Expansion of the CD8 T-cell memory pool, also known as 'memory inflation', for certain but not all viral epitopes in latently infected host tissues is a special feature of the immune response to cytomegalovirus. The L d -presented murine cytomegalovirus (mCMV) immediate-early (IE) 1 peptide is the prototype of an epitope that is associated with memory inflation. Based on the detection of IE1 transcripts in latently infected lungs it was previously proposed that episodes of viral gene expression and antigenic activity due to desilencing of a limited number of viral genes may drive epitope-specific memory inflation. This would imply direct antigen presentation through latently infected host tissue cells rather than cell death-associated cross-presentation of viral antigens derived from productively infected cells through uninfected, professional antigenpresenting cells (profAPCs). To address the role of bone marrow-derived profAPCs in CD8 T-cell priming and memory to mCMV, we have used here a combined sex-mismatched and MHC class-I mismatched dual-marker bone marrow chimera model in which presentation of the IE1 epitope is restricted to donor-derived sry + L d+ cells of haematopoietic differentiation lineages. Successful CD8 T-cell priming specific for the L d -and D d -presented inflationary epitopes IE1 and m164, respectively, but selective failure in IE1 epitope-specific memory inflation in these chimeras indicates different modes of antigen presentation involved in CD8 T-cell priming and memory inflation. These data suggest that memory inflation during mCMV latency requires expression of the epitope-presenting MHC class-I molecule by latently infected non-haematopoietic host tissue cells and thus predicts a role for direct antigen presentation in memory inflation. INTRODUCTIONIt is current opinion that priming of CD8 T-cells during acute viral infections is accomplished mainly by uninfected professional antigen-presenting cells (profAPCs) that take up and 'cross-present' viral antigens derived from infected cells undergoing infection-associated cell death (den Haan & Bevan, 2001; Heath & Carbone, 2001;Kurts et al., 2010;Shen & Rock, 2006). For the infection with murine cytomegalovirus (mCMV), comparably efficient priming of CD8 T-cells in the presence and absence of 'viral inhibitors of direct antigen presentation', known as immunoevasins (for reviews, see Doom & Hill, 2008; Hansen & Bouvier, 2009;Lemmermann et al., 2011a;Reddehase, 2002), provided a reasonable argument for priming by cross-presentation (Böhm et al., 2008;Gold et al., 2002;Munks et al., 2007). More direct evidence for cross-presentation of mCMV epitopes was provided only recently by in vivo priming of CD8 T-cells with MHC class-I (MHC-I)-deficient fibroblasts infected with a spreaddefective virus mutant, mCMV-DgL, conditions which plausibly prevent any direct antigen presentation (Snyder et al., 2010). A potent cross-presenting cell type is the CD8 + CD11c + subset of dendritic cells (DCs) (Allan et al., 2003;Belz et al., 2004;Schnorrer et al...

Human Thy-1 (CD90) has been shown to mediate adhesion of inflammatory cells to activated microvascular endothelial cells via interaction with Mac-1 (CD11b/CD18) in vitro. Since there are no data showing the physiological relevance of Thy-1 for the recruitment of inflammatory cells in vivo, different inflammation models were investigated in Thy-1-deficient mice and littermate controls. In thioglycollate-induced peritonitis, the number of neutrophils and monocytes was significantly diminished in Thy-1-deficient mice. During acute lung inflammation, the extravasation of eosinophils and monocytes into the lung was significantly reduced in Thy-1-deficient mice. Moreover, during chronic lung inflammation, the influx of eosinophils and monocytes was also strongly decreased. These effects were independent of Thy-1 expression on T cells, as shown by the transplantation of WT BM into the Thy-1-deficient mice. In spite of the strong Thy-1 expression on T cells in the chimeric mice, the extravasation of the inflammatory cells in these mice was significantly diminished, compared to control mice. Finally, the altered number and composition of infiltrating leukocytes in Thy-1-deficient mice modified the chemokine/cytokine and protease expression at the site of inflammation. In conclusion, Thy-1 is involved in the control of inflammatory cell recruitment and, thus, also in conditioning the inflammatory microenvironment.Key words: Extravasation . Inflammation . Thy-1 Supporting Information available online IntroductionThe recruitment of inflammatory cells to sites of inflammation plays an important role in the pathogenesis of several inflammatory diseases. Leukocyte adhesion to endothelial cells (ECs) follows a multistep process, including the capture of free leukocytes out of the blood stream, rolling, firm adhesion, and transendothelial diapedesis. The importance of several adhesion molecules in this series of events has been described previously [1]. In ICAM-1-deficient mice, neutrophil recruitment was significantly reduced, but it was not completely blocked in a chemical peritonitis model or in a lipopolysaccharide 645(LPS)-induced airway inflammation model, indicating the involvement of additional adhesion molecules [2,3]. Furthermore, leukocyte recruitment in experimental colitis was not affected by blocking ICAM-1 or MadCAM, whereas the blocking of VCAM-1 resulted in a significant attenuation of colitis [4]. Thus, under specific inflammatory conditions, certain adhesion molecules mediate adhesion and transmigration of leukocytes into the perivascular tissue.Recently, human Thy-1 expressed on ECs was identified as an adhesion molecule mediating the binding of neutrophils and monocytes to activated microvascular ECs [5]. Thy-1 is a highly glycosylated GPI-anchored surface protein and a member of the immunoglobulin superfamily [6,7,8]. In humans, Thy-1 is expressed on ECs at sites of inflammation or in tumours whereas ECs do not express Thy-1 in healthy tissue [5,9]. Thy-1 is also expressed on fibroblasts, neurons, and a su...

Reactivation of latent cytomegalovirus (CMV) poses a clinical problem in transiently immunocompromised recipients of hematopoietic cell (HC) transplantation (HCT) by viral histopathology that results in multiple organ manifestations. Compared to autologous HCT and to syngeneic HCT performed with identical twins as HC donor and recipient, lethal outcome of CMV infection is more frequent in allogeneic HCT with MHC/HLA or minor histocompatibility loci mismatch between donor and recipient.It is an open question if a graft-vs.-host (GvH) reaction exacerbates CMV disease, or if CMV exacerbates GvH disease (GvHD), or if interference is mutual. Here we have used a mouse model of experimental HCT and murine CMV (mCMV) infection with an MHC class-I mismatch by gene deletion, so that either HCT donor or recipient lack a single MHC class-I molecule, specifically H-2 L d . This particular immunogenetic disparity has the additional advantage that it allows to experimentally separate GvH reaction of donor-derived T cells against recipient's tissues from host-vs.-graft (HvG) reaction of residual recipient-derived T cells against the transplanted HC and their progeny. While in HvG-HCT with L d -plus donors and L d -minus recipients almost all infected recipients were found to control the infection and survived, almost all infected recipients died of uncontrolled virus replication and consequent multiple-organ viral histopathology in case of GvH-HCT with L d -minus donors and L d -plus recipients. Unexpectedly, although anti-L d -reactive CD8 + T cells were detected, mortality was not found to be associated with GvHD histopathology. By comparing HvG-HCT and GvH-HCT, investigation into the mechanism revealed an inefficient reconstitution of antiviral high-avidity CD8 + T cells, associated with lack of formation of protective nodular inflammatory foci (NIF) in host tissue, selectively in GvH-HCT. Most notably, mice infected with an immune evasion gene deletion mutant of mCMV survived under otherwise identical GvH-HCT conditions. Survival was associated with enhanced antigen presentation and formation of protective NIF by antiviral CD8 + T Holtappels et al.Inefficient Antiviral Control After Allogeneic-HCT cells that control the infection and prevent viral histopathology. This is an impressive example of lethal viral disease in HCT recipients based on a failure of the immune control of CMV infection due to viral immune evasion in concert with an MHC class-I mismatch.

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