Inhibition of B cell receptor signaling induced by the human adenovirus species D E3/49K protein.

Introduction: The early transcription unit 3 (E3) of human adenoviruses (HAdVs) encodes several immunoevasins, including the E3/49K protein, which is unique for species D of HAdVs. It is expressed as surface transmembrane protein and shed. E3/49K of HAdV-D64 binds to the protein tyrosine phosphatase surface receptor CD45, thereby modulating activation of T and NK cells. Methods: Considering that E3/49K represents the most polymorphic viral protein among species D HAdVs, we demonstrate here that all tested E3/49K orthologs bind to the immunologically important regulator CD45. Thus, this feature is conserved regardless of the pathological associations of the respective HAdV types. Results: It appeared that modulation of CD45 is a unique property restricted to HAdVs of species D. Moreover, E3/49K treatment inhibited B cell receptor (BCR) signaling and impaired BCR signal phenotypes. The latter were highly comparable to B cells having defects in the expression of CD45, suggesting E3/49K as a potential tool to investigate CD45 specific functions. Conclusion: We identified B cells as new direct target of E3/49K-mediated immune modulation, representing a novel viral immunosubversive mechanism.

Arsenic trioxide impacts hepatitis B virus core nuclear localization and efficiently interferes with HBV infection.

The key to a curative treatment of hepatitis B virus (HBV) infection is the eradication of the intranuclear episomal covalently closed circular DNA (cccDNA), the stable persistence reservoir of HBV. Currently, established therapies can only limit HBV replication but fail to tackle the cccDNA. Thus, novel therapeutic approaches toward curative treatment are urgently needed. Recent publications indicated a strong association between the HBV core protein SUMOylation and the association with promyelocytic leukemia nuclear bodies (PML-NBs) on relaxed circular DNA to cccDNA conversion. We propose that interference with the cellular SUMOylation system and PML-NB integrity using arsenic trioxide provides a useful tool in the treatment of HBV infection. Our study showed a significant reduction in HBV-infected cells, core protein levels, HBV mRNA, and total DNA. Additionally, a reduction, albeit to a limited extent, of HBV cccDNA could be observed. Furthermore, this interference was also applied for the treatment of an established HBV infection, characterized by a stably present nuclear pool of cccDNA. Arsenic trioxide (ATO) treatment not only changed the amount of expressed HBV core protein but also induced a distinct relocalization to an extranuclear phenotype during infection. Moreover, ATO treatment resulted in the redistribution of transfected HBV core protein away from PML-NBs, a phenotype similar to that previously observed with SUMOylation-deficient HBV core. Taken together, these findings revealed the inhibition of HBV replication by ATO treatment during several steps of the viral replication cycle, including viral entry into the nucleus as well as cccDNA formation and maintenance. We propose ATO as a novel prospective treatment option for further pre-clinical and clinical studies against HBV infection. IMPORTANCE: The main challenge for the achievement of a functional cure for hepatitis B virus (HBV) is the covalently closed circular DNA (cccDNA), the highly stable persistence reservoir of HBV, which is maintained by further rounds of infection with newly generated progeny viruses or by intracellular recycling of mature nucleocapsids. Eradication of the cccDNA is considered to be the holy grail for HBV curative treatment; however, current therapeutic approaches fail to directly tackle this HBV persistence reservoir. The molecular effect of arsenic trioxide (ATO) on HBV infection, protein expression, and cccDNA formation and maintenance, however, has not been characterized and understood until now. In this study, we reveal ATO treatment as a novel and innovative therapeutic approach against HBV infections, repressing viral gene expression and replication as well as the stable cccDNA pool at low micromolar concentrations by affecting the cellular function of promyelocytic leukemia nuclear bodies.

Diverse cytomegalovirus US11 antagonism and MHC-A evasion strategies reveal a tit-for-tat coevolutionary arms race in hominids.

Recurrent, ancient arms races between viruses and hosts have shaped both host immunological defense strategies as well as viral countermeasures. One such battle is waged by the glycoprotein US11 encoded by the persisting human cytomegalovirus. US11 mediates degradation of major histocompatibility class I (MHC-I) molecules to prevent CD8+ T-cell activation. Here, we studied the consequences of the arms race between US11 and primate MHC-A proteins, leading us to uncover a tit-for-tat coevolution and its impact on MHC-A diversification. We found that US11 spurred MHC-A adaptation to evade viral antagonism: In an ancestor of great apes, the MHC-A A2 lineage acquired a Pro184Ala mutation, which confers resistance against the ancestral US11 targeting strategy. In response, US11 deployed a unique low-complexity region (LCR), which exploits the MHC-I peptide loading complex to target the MHC-A2 peptide-binding groove. In addition, the global spread of the human HLA-A*02 allelic family prompted US11 to employ a superior LCR strategy with an optimally fitting peptide mimetic that specifically antagonizes HLA-A*02. Thus, despite cytomegaloviruses low pathogenic potential, the increasing commitment of US11 to MHC-A has significantly promoted diversification of MHC-A in hominids.

Deletion of the non-adjacent genes UL148 and UL148D impairs human cytomegalovirus-mediated TNF receptor 2 surface upregulation.

Human cytomegalovirus (HCMV) is a prototypical ß-herpesvirus which frequently causes morbidity and mortality in individuals with immature, suppressed, or senescent immunity. HCMV is sensed by various pattern recognition receptors, leading to the secretion of pro-inflammatory cytokines including tumor necrosis factor alpha (TNFα). TNFα binds to two distinct trimeric receptors: TNF receptor (TNFR) 1 and TNFR2, which differ in regard to their expression profiles, affinities for soluble and membrane-bound TNFα, and down-stream signaling pathways. While both TNF receptors engage NFκB signaling, only the nearly ubiquitously expressed TNFR1 exhibits a death domain that mediates TRADD/FADD-dependent caspase activation. Under steady-state conditions, TNFR2 expression is mainly restricted to immune cells where it predominantly submits pro-survival, proliferation-stimulating, and immune-regulatory signals. Based on the observation that HCMV-infected cells show enhanced binding of TNFα, we explored the interplay between HCMV and TNFR2. As expected, uninfected fibroblasts did not show detectable levels of TNFR2 on the surface. Intriguingly, however, HCMV infection increased TNFR2 surface levels of fibroblasts. Using HCMV variants and BACmid-derived clones either harboring or lacking the ULb' region, an association between TNFR2 upregulation and the presence of the ULb' genome region became evident. Applying a comprehensive set of ULb' gene block and single gene deletion mutants, we observed that HCMV mutants in which the non-adjacent genes UL148 or UL148D had been deleted show an impaired ability to upregulate TNFR2, coinciding with an inverse regulation of TACE/ADAM17.

Class switch toward noninflammatory, spike-specific IgG4 antibodies after repeated SARS-CoV-2 mRNA vaccination.

RNA vaccines are efficient preventive measures to combat the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic. High levels of neutralizing SARS-CoV-2 antibodies are an important component of vaccine-induced immunity. Shortly after the initial two mRNA vaccine doses, the immunoglobulin G (IgG) response mainly consists of the proinflammatory subclasses IgG1 and IgG3. Here, we report that several months after the second vaccination, SARS-CoV-2-specific antibodies were increasingly composed of noninflammatory IgG4, which were further boosted by a third mRNA vaccination and/or SARS-CoV-2 variant breakthrough infections. IgG4 antibodies among all spike-specific IgG antibodies rose, on average, from 0.04% shortly after the second vaccination to 19.27% late after the third vaccination. This induction of IgG4 antibodies was not observed after homologous or heterologous SARS-CoV-2 vaccination with adenoviral vectors. Single-cell sequencing and flow cytometry revealed substantial frequencies of IgG4-switched B cells within the spike-binding memory B cell population [median of 14.4%; interquartile range (IQR) of 6.7 to 18.1%] compared with the overall memory B cell repertoire (median of 1.3%; IQR of 0.9 to 2.2%) after three immunizations. This class switch was associated with a reduced capacity of the spike-specific antibodies to mediate antibody-dependent cellular phagocytosis and complement deposition. Because Fc-mediated effector functions are critical for antiviral immunity, these findings may have consequences for the choice and timing of vaccination regimens using mRNA vaccines, including future booster immunizations against SARS-CoV-2.

Do common infections trigger disease-onset or -severity in CTLA-4 insufficiency?

Purpose: Heterozygous mutations in CTLA4 lead to an inborn error of immunity characterized by immune dysregulation and immunodeficiency, known as CTLA-4 insufficiency. Cohort studies on CTLA4 mutation carriers showed a reduced penetrance (around 70%) and variable disease expressivity, suggesting the presence of modifying factors. It is well studied that infections can trigger autoimmunity in humans, especially in combination with a genetic predisposition. Methods: To investigate whether specific infections or the presence of specific persisting pathogens are associated with disease onset or severity in CTLA-4 insufficiency, we have examined the humoral immune response in 13 CTLA4 mutation carriers, seven without clinical manifestation and six with autoimmune manifestations, but without immunoglobulin replacement therapy against cytomegalovirus (CMV), Epstein-Barr virus (EBV), herpes simplex virus 1/2 (HSV 1/2), parvovirus B19 and Toxoplasma gondii. Additionally, we have measured FcγRIII/CD16A activation by EBV-specific IgG antibodies to examine the functional capabilities of immunoglobulins produced by CTLA4 mutation carriers. Results: The seroprevalence between affected and unaffected CTLA4 mutation carriers did not differ significantly for the examined pathogens. Additionally, we show here that CTLA4 mutation carriers produce EBV-specific IgG, which are unimpaired in activating FcγRIII/CD16A. Conclusions: Our results show that the investigated pathogens are very unlikely to trigger the disease onset in CTLA-4-insufficient individuals, and their prevalence is not correlated with disease severity or expressivity.

A Novel, Broad-Acting Peptide Inhibitor of Double-Stranded DNA Virus Gene Expression and Replication.

Viral infections are a global disease burden with only a limited number of antiviral agents available. Due to newly emerging viral pathogens and increasing occurrence of drug resistance, there is a continuous need for additional therapeutic options, preferably with extended target range. In the present study, we describe a novel antiviral peptide with broad activity against several double-stranded DNA viruses. The 22-mer peptide TAT-I24 potently neutralized viruses such as herpes simplex viruses, adenovirus type 5, cytomegalovirus, vaccinia virus, and simian virus 40 in cell culture models, while being less active against RNA viruses. The peptide TAT-I24 therefore represents a novel and promising drug candidate for use against double-stranded DNA viruses.

Pharmacological Inhibition of Acid Sphingomyelinase Prevents Uptake of SARS-CoV-2 by Epithelial Cells.

The acid sphingomyelinase/ceramide system plays an important role in bacterial and viral infections. Here, we report that either pharmacological inhibition of acid sphingomyelinase with amitriptyline, imipramine, fluoxetine, sertraline, escitalopram, or maprotiline or genetic downregulation of the enzyme prevents infection of cultured cells or freshy isolated human nasal epithelial cells with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) or vesicular stomatitis virus (VSV) pseudoviral particles (pp-VSV) presenting SARS-CoV-2 spike protein (pp-VSV-SARS-CoV-2 spike), a bona fide system mimicking SARS-CoV-2 infection. Infection activates acid sphingomyelinase and triggers a release of ceramide on the cell surface. Neutralization or consumption of surface ceramide reduces infection with pp-VSV-SARS-CoV-2 spike. Treating volunteers with a low dose of amitriptyline prevents infection of freshly isolated nasal epithelial cells with pp-VSV-SARS-CoV-2 spike. The data justify clinical studies investigating whether amitriptyline, a safe drug used clinically for almost 60 years, or other antidepressants that functionally block acid sphingomyelinase prevent SARS-CoV-2 infection.

COVID-19 in a Severely Immunosuppressed Patient With Life-Threatening Eosinophilic Granulomatosis With Polyangiitis.

Immunosuppressive therapies increase the susceptibility of patients to infections. The current pandemic with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) compels clinicians to develop recommendations for successful clinical management and surveillance of immunocompromised patients at high risk for severe disease progression. With only few case studies published on SARS-CoV-2 infection in patients with rheumatic diseases, we report a 25-year-old male who developed moderate coronavirus disease 2019 (COVID-19) with fever, mild dyspnea, and no major complications despite having received high-dose prednisolone, cyclophosphamide, and rituximab for the treatment of highly active, life-threatening eosinophilic granulomatosis with polyangiitis (EGPA).

Trigger-dependent differences determine therapeutic outcome in murine primary hemophagocytic lymphohistiocytosis.

Familial hemophagocytic lymphohistiocytosis (FHL) is a hyperinflammatory syndrome affecting patients with genetic cytotoxicity defects. Perforin-deficient (PKO) mice recapitulate the full clinical picture of FHL after infection with lymphocytic choriomeningitis virus (LCMV). Hyperactivated CD8+ T cells and IFN-γ have been identified as the key drivers of FHL and represent targets for therapeutic interventions. However, the response of patients is variable. This could be due to trigger-dependent differences in pathogenesis, which is difficult to address in FHL patients, since the trigger frequently escapes detection. We established an alternative FHL model using intravenous infection of PKO mice with murine CMV (MCMV)Smith . PKO mice developed acute FHL after both infections and fulfilled HLH diagnostic criteria accompanied by excessive IFN-γ production by disease-inducing T cells, that enrich in the BM. However, direct comparison of the two infection models disclosed trigger-dependence of FHL progression and revealed a higher contribution of CD4 T cells and NK cells to IFN-γ production after MCMV infection. Importantly, therapeutic intervention by IFN-γ neutralization or CD8+ T-cell depletion had less benefit in MCMV-triggered FHL compared to LCMV-triggered FHL, likely due to MCMV-induced cytopathology. Thus, the context of the specific triggering viral infection can impact the success of targeted immunotherapeutic HLH control.

HCMV Infection in a Mesenchymal Stem Cell Niche: Differential Impact on the Development of NK Cells versus ILC3.

Human cytomegalovirus (HCMV) is highly prevalent in most populations worldwide and has a major influence on shaping the human immune system. Natural killer (NK) cells are important antiviral effectors that adapt to HCMV infection by expansion of virus-specific effector/memory cells. The impact of HCMV infection on the development of NK cells and innate lymphoid cells (ILC) in general is less well understood. In this context, we have recently established a novel in vitro platform to study human NK cell development in a stem cell niche based on human bone marrow-derived mesenchymal stem cells (MSC). Here, the system was modified by infecting MSC with HCMV to study the influence of virus infection on NK/ILC development. We show that cord blood-derived hematopoietic progenitor cells are successfully differentiated into mature CD56+CD94+NKG2A+ NK cells on HCMV-infected MSC with significant higher anti-viral cytokine production compared to NK cells developing on non-infected MSC. Furthermore, the generation of ILC3, characterized by expression of the signature transcription factor RAR-related orphan receptor gamma (RORγt) and the production of IL-22, was strongly impaired by HCMV infection. These observations are clinically relevant, given that ILC3 are associated with protection from graft-versus-host disease (GvHD) following stem cell transplantation and HCMV reactivation in turn is associated with increased incidence of GvHD.

Fc-Fusion Drugs Have FcγR/C1q Binding and Signaling Properties That May Affect Their Immunogenicity.

Fusing the human immunoglobulin G1 (IgG1) constant region (Fc-domain) to therapeutic proteins or peptides increases their circulating plasma half-life via neonatal Fc receptor (FcRn) binding and recycling. However, Fc-mediated interactions with other molecules including complement C1q and Fc gamma receptors (FcγRs) can have immunological consequences and the potential to modulate the immunogenicity of Fc-fusion therapeutics. In a comparative study, we carried out a comprehensive assessment of Fc-mediated interactions for five FDA-approved Fc-fusion therapeutics. C1q binding and complement activation were measured by ELISA, while FcγR binding and signaling were evaluated using BW5147:FcγR-ζ reporter cell lines. We demonstrate that FIX-Fc and FVIII-Fc bound C1q as well as activating and inhibitory FcγRs (I, IIA, IIB, IIIA). These coagulation factor Fc-fusions also signaled via FcγRIIIA, and to a lesser extent via FcγRI and FcγRIIB. TNFR-Fc and CTLA4-Fc bound FcγRI, while TNFR-Fc also bound FcγRIIIA, but these interactions did not result in FcγR signaling. Our comprehensive assessment demonstrates that (i) different Fc-fusion drugs have distinct C1q/FcγR binding and signaling properties, (ii) FcγR binding does not predict signaling, and (iii) the fusion partner (effector molecule) can influence Fc-mediated interactions.

The complex of MCMV proteins and MHC class I evades NK cell control and drives the evolution of virus-specific activating Ly49 receptors.

CMVs efficiently target MHC I molecules to avoid recognition by cytotoxic T cells. However, the lack of MHC I on the cell surface renders the infected cell susceptible to NK cell killing upon missing self recognition. To counter this, mouse CMV (MCMV) rescues some MHC I molecules to engage inhibitory Ly49 receptors. Here we identify a new viral protein, MATp1, that is essential for MHC I surface rescue. Rescued altered-self MHC I molecules show increased affinity to inhibitory Ly49 receptors, resulting in inhibition of NK cells despite substantially reduced MHC I surface levels. This enables the virus to evade recognition by licensed NK cells. During evolution, this novel viral immune evasion mechanism could have prompted the development of activating NK cell receptors that are specific for MATp1-modified altered-self MHC I molecules. Our study solves a long-standing conundrum of how MCMV avoids recognition by NK cells, unravels a fundamental new viral immune evasion mechanism, and demonstrates how this forced the evolution of virus-specific activating MHC I-restricted Ly49 receptors.

Kinetics of Torque Teno Virus-DNA Plasma Load Predict Rejection in Lung Transplant Recipients.

BACKGROUND: Lung transplantation is the only therapeutic option in end-stage lung diseases; however, survival after transplantation is limited by acute and chronic rejection or infectious events being results of inappropriate immunosuppression. Torque Teno Viruses (TTVs) are ubiquitous DNA viruses in humans but not found to be causative for any disease. However, some reports suggest that TTV-DNA levels reflect the grade of immunosuppression with higher levels being found in more immunosuppressed individuals. METHODS: We investigated the TTV-DNA levels in 34 lung transplant recipients within their first year after transplantation by quantitative real-time polymerase chain reaction. Clinical data were extracted from charts. RESULTS: In accordance with previous results TTV-DNA levels increase after lung transplantation reaching a steady state after 3 months. The TTV-DNA levels were not correlated with immunosuppressive trough levels and a selective increase was not observed with other DNA viruses. In steady state TTV-DNA levels were significantly higher in patients with infectious complications compared to the group of patients without. Additionally, TTV-DNA levels decreased significantly before biopsy-proven rejection. Sensitivity of a 10-fold decrease in TTV-DNA levels for a subsequent rejection episode was 0.74 with a specificity of 0.99. CONCLUSIONS: In summary, TTV-DNA might be used as an additional tool to monitor immunosuppression in lung transplant recipients. Higher TTV-DNA levels reflect more intense immunosuppression, whereas the TTV-DNA kinetic (ie, decrease of TTV-DNA levels) indicate rejection.

Selective Engagement of FcγRIV by a M2e-Specific Single Domain Antibody Construct Protects Against Influenza A Virus Infection.

Lower respiratory tract infections, such as infections caused by influenza A viruses, are a constant threat for public health. Antivirals are indispensable to control disease caused by epidemic as well as pandemic influenza A. We developed a novel anti-influenza A virus approach based on an engineered single-domain antibody (VHH) construct that can selectively recruit innate immune cells to the sites of virus replication. This protective construct comprises two VHHs. One VHH binds with nanomolar affinity to the conserved influenza A matrix protein 2 (M2) ectodomain (M2e). Co-crystal structure analysis revealed that the complementarity determining regions 2 and 3 of this VHH embrace M2e. The second selected VHH specifically binds to the mouse Fcγ Receptor IV (FcγRIV) and was genetically fused to the M2e-specific VHH, which resulted in a bi-specific VHH-based construct that could be efficiently expressed in Pichia pastoris. In the presence of M2 expressing or influenza A virus-infected target cells, this single domain antibody construct selectively activated the mouse FcγRIV. Moreover, intranasal delivery of this bispecific FcγRIV-engaging VHH construct protected wild type but not FcγRIV-/- mice against challenge with an H3N2 influenza virus. These results provide proof of concept that VHHs directed against a surface exposed viral antigen can be readily armed with effector functions that trigger protective antiviral activity beyond direct virus neutralization.

Human MxB Protein Is a Pan-herpesvirus Restriction Factor.

Herpesvirus infections are highly prevalent in the human population and persist for life. They are often acquired subclinically but potentially progress to life-threatening diseases in immunocompromised individuals. The interferon system is indispensable for the control of herpesviral replication. However, the responsible antiviral effector mechanisms are not well characterized. The type I interferon-induced, human myxovirus resistance 2 (MX2) gene product MxB, a dynamin-like large GTPase, has recently been identified as a potent inhibitor of HIV-1. We now show that MxB also interferes with an early step of herpesvirus replication, affecting alpha-, beta-, and gammaherpesviruses before or at the time of immediate early gene expression. Defined MxB mutants influencing GTP binding and hydrolysis revealed that the effector mechanism against herpesviruses is thoroughly different from that against HIV-1. Overall, our findings demonstrate that MxB serves as a broadly acting intracellular restriction factor that controls the establishment of not only retrovirus but also herpesvirus infection of all three subfamilies.IMPORTANCE Human herpesviruses pose a constant threat to human health. Reactivation of persisting herpesvirus infections, particularly in immunocompromised individuals and the elderly, can cause severe diseases, such as zoster, pneumonia, encephalitis, or cancer. The interferon system is relevant for the control of herpesvirus replication as exemplified by fatal disease outcomes in patients with primary immunodeficiencies. Here, we describe the interferon-induced, human MX2 gene product MxB as an efficient restriction factor of alpha-, beta-, and gammaherpesviruses. MxB has previously been described as an inhibitor of HIV-1. Importantly, our mutational analyses of MxB reveal an antiviral mechanism of herpesvirus restriction distinct from that against HIV-1. Thus, the dynamin-like MxB GTPase serves as a broadly acting intracellular restriction factor that controls retrovirus as well as herpesvirus infections.

An A/U-Rich Enhancer Region Is Required for High-Level Protein Secretion through the HlyA Type I Secretion System.

Efficient protein secretion is often a valuable alternative to classic cellular expression to obtain homogenous protein samples. Early on, bacterial type I secretion systems (T1SS) were employed to allow heterologous secretion of fusion proteins. However, this approach was not fully exploited, as many proteins could not be secreted at all or only at low levels. Here, we present an engineered microbial secretion system which allows the effective production of proteins up to a molecular mass of 88 kDa. This system is based on the hemolysin A (HlyA) T1SS of the Gram-negative bacterium Escherichia coli, which exports polypeptides when fused to a hemolysin secretion signal. We identified an A/U-rich enhancer region upstream of hlyA required for effective expression and secretion of selected heterologous proteins irrespective of their prokaryotic, viral, or eukaryotic origin. We further demonstrate that the ribosomal protein S1 binds to the hlyA A/U-rich enhancer region and that this region is involved in the high yields of secretion of functional proteins, like maltose-binding protein or human interferon alpha-2.IMPORTANCE A 5' untranslated region of the mRNA of substrates of type I secretion systems (T1SS) drastically enhanced the secretion efficiency of the endogenously secreted protein. The identification of ribosomal protein S1 as the interaction partner of this 5' untranslated region provides a rationale for the enhancement. This strategy furthermore can be transferred to fusion proteins allowing a broader, and eventually a more general, application of this system for secreting heterologous fusion proteins.

Elusive Role of the CD94/NKG2C NK Cell Receptor in the Response to Cytomegalovirus: Novel Experimental Observations in a Reporter Cell System.

Human cytomegalovirus (HCMV) infection promotes the differentiation and persistent expansion of a mature NK cell subset, which displays high surface levels of the activating CD94/NKG2C NK cell receptor, together with additional distinctive phenotypic and functional features. The mechanisms underlying the development of adaptive NK cells remain uncertain but some observations support the involvement of a cognate interaction of CD94/NKG2C with ligand(s) displayed by HCMV-infected cells. To approach this issue, the heterodimer and its adaptor (DAP12) were expressed in the human Jurkat leukemia T cell line; signaling was detected by transfection of a reporter plasmid encoding for Luciferase (Luc) under NFAT/AP1-dependent control. Engagement of the receptor by solid-phase bound CD94- or NKG2C-specific monoclonal antibodies (mAbs) triggered Luc expression. Moreover, reporter activation was detectable upon interaction with HLA-E+ 721.221 (.221-AEH) cells, as well as with 721.221 cells incubated with synthetic peptides, which stabilized surface expression of endogenous HLA-E; the response was specifically antagonized by soluble NKG2C- and HLA-E-specific mAbs. By contrast, activation of Jurkat-NKG2C+ was undetectable upon interaction with Human Fetal Foreskin Fibroblasts (HFFF) infected with HCMV laboratory strains (i.e., AD169, Towne), regardless of their differential ability to preserve surface HLA-E expression. On the other hand, infection with two clinical isolates or with the endotheliotropic TB40/E strain triggered Jurkat-NKG2C+ activation; yet, this response was not inhibited by blocking mAbs and was independent of CD94/NKG2C expression. The results are discussed in the framework of previous observations supporting the hypothetical existence of specific ligand(s) for CD94/NKG2C in HCMV-infected cells.

Antibody Cross-Reactivity between Porcine Cytomegalovirus (PCMV) and Human Herpesvirus-6 (HHV-6).

Porcine cytomegalovirus (PCMV) infection is widely prevalent among pigs, and PCMV is one of the viruses which may be transmitted during xenotransplantation using pig cells, tissues, or organs. While human cytomegalovirus (HCMV) is a major risk factor for allotransplantation, it is still unclear whether PCMV is able to infect human cells or pose a risk for xenotransplantation. Previously, it was shown that transmission of PCMV after pig kidney to non-human primate transplantations resulted in a significantly reduced survival time of the transplanted organ. To detect PCMV, PCR-based and immunological methods were used. Screening of pigs by Western blot analyses using recombinant viral proteins revealed up to 100% of the tested animals to be infected. When the same method was applied to screen human sera for PCMV-reactive antibodies, positive Western blot results were obtained in butchers and workers in the meat industry as well as in normal blood donors. To exclude an infection of humans with PCMV, the sera were further investigated. PCMV is closely related to human herpesvirus-6 (HHV-6) and human herpesvirus-7 (HHV-7), and a sequence alignment of glycoprotein B suggests that the antibodies may cross-react with identical epitope sequences. HCMV is not related with PCMV, and no correlation between antibody reactivity against PCMV and HCMV was detected. These data indicate that antibodies against PCMV found in humans are cross-reactive antibodies against HHV-6.