrupt the fine balance between a beneficial and a destructive immune response, thereby potentially contributing to pathology.

SUMMARYWe have previously demonstrated that human cytomegalovirus (CMV) binds the host protein fl2microglobulin (fl2m) from body fluids or from cell culture media. In this report we have examined the effect of the fl2m on viral infectivity. We have shown that the addition of human purified/~2m, or a fraction of foetal calf serum corresponding to bovine f12 m, to culture medium increased the amount of infectious extracellular CMV, compared to that from cells grown in serum-free medium. Metabolic labelling experiments demonstrated that this effect was not due to an increase in the amount of extracellular virus but to an increase in the infectivity of the virus present in extracellular fluids. We concluded that the binding of ]~2m by CMV increased its infectivity. We have shown that CMV and /~2m compete for binding sites on INTRODUCTIONHuman cytomegalovirus (CMV) is a ubiquitous agent which has a complex relationship with its host. We have previously reported that CMV grown in cell culture has the capacity to bind the host protein P2 microglobulin (fl2m) . The ]~2m binding capacity of CMV was found to reside in two viral envelope proteins, flzm BP1 and fl2m BP2 , and we have calculated that in the order of 105 molecules of fl2m were bound per infectious virus particle (McKeating et al., 1986). We have shown that in body fluids in vivo, CMV exists as flzm-coated particles . The binding offl2m to CMV was found to mask the viral antigenic determinants so that the viral glycoproteins could not be recognized by CMV-specific monoclonal antibodies (McKeating et al., 1986). Farthermore the flzm-coated virus found naturally in urine specimens could not be neutralized by hyperimmune globulin, human immune sera or murine monoclonal antibodies that could neutralize CMV grown in cell culture . We concluded that the binding of fl2m by CMV masked the important antigenic sites necessary for neutralization and postulated that the virus had evolved this mechanism of coating itself in a host protein as a means of evading the host immune response.

Cytotoxic T cell recognition of virus-infected cells requires the presentation of viral peptides by class I HLA molecules on the cell surface. We report here that cytomegalovirus (CMV) infection of human fibroblasts results in a progressive decrease in the cell surface expression of class I HLA and fl2-microglobulin (fl2m) such that in the late stages of infection the majority of infected cells have no detectable surface class I HLA. Coincident with decreased surface expression of class I HLA was an increase in his cytoplasmic expression. Confocal scanning laser microscopic analysis demonstrated that class I HLA and fl2m accumulate in a perinuclear compartment inside the CMV-infected cell. Our data thus support the concept that CMV infection induces altered transport of class I HLA to the cell surface. We suggest that the virus has evolved this mechanism as a strategy to avoid T cell recognition of infected cells.