The nonclassical major histocompatibility complex (MHC) class I molecule HLA-E inhibits natural killer (NK) cell-mediated lysis by interacting with CD94/NKG2A receptors. Surface expression of HLA-E depends on binding of conserved peptides derived from MHC class I molecules. The same peptide is present in the leader sequence of the human cytomegalovirus (HCMV) glycoprotein UL40 (gpUL40). It is shown that, independently of the transporter associated with antigen processing, gpUL40 can up-regulate expression of HLA-E, which protects targets from NK cell lysis. While classical MHC class I molecules are down-regulated, HLA-E is up-regulated by HCMV. Induction of HLA-E surface expression by gpUL40 may represent an escape route for HCMV.

Natural killer (NK) cells are crucial in the control of cytomegalovirus infections in mice and humans. Here we show that the viral UL141 gene product has an immunomodulatory function that is associated with low-passage strains of human cytomegalovirus. UL141 mediated efficient protection of cells against killing by a wide range of human NK cell populations, including interferon-alpha-stimulated bulk cultures, polyclonal NK cell lines and most NK cell clones tested. Evasion of NK cell killing was mediated by UL141 blocking surface expression of CD155, which was previously identified as a ligand for NK cell-activating receptors CD226 (DNAM-1) and CD96 (TACTILE). The breadth of the UL141-mediated effect indicates that CD155 has a key role in regulating NK cell function.

Human cytomegalovirus (HCMV) causes lifelong, persistent infections and its survival is under intense, continuous selective pressure from the immune system. A key aspect of HCMV's capacity for survival lies in immune avoidance. In this context, cells undergoing productive infection exhibit remarkable resistance to natural killer (NK) cell-mediated cytolysis in vitro. To date, six genes encoding proteins (UL16, UL18, UL40, UL83, UL141 and UL142) and one encoding a microRNA (miR-UL112) have been identified as capable of suppressing NK cell recognition. Even though HCMV infection efficiently activates expression of ligands for the NK cell activating receptor NKG2D, at least three functions (UL16, UL142 and miR-UL112) act in concert to suppress presentation of these ligands on the cell surface. Although HCMV downregulates expression of endogenous MHC-I, it encodes an MHC-I homologue (UL18) and also upregulates the expression of cellular HLA-E through the action of UL40. The disruption of normal intercellular connections exposes ligands for NK cell activating receptors on the cell surface, notably CD155. HCMV overcomes this vulnerability by encoding a function (UL141) that acts post-translationally to suppress cell surface expression of CD155. The mechanisms by which HCMV systematically evades (or, more properly, modulates) NK cell recognition constitutes an area of growing understanding that is enhancing our appreciation of the basic mechanisms of NK cell function in humans.

The PML gene product is associated with a defined nuclear structure (10-20 per cell) known variously as PML-bodies, ND10, PODs or Kr bodies. Certain conditions are known to compromise the integrity of PML-bodies ; these include environmental stress (e.g. heat shock), a chromosomal translocationassociated acute promyelocytic leukaemia, and infection with certain viruses [including human cytomegalovirus (HCMV), herpes simplex virus type 1 and adenovirus]. Expression of the HCMV major immediate early (IE) protein (IE1 491aa ) is by itself sufficient to cause disruption of PML-bodies, resulting in the dispersal of the PML antigen uniformly throughout the nucleus. In uninfected cells undergoing mitosis PML is excluded from chromatin. However, both IE1 491aa and PML were observed to

The inhibitory leukocyte Ig-like receptor 1 (LIR-1, also known as ILT2, CD85j, or LILRB1) was identified by its high affinity for the human CMV (HCMV) MHC class I homolog gpUL18. The role of this LIR-1-gpUL18 interaction in modulating NK recognition during HCMV infection has previously not been clearly defined. In this study, LIR-1+ NKL cell-mediated cytotoxicity was shown to be inhibited by transduction of targets with a replication-deficient adenovirus vector encoding UL18 (RAd-UL18). Fibroblasts infected with an HCMV UL18 mutant (ΔUL18) also exhibited enhanced susceptibility to NKL killing relative to cells infected with the parental virus. In additional cytolysis assays, UL18-mediated protection was also evident in the context of adenovirus vector transduction and HCMV infection of autologous fibroblast targets using IFN-α-activated NK bulk cultures derived from a donor with a high frequency of LIR-1+ NK cells. A single LIR-1high NK clone derived from this donor was inhibited by UL18, while 3 of 24 clones were activated. CD107 mobilization assays revealed that LIR-1+ NK cells were consistently inhibited by UL18 in all tested donors, but this effect was often masked in the global response by UL18-mediated activation of a subset of LIR-1− NK cells. Although Ab-blocking experiments support UL18 inhibition being induced by a direct interaction with LIR-1, the UL18-mediated activation is LIR-1 independent.

Human cytomegalovirus (HCMV) UL141 induces protection against natural killer cell-mediated cytolysis by downregulating cell surface expression of CD155 (nectin-like molecule 5; poliovirus receptor), a ligand for the activating receptor DNAM-1 (CD226). However, DNAM-1 is also recognized to bind a second ligand, CD112 (nectin-2). We now show that HCMV targets CD112 for proteasome-mediated degradation by 48 h post-infection, thus removing both activating ligands for DNAM-1 from the cell surface during productive infection. Significantly, cell surface expression of both CD112 and CD155 was restored when UL141 was deleted from the HCMV genome. While gpUL141 alone is sufficient to mediate retention of CD155 in the endoplasmic reticulum, UL141 requires assistance from additional HCMV-encoded functions to suppress expression of CD112.

Human cytomegalovirus (HCMV) is a clinically important herpesvirus associated with severe disease following congenital infection and in immunocompromised individuals. As a herpesvirus, primary infection is accompanied by lifelong persistence during which the infection must be controlled by continuous host immune surveillance. HCMV has the largest genome of any characterized human virus (ϳ236 kb) and is predicted to encode on the order of 165 potential open reading frames (15). Systematic deletion of individual open reading frames from the Towne strain revealed that only 45 are essential for virus replication in vitro; thus, accessory genes account for most of the HCMV coding capacity (16). While the functions of most of these genes have not been determined, a significant number have been implicated in the targeting of both the innate and adaptive host immune responses (40). HCMV has also recently been shown to express microRNAs during productive infection that also have the potential to modulate host cell gene expression (17,21,43). A high-throughput proteomic approach was used in this study with a view to providing further insight into how the virus may modulate its host cell.HCMV replicates slowly in permissive human fibroblasts, with gene expression conventionally being divided into three phases: immediate-early (IE), early, and late (reviewed in reference 40). Early-phase transcription precedes viral DNA replication (initiates at 16 to 24 h postinfection [hpi]), with significant virus production detected from 72 hpi and peaking at approximately 144 hpi. Productive HCMV infection is associated with an overall stimulation of both cellular transcription and translation (50). Virion binding (13, 59), release of virion tegument proteins following virion fusion (6, 36), and de novo expression of powerful transcriptional regulators (most notably, IE2 and IE1) during infection all modulate cellular gene expression. Following infection, while cellular proteins associated with DNA metabolism are induced, host cell cyclins are dysregulated and licensing of host cell DNA replication is inhibited, resulting in a "pseudo-G 1 " environment compatible with efficient virus DNA replication (3,5,25). Microarray experiments have proved highly informative in revealing the dynamic regulation of steady-state levels of cellular transcripts, both positively and negatively, during the course of infection (7,26,48,65,66). HCMV is known not only to regulate transcriptional initiation but also to control RNA processing (1,9,14,20,35,63), translation, and posttranslational modification and protein trafficking (31,34,44,54,61). The result of many of these processes is liable to be an alteration of host cell protein levels.

Thyrotropin-thyrotropin receptor complexes Disulphide-linked subunit (SDS-polyacrylamide gel electrophoresis)