Target Cells of HCMV in Cell Culture

An increasing number of cell culture models almost perfectly reflect the in vivo situation concerning susceptibility of the various cell types. Again, lymphocytes and granulocytes are among the few cell types that were not found to support replication of HCMV in vitro, although they may still act as a passive vehicle for HCMV transmission. On the contrary, the list of susceptible primary cell cultures is long, including skin or lung fibroblasts, vascular smooth muscle cells (Tumilowicz et al. 1985), retina pigment epithelial cells (Tugizov et al. 1996), placental trophoblast cells (Halwachs-Baumann et al. 1998), hepatocytes (Sinzger et al. 1999a), neuronal and glial brain cells (Poland et al. 1990), kidney epithelial cells (Heieren et al. 1988), monocyte-derived macrophages (Ibanez et al. 1991; Lathey and Spector 1991), monocyte-derived dendritic cells (Riegler et al. 2000), and vascular endothelial cells (Ho et al. 1984; Waldman et al. 1989). All of these primary cell types support the complete viral replication cycle, acquire a uniform cytomegalic appearance during the late replication phase and are finally lysed (Fig. 1b). In addition, limited replication can be achieved in a number of immortalized cell lines such as glioblastoma cells, teratocarcinoma cell lines or monocytic cell lines. However, some kind of differentiation is often necessary to render such cell lines supportive of a complete replication cycle (Shelbourn et al. 1989; Ibanez et al. 1991; Lathey and Spector 1991; Spiller et al. 1997; Sinclair and Sissons

Fig. 1 a Immunohistochemical evidence of productive infection in endothelial cells and smooth muscle cells in vivo, as indicated by focus formation within the respective cell layers. Brown nuclear signals, detection of HCMV immediate early antigens by indirect immunoperoxidase labeling; red cytoplasmic signals, detection of F.VIII-related antigen (endothelial cells) and actin (smooth muscle cells) by indirect immunoalkaline phosphatase labeling; blue nuclear signals, counterstaining with hematoxilin. b Phase contrast micrographs of HCMV-infected cell cultures. Irrespective of the great morphological differences between cultured cells prior to infection, HCMV productive replication results in uniform morphological appearance with cytomegaly and nuclear inclusions

Fig. 1 a Immunohistochemical evidence of productive infection in endothelial cells and smooth muscle cells in vivo, as indicated by focus formation within the respective cell layers. Brown nuclear signals, detection of HCMV immediate early antigens by indirect immunoperoxidase labeling; red cytoplasmic signals, detection of F.VIII-related antigen (endothelial cells) and actin (smooth muscle cells) by indirect immunoalkaline phosphatase labeling; blue nuclear signals, counterstaining with hematoxilin. b Phase contrast micrographs of HCMV-infected cell cultures. Irrespective of the great morphological differences between cultured cells prior to infection, HCMV productive replication results in uniform morphological appearance with cytomegaly and nuclear inclusions

2006). While in vivo analyses were apt to descriptively identify the cell types infected by HCMV in its natural host, cell culture models made it possible to address quantitative aspects regarding susceptibility and productivity, thus revealing striking differences between cells of different origin: skin or lung fibroblast have always been the standard cell type for isolation and propagation of HCMV from patient samples and are still the most efficient producer cell line irrespective of the virus strain (Mocarski et al. 2006). For certain HCMV strains, vascular endothelial cells are also sufficiently susceptible and productive to allow long-term propagation of certain virus strains by passaging cell-free supernatants of infected cultures (Digel and Sinzger 2006). Other cell cultures, e.g., monocyte-derived macrophages, are low-level productive (Sinzger et al. 2006) and hardly release sufficient amounts of infectious progeny to maintain the virus during repeated passaging of cell-free supernatant on the respective cell type.

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