Immune Evasion Proteins Enhance Cytomegalovirus Latency in the Lungs

Institute for Virology, University Medical Center of Johannes Gutenberg University, 55131 Mainz, Germany.
Journal of Virology (Impact Factor: 4.44). 08/2009; 83(19):10293-8. DOI: 10.1128/JVI.01143-09
Source: PubMed


CD8 T cells control cytomegalovirus (CMV) infection in bone marrow transplantation recipients and persist in latently infected
lungs as effector memory cells for continuous sensing of reactivated viral gene expression. Here we have addressed the question
of whether viral immunoevasins, glycoproteins that specifically interfere with antigen presentation to CD8 T cells, have an
impact on viral latency in the murine model. The data show that deletion of immunoevasin genes in murine CMV accelerates the
clearance of productive infection during hematopoietic reconstitution and leads to a reduced latent viral genome load, reduced
latency-associated viral transcription, and a lower incidence of recurrence in lung explants.

Download full-text


Available from: Christof Seckert
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: For recognition of infected cells by CD8 T cells, antigenic peptides are presented at the cell surface, bound to major histocompatibility complex class I (MHC-I) molecules. Downmodulation of cell surface MHC-I molecules is regarded as a hallmark function of cytomegalovirus-encoded immunoevasins. The molecular mechanisms by which immunoevasins interfere with the MHC-I pathway suggest, however, that this downmodulation may be secondary to an interruption of turnover replenishment and that hindrance of the vesicular transport of recently generated peptide-MHC (pMHC) complexes to the cell surface is the actual function of immunoevasins. Here we have used the model of murine cytomegalovirus (mCMV) infection to provide experimental evidence for this hypothesis. To quantitate pMHC complexes at the cell surface after infection in the presence and absence of immunoevasins, we generated the recombinant viruses mCMV-SIINFEKL and mCMV-Deltam06m152-SIINFEKL, respectively, expressing the K(b)-presented peptide SIINFEKL with early-phase kinetics in place of an immunodominant peptide of the viral carrier protein gp36.5/m164. The data revealed approximately 10,000 K(b) molecules presenting SIINFEKL in the absence of immunoevasins, which is an occupancy of approximately 10% of all cell surface K(b) molecules, whereas immunoevasins reduced this number to almost the detection limit. To selectively evaluate their effect on preexisting pMHC complexes, cells were exogenously loaded with SIINFEKL peptide shortly after infection with mCMV-SIINFEKA, in which endogenous presentation is prevented by an L174A mutation of the C-terminal MHC-I anchor residue. The data suggest that pMHC complexes present at the cell surface in advance of immunoevasin gene expression are downmodulated due to constitutive turnover in the absence of resupply.
    Full-text · Article · Nov 2009 · Journal of Virology
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In lung transplant patients undergoing immunosuppression, more than one human cytomegalovirus (HCMV) genotype may emerge during follow-up, and this could be critical for the outcome of HCMV infection. Up to now, many cases of infection with multiple HCMV genotypes were probably overlooked due to the limitations of the current genotyping approaches. We have now analyzed mixed-genotype infections in 17 clinical samples from 9 lung transplant patients using the highly sensitive ultradeep-pyrosequencing (UDPS) technology. UDPS genotyping was performed at three variable HCMV genes, coding for glycoprotein N (gN), glycoprotein O (gO), and UL139. Simultaneous analysis of a mean of 10,430 sequence reads per amplicon allowed the relative amounts of distinct genotypes in the samples to be determined down to 0.1% to 1% abundance. Complex mixtures of up to six different HCMV genotypes per sample were observed. In all samples, no more than two major genotypes accounted for at least 88% of the HCMV DNA load, and these were often accompanied by up to four low-abundance genotypes at frequencies of 0.1% to 8.6%. No evidence for the emergence of new genotypes or sequence changes over time was observed. However, analysis of different samples withdrawn from the same patients at different time points revealed that the relative levels of replication of the individual HCMV genotypes changed within a mixed-genotype population upon reemergence of the virus. Our data show for the first time that, similar to what has been hypothesized for the murine model, HCMV reactivation in humans seems to occur stochastically.
    Full-text · Article · Jul 2010 · Journal of Virology
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Cytomegaloviruses (CMVs) co-exist with their respective host species and have evolved to avoid their elimination by the hosts' immune effector mechanisms and to persist in a non-replicative state, known as viral latency. There is evidence to suggest that latency is nevertheless a highly dynamic condition during which episodes of viral gene desilencing, which can be viewed as incomplete reactivations, cause intermittent antigenic activity that stimulates CD8 memory-effector T cells and drives their clonal expansion. These T cells are supposed to terminate reactivation before completion of the productive viral cycle. In this view, CMVs do not "evade" their respective host's immune response but are actually held in check all the time, unless the host gets immunocompromised. Accordingly, CMV disease is typically a disease of the immunocompromised host only. Here we review current knowledge about the in vivo role of viral proteins involved in subverting the immune recognition of infected cells with focus on the CD8 T-cell response and viral interference with the MHC class-I pathway of antigenic peptide presentation. Whereas the intracellular functions of these "immune-evasion proteins" are known in molecular detail, knowledge of their in vivo role in CMV biology is only beginning to take shape. Experimental studies on the in vivo function of human CMV (hCMV) immune-evasion proteins prohibits, of course. Studying animal CMVs paradigmatically in the corresponding natural host is therefore used to identify principles from which the role of hCMV immune-evasion proteins can hopefully be inferred. Here we summarize recent insights gained primarily from the murine model.
    Full-text · Article · Oct 2010 · Virus Research
Show more