Biomedical subjects

Hartmut Hengel

Publications and source records attributed to Hartmut Hengel.

At least 19 recordsLinked to original sources

PubMed2006

The herpesviral Fc receptor fcr-1 down-regulates the NKG2D ligands MULT-1 and H60.

Members of the alpha- and beta-subfamily of herpesviridae encode glycoproteins that specifically bind to the Fc part of immunoglobulin (Ig)G. Plasma membrane resident herpesviral Fc receptors seem to prevent virus-specific IgG from activating antibody-dependent effector functions. We show that the mouse cytomegalovirus (MCMV) molecule fcr-1 promotes a rapid down-regulation of NKG2D ligands murine UL16-binding protein like transcript (MULT)-1 and H60 from the cell surface. Deletion of the m138/fcr-1 gene from the MCMV genome attenuates viral replication to natural killer (NK) cell response in an NKG2D-dependent manner in vivo. A distinct N-terminal module within the fcr-1 ectodomain in conjunction with the fcr-1 transmembrane domain was required to dispose MULT-1 to degradation in lysosomes. In contrast, down-modulation of H60 required the complete fcr-1 ectodomain, implying independent modes of fcr-1 interaction with the NKG2D ligands. The results establish a novel viral strategy for down-modulating NK cell responses and highlight the impressive diversity of Fc receptor functions.

Animals↗

PubMed2006

The human cytomegalovirus glycoprotein UL16 traffics through the plasma membrane and the nuclear envelope.

The human cytomegalovirus (HCMV) UL16 gene encodes a glycoprotein that interferes with the immune response to the virus-infected cell. In vitro, UL16 interacts with MICB and ULBPs that are ligands for the stimulatory receptor NKG2D, expressed on NK cells and CD8(+)T cells. UL16 expression has been shown to promote intracellular accumulation of MICB, ULBP1 and 2 and thus, interfere with the immune response to HCMV-infected cells. The mechanism that has been suggested for UL16-mediated MICB downmodulation is retention in the ER. Here, we studied the intracellular localization and maturation of UL16 and MICB in HCMV-infected cells and transfectant systems. UL16 trafficked through the ER, TGN and progressed to the plasma membrane, after which the protein was internalized. Strikingly, UL16 was also observed in the inner nuclear membrane. MICB was also localized in the TGN in HCMV-infected cells. These data suggest that MICB trafficking might be affected after its transit through the ER.

Cell Line↗

PubMed2005

Expansion of CD94/NKG2C+ NK cells in response to human cytomegalovirus-infected fibroblasts.

CD94/NKG2C(+) natural killer (NK) cells are increased in healthy individuals infected with human cytomegalovirus (HCMV), suggesting that HCMV infection may shape the NK cell receptor repertoire. To address this question, we analyzed the distribution of NK cell subsets in peripheral blood lymphocytes (PBLs) cocultured with HCMV-infected fibroblasts. A substantial increase of NK cells was detected by day 10 in samples from a group of HCMV(+) donors, and CD94/NKG2C(+) cells outnumbered the CD94/NKG2A(+) subset. Fibroblast infection was required to induce the preferential expansion of CD94/NKG2C(+) NK cells that was comparable with allogeneic or autologous fibroblasts, and different virus strains. A CD94-specific monoclonal antibody (mAb) abrogated the effect, supporting an involvement of the lectinlike receptor. Purified CD56(+) populations stimulated with HCMV-infected cells did not proliferate, but the expansion of the CD94/NKG2C(+) subset was detected in the presence of interleukin-15 (IL-15). Experiments with HCMV deletion mutants indicated that the response of CD94/NKG2C(+) NK cells was independent of the UL16, UL18, and UL40 HCMV genes, but was impaired when cells were infected with a mutant lacking the US2-11 gene region. Taken together the data support that the interaction of CD94/NKG2C with HCMV-infected fibroblasts, concomitant to the inhibition of human leukocyte antigen (HLA) class I expression, promotes an outgrowth of CD94/NKG2C(+) NK cells.

Adult↗

PubMed2005

Physical and functional interactions of the cytomegalovirus US6 glycoprotein with the transporter associated with antigen processing.

The endoplasmic reticulum-resident human cytomegalovirus glycoprotein US6 (gpUS6) inhibits peptide translocation by the transporter associated with antigen processing (TAP) to prevent loading of major histocompatibility complex class I molecules and antigen presentation to CD8+ T cells. TAP is formed by two subunits, TAP1 and TAP2, each containing one multispanning transmembrane domain (TMD) and a cytosolic nucleotide binding domain. Here we reported that the blockade of TAP by gpUS6 is species-restricted, i.e. gpUS6 inhibits human TAP but not rat TAP. Co-expression of human and rat subunits of TAP demonstrates independent binding of gpUS6 to human TAP1 and TAP2, whereas gpUS6 does not bind to rat TAP subunits. gpUS6 associates with preformed TAP1/2 heterodimers but not with unassembled TAP subunits. To locate domains of TAP required for gpUS6 binding and function, we took advantage of reciprocal human/rat intrachain TAP chimeras. Each TAP subunit forms two contact sites within its TMD interacting with gpUS6. The dominant gpUS6-binding site on TAP2 maps to an N-terminal loop, whereas inhibition of peptide transport is mediated by a C-terminal loop of the TMD. For TAP1, two gpUS6 binding domains are formed by loops of the C-terminal TMD. The domain required for TAP inactivation is built by a distal loop of the C-terminal TMD, indicating a topology of TAP1 comprising 10 endoplasmic reticulum transmembrane segments. By forming multimeric complexes, gpUS6 reaches the distant target domains to arrest peptide transport. The data revealed a nonanalogous multipolar bridging of the TAP TMDs by gpUS6.

ATP-Binding Cassette Transporters↗

PubMed2005

A cytomegaloviral protein reveals a dual role for STAT2 in IFN-{gamma} signaling and antiviral responses.

A mouse cytomegalovirus (MCMV) gene conferring interferon (IFN) resistance was identified. This gene, M27, encodes a 79-kD protein that selectively binds and down-regulates for signal transducer and activator of transcription (STAT)-2, but it has no effect on STAT1 activation and signaling. The absence of pM27 conferred MCMV susceptibility to type I IFNs (alpha/beta), but it had a much more dramatic effect on type II IFNs (gamma) in vitro and in vivo. A comparative analysis of M27(+) and M27(-) MCMV revealed that the antiviral efficiency of IFN-gamma was partially dependent on the synergistic action of type I IFNs that required STAT2. Moreover, STAT2 was directly activated by IFN-gamma. This effect required IFN receptor expression and was independent of type I IFNs. IFN-gamma induced increasing levels of tyrosine-phosphorylated STAT2 in M27(-) MCMV-infected cells that were essential for the antiviral potency of IFN-gamma. pM27 represents a new strategy for simultaneous evasions from types I and II IFNs, and it documents an unknown biological significance for STAT2 in antiviral IFN-gamma responses.

Animals↗

PubMed2005

NK cell activation through the NKG2D ligand MULT-1 is selectively prevented by the glycoprotein encoded by mouse cytomegalovirus gene m145.

The NK cell-activating receptor NKG2D interacts with three different cellular ligands, all of which are regulated by mouse cytomegalovirus (MCMV). We set out to define the viral gene product regulating murine UL16-binding protein-like transcript (MULT)-1, a newly described NKG2D ligand. We show that MCMV infection strongly induces MULT-1 gene expression, but surface expression of this glycoprotein is nevertheless completely abolished by the virus. Screening a panel of MCMV deletion mutants defined the gene m145 as the viral regulator of MULT-1. The MCMV m145-encoded glycoprotein turned out to be necessary and sufficient to regulate MULT-1 by preventing plasma membrane residence of MULT-1. The importance of MULT-1 in NK cell regulation in vivo was confirmed by the attenuating effect of the m145 deletion that was lifted after NK cell depletion. Our findings underline the significance of escaping MULT-1/NKG2D signaling for viral survival and maintenance.

Animals↗

PubMed2005

Viruses know it all: new insights into IFN networks.

Co-evolution of viruses with their hosts for millions of years has led to a host immune system of high complexity and, likewise, sophisticated viral mechanisms to antagonize immunity. Early cytokines, such as interferons (IFNs), which integrate innate and adaptive immune responses, are essential targets for viruses. Viral antagonists that interfere with numerous components of the IFN system provide superb tools to explore the pathways and the connectivity of the IFN network. Here, the inhibition of type I IFN production by negative strand RNA viruses and IFN signaling by cytomegalovirus are discussed, illustrating unappreciated links between type I and type II IFN signaling. Viral principles might pave the way to develop new therapeutics to modulate immune functions.

Animals↗

PubMed2005

Probing neutralizing-antibody responses against emerging measles viruses (MVs): immune selection of MV by H protein-specific antibodies?

Measles virus (MV) infection and vaccination induce long-lasting immunity and neutralizing-antibody responses that are directed against the MV haemagglutinin (H) and the fusion (F) protein. A new MV genotype, D7, emerged recently in western Germany and rapidly replaced the long-term endemically circulating genotypes C2 and D6. Analysis of the H gene of C2, D6, D7 and vaccine viruses revealed uniform sequences for each genotype. Interestingly, a consistent exchange of seven distinct amino acids in the D7 H was observed when compared with residues shared between C2, D6 and vaccine viruses, and one exchange (D416-->N) in the D7 H was associated with an additional N-linked glycosylation. In contrast, the F gene is highly conserved between MVs of these genotypes. To test whether the D7 H protein escapes from antibody responses that were raised against earlier circulating or vaccine viruses, the neutralizing capacity of mAbs recognizing seven distinct domains on the H of an Edmonston-related MV was compared. The mAbs revealed a selective and complete loss of two neutralizing epitopes on the D7 H when compared with C2, D6 and vaccine viruses. To assess whether these alterations of the D7 H affect the neutralizing capacity of polyclonal B-cell responses, genotype-specific antisera were produced in cotton rats. However, no significant genotype-dependent difference was found. Likewise, human sera obtained from vaccinees (n=7) and convalescents (n=6) did not distinguish between the MV genotypes. Although the hypothesis of selection of D7 viruses by pre-existing neutralizing antibodies is compatible with the differing pattern of neutralizing epitopes on the H protein, it was not confirmed by the results of MV neutralization with polyclonal sera.

Adolescent↗

PubMed2005

Selective down-regulation of the NKG2D ligand H60 by mouse cytomegalovirus m155 glycoprotein.

Both human and mouse cytomegaloviruses (CMVs) encode proteins that inhibit the activation of NK cells by down-regulating cellular ligands for the activating NK cell receptor NKG2D. Up to now, three ligands for the NKG2D receptor, named RAE-1, H60, and MULT-1, have been identified in mice. The resistance of mouse strains to murine CMV (MCMV) infection is determined by their ability to generate an effective NK cell response. The MCMV gene m152, a member of the m145 gene family, down-regulates the expression of RAE-1 in order to avoid NK cell control in vivo. Here we report that the m155 gene, another member of the m145 gene family, encodes a protein that interferes with the expression of H60 on the surfaces of infected cells. Deletion of the m155 gene leads to an only partial restoration of H60 expression on the cell surface, suggesting the involvement of another, so far unknown, viral inhibitor. In spite of this, an m155 deletion mutant virus shows NK cell-dependent attenuation in vivo. The acquisition of endo-beta-N-acetylglucosaminidase H resistance and the preserved half-life of H60 in MCMV-infected cells indicate that the m155-mediated effect must take place in a compartment after H60 exits from the ERGIC-cis-Golgi compartment.

Animals↗

PubMed2004

Herpesviral Fcgamma receptors: culprits attenuating antiviral IgG?

Production of IgG in response to virus infection is central to antiviral immune effector functions and a hallmark of B cell memory. Antiviral antibodies (Abs) recognising viral glycoproteins or protein antigen displayed on the surface of virions or virus-infected cells are crucial in rendering the virus noninfectious and in eliminating viruses or infected cells, either acting alone or in conjunction with complement. In many instances, passive transfer of Abs is sufficient to protect from viral infection. Herpesviruses (HV) are equipped with a large array of immunomodulatory functions which increase the efficiency of infection by dampening the antiviral immunity. Members of the alpha- and beta-subfamily of the Herpesviridae are distinct in encoding transmembrane glycoproteins which selectively bind IgG via its Fc domain. The Fc-binding proteins constitute viral Fcgamma receptors (vFcgammaRs) which are expressed on the cell surface of infected cells. Moreover, vFcgammaRs are abundantly incorporated into the envelope of virions. Despite their molecular and structural heterogeneity, the vFcgammaRs generally interfere with IgG-mediated effector functions like antibody (Ab)-dependent cellular cytolysis, complement activation and neutralisation of infectivity of virions. vFcgammaRs may thus contribute to the limited therapeutic potency of antiherpesviral IgG in clinical settings. A detailed molecular understanding of vFcgammaRs opens up the possibility to design recombinant IgG molecules resisting vFcgammaRs. Engineering IgG with a better antiviral efficiency represents a new therapeutic option against herpesviral diseases.

Animals↗

PubMed2004

Laboratory investigations are indispensable to monitor the progress of measles elimination--results of the German Measles Sentinel 1999-2003.

BACKGROUND: The elimination of measles is a goal set by the World Health Organisation to be reached by 2010 in the European region. OBJECTIVES: To enhance the measles surveillance in Germany, a country-wide laboratory supported a sentinel was established. STUDY DESIGN: A network of >1200 representatively distributed practitioners reported detailed data on all clinically diagnosed cases and provided specimens for laboratory diagnosis. RESULTS: A total of 3225 suspected cases were reported between October 1999 and December 2003. The incidence in Western Germany decreased from >15 cases per 100,000 population to one case in 2003, while in Eastern Germany <1 case per 100,000 population was observed during these years. Laboratory investigations were undertaken in 40% of cases in 2000/2001. This rate increased to 79% in 2003. Simultaneously, the rate of confirmed cases dropped from 60% in the former years to 23% in 2003. Measles virus (MV) detection by serology and by PCR revealed concordant results in 92%. Most suspected cases (85%) were unvaccinated with 66% being laboratory confirmed. Only 10% of suspected cases occurred in vaccinated individuals and very few (22%) could be confirmed. Analyses of confirmed measles in vaccinated patients (n = 49) revealed 24.5% primary vaccine failures, 24.5% reinfections after successful vaccination and 31% MV infection before or shortly after vaccination. The genetic characterisation of 389 MV isolates identified eight genotypes: B3, C2, D4, D5, D6, D7, G2 and H1. Only the C2, D6 and D7 MV genotypes circulated endemically in Western Germany. The newly emerged MV D7 almost completely replaced the pre-existing C2 and D6 MVs in 2001. The few measles cases detected in Eastern Germany were mostly caused by imported MVs. CONCLUSION: The data demonstrate that laboratory investigations including molecular methods are an indispensable tool for surveillance in all countries advanced in measles elimination.

Adolescent↗

PubMed2004

A cytomegalovirus inhibitor of gamma interferon signaling controls immunoproteasome induction.

Both human and mouse cytomegaloviruses (HCMV and MCMV) avoid peptide presentation through the major histocompatibility complex (MHC) class I pathway to CD8(+) T cells. Within the MHC class I pathway, the vast majority of antigenic peptides are generated by the proteasome system, a multicatalytic protease complex consisting of constitutive subunits, three of which can be replaced by enzymatically active gamma interferon (IFN-gamma)-inducible subunits, i.e., LMP2, LMP7, and MECL1, to form the so-called immunoproteasomes. Here, we show that steady-state levels of immunoproteasomes are readily formed in response to MCMV infection in the liver. In contrast, the incorporation of immunoproteasome subunits was prevented in MCMV-infected, as well as HCMV-infected, fibroblasts in vitro. Likewise, the expression of the IFN-gamma-inducible proteasome regulator PA28 alpha beta was also impaired in MCMV-infected cells. Both MCMV and HCMV did not alter the constitutive-subunit composition of proteasomes in infected cells. Quantitative assessment of LMP2, MECL1, and LMP7 transcripts revealed that the inhibition of immunoproteasome formation occurred at a pretranscriptional level. Remarkably, a targeted deletion of the MCMV gene M27, encoding an inhibitor of STAT2 that disrupts IFN-gamma receptor signaling, largely restored transcription and protein expression of immunoproteasome subunits in infected cells. While CMV block peptide transport and MHC class I assembly by posttranslational strategies, immunoproteasome assembly, and thus the repertoire of proteasomal peptides, is controlled by pretranscriptional mechanisms. We hypothesize that the blockade of immunoproteasome formation has considerable consequences for shaping the CD8(+)-T-cell repertoire during the effector phase of the immune response.

Animals↗

PubMed2004

Expansion of protective CD8+ T-cell responses driven by recombinant cytomegaloviruses.

CD8(+) T cells are critical for the control of many persistent viral infections, such as human immunodeficiency virus, hepatitis C virus, Epstein-Barr virus, and cytomegalovirus (CMV). In most infections, large CD8(+)-T-cell populations are induced early but then contract and are maintained thereafter at lower levels. In contrast, CD8(+) T cells specific for murine CMV (MCMV) have been shown to gradually accumulate after resolution of primary infection. This unique behavior is restricted to certain epitopes, including an immunodominant epitope derived from the immediate-early 1 (IE1) gene product. To explore the mechanism behind this further, we measured CD8(+)-T-cell-mediated immunity induced by recombinant MCMV-expressing epitopes derived from influenza A virus or lymphocytic choriomeningitis virus placed under the control of an IE promoter. We observed that virus-specific CD8(+)-T-cell populations were induced and that these expanded gradually over time. Importantly, these CD8(+) T cells provided long-term protection against challenge without boosting. These results demonstrate a unique pattern of accumulating T cells, which provide long-lasting immune protection, that is independent of the initial immunodominance of the epitope and indicates the potential of T-cell-inducing vaccines based on persistent vectors.

Animals↗

PubMed2004

Hepatitis C virus mutation affects proteasomal epitope processing.

The high incidence of hepatitis C virus (HCV) persistence raises the question of how HCV interferes with host immune responses. Studying a single-source HCV outbreak, we identified an HCV mutation that impaired correct carboxyterminal cleavage of an immunodominant HLA-A2-restricted CD8 cell epitope that is frequently recognized by recovered patients. The mutation, a conservative HCV nonstructural protein 3 (NS3) tyrosine to phenylalanine substitution, was absent in 54 clones of the infectious source, but present in 15/21 (71%) HLA-A2-positive and in 11/24 (46%) HLA-A2-negative patients with chronic hepatitis C. In order to analyze whether the mutation affected the processing of the HLA-A2-restricted CD8 cell epitope, mutant and wild-type NS3 polypeptides were digested in vitro with 20S constitutive proteasomes and with immunoproteasomes. The presence of the mutation resulted in impaired carboxyterminal cleavage of the epitope. In order to analyze whether impaired epitope processing affected T cell priming in vivo, HLA-A2-transgenic mice were infected with vaccinia viruses encoding either wild-type or mutant HCV NS3. The mutant induced fewer epitope-specific, IFN-gamma;-producing and fewer tetramer(+) cells than the wild type. These data demonstrate how a conservative mutation in the flanking region of an HCV epitope impairs the induction of epitope-specific CD8(+) T cells and reveal a mechanism that may contribute to viral sequence evolution in infected patients.

Amino Acid Sequence↗

PubMed2003

Memory inflation: continuous accumulation of antiviral CD8+ T cells over time.

CD8+ T lymphocytes play an important role in the control of intracellular pathogens during both acute and persistent infections. This is particularly true in the case of persistent herpesviruses such as human CMV, which are typified by large virus-specific CD8+ T cell populations during viral latency. To understand the origin of these populations and the factors shaping them over time, we investigated the CD8+ T cell response after murine CMV (MCMV) infection. The kinetics of the acute response were characterized by rapid expansion of activated T cells, followed by a contraction phase. Thereafter, we observed a striking pattern, where MCMV-specific memory CD8+ T cells steadily accumulated over time, with 20% of all CD8+ T cells at 1 year specific for one MCMV epitope. Accumulation of MCMV-specific CD8+ T lymphocytes was seen in all organs tested and was associated with continuous activation of specific CD8+ T lymphocytes, primarily within lymph nodes. The pattern of accumulation was observed in only two of five epitopes tested, and was accompanied by a gradual restriction in usage of the variable region of the TCR beta-chain over time. This novel pattern of a virus-specific CD8+ T cell response suggests that continuous or repetitive exposure to Ag can slowly mold memory T cell populations over time. This may be relevant for understanding the evolution of the large human CMV-specific CD8+ T cell populations seen in humans.

Animals↗

PubMed2003

HCMV glycoprotein US6 mediated inhibition of TAP does not affect HLA-E dependent protection of K-562 cells from NK cell lysis.

Human cytomegalovirus has evolved multiple strategies to interfere with immune recognition by the host. A variety of mechanisms affect antigen presentation by major histocompatibility complex class I molecules resulting in a reduced class I cell-surface expression. This downregulation is expected to trigger natural killer (NK) cytotoxicity, requiring counteraction by the virus to establish long-term infection. Here we describe that the human cytomegalovirus gpUS6 protein, which has been demonstrated to downregulate the expression of human leukocyte antigen (HLA) class I and the presentation of cytotoxic T lymphocyte epitopes by blocking transporter associated with antigen presentation (TAP function), does not affect the ability of HLA-E to inhibit NK cell mediated lysis of K-562 cells by interaction with CD94/NKG2A expressed on NK cells. Cell surface expression and function of HLA-E is not altered although gpUS6 inhibits TAP-dependent peptide transport by 95%. Moreover, HLA-E molecules presenting HLA class I signal sequence-derived peptides are functionally detectable on transfected TAP-deficient RMA-S cells.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2003

Combinatorial immunotherapies for infectious diseases.

Combating pathogenic organisms by combinatorial approaches involving appropriate immune response molecules and antimicrobial drugs represents a progessively more apparent and successful therapeutic paradigm for the treatment of acute and chronic persistent infectious diseases. This review explores areas of current innovation and provides an update of the present state of knowledge concerning combination of chemotherapy with several immune-based interventions in infections. In the future, a better understanding of microbial immune modulation and evasion may continue to open new avenues of inquiry and carefully targeted application of adjunctive immunotherapies.

Animals↗

PubMed2002

MCMV glycoprotein gp40 confers virus resistance to CD8+ T cells and NK cells in vivo.

The susceptibility of certain inbred mouse strains to murine cytomegalovirus (MCMV) is related to their inability to generate a strong natural killer (NK) cell response. We addressed here whether the MCMV susceptibility of the BALB/c strain is due to viral functions that control NK cell activation in a strain-specific manner. MCMV expresses two proteins, gp48 and gp40, that are encoded by the genes m06 and m152, respectively; they down-regulate major histocompatibility complex (MHC) class I expression at the plasma membrane. Using MCMV deletion mutants and revertants, we found that gp40 but not gp48 controls NK cell activation. Absence of gp40 improved antiviral NK cell control in BALB/c, but not C57BL/6, mice. Down-regulation of H-60, the high-affinity ligand for the NKG2D receptor, was the mechanism by which gp40 modulates NK cell activation. Thus, a single herpesvirus protein has a dual function in inhibiting both the adaptive as well as the innate immune response.

Animals↗