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A Meyerhans

Publications and source records attributed to A Meyerhans.

At least 19 recordsLinked to original sources
PubMed2001

Levels of virus-specific CD4 T cells correlate with cytomegalovirus control and predict virus-induced disease after renal transplantation.

BACKGROUND: Immunosuppressive treatment in transplant patients frequently causes infectious complications with cytomegalovirus (CMV). The extent of CMV replication can be followed by a number of diagnostic methods. There is, however, no simple diagnostic tool to assess the quality of the cellular antiviral immune response of an individual patient. This would be of particular importance for therapy decisions, as patients with detectable virus load do not necessarily develop CMV-related disease. Using a rapid whole blood assay, the frequencies of CMV-reactive CD4 and CD8 T cells were followed after renal transplantation to characterize their relative contribution in the containment of CMV infection. METHODS: T cells from transplant patients ands healthy control persons were stimulated with CMV antigen in vitro. Based on specific cellular activation and induction of intracellular cytokines, the frequency of CMV-reactive CD4 and CD8 T cells was determined using flow cytometry. Viral load quantified using the "hybrid-capture" assay. RESULTS: The absence of CMV complications in long-term transplant recipients is reflected by stable virus-specific T-cell frequencies, which do not differ from healthy CMV-positive controls. In contrast, during the first months after transplantation, clinical symptoms are preceded by a decrease in CMV-reactive CD4 T-cell frequencies and an increase in CMV load. CONCLUSIONS: The individual immune response and CMV replication are critically balanced and can be characterized by assesing both viral load and antiviral T cells. Our experimental design allows the identification of patients with sufficient, insufficient, or absent T-cell activity and can serve as diagnostic tool to facilitate decisions on antiviral therapy.

Adult↗
PubMed2001

Rapid increase of mucosal CD4 T cells followed by clearance of intestinal cryptosporidiosis in an AIDS patient receiving highly active antiretroviral therapy.

Highly active antiretroviral therapy (HAART) suppresses the replication of human immunodeficiency virus (HIV) and leads to an increase in circulating CD4 T lymphocytes, but its effects on other immune compartments such as the intestinal mucosa are not well understood. We describe a severely immunodeficient HIV-infected patient with intractable watery diarrhea and weight loss caused by infection with Cryptosporidium parvum in whom we studied virologic and immunologic changes in both peripheral blood and the intestinal mucosa after initiating HAART. Mucosal biopsies were performed by rectoscopy before and at several time points after HAART was begun. Nucleic acids were extracted from rectal biopsy specimens and blood samples, and HIV RNA was measured by reverse-transcription polymerase chain reaction. Lymphocytes were isolated from rectal biopsy specimens after mechanical disaggregation, and circulating and mucosal CD4 T cells were determined by flow cytometry. HAART led to clinical recovery and eradication of cryptosporidiosis. In both blood and mucosa, HIV RNA decreased below the limit of detection and CD4 T cells increased. Mucosal CD4 T cells increased much faster and to much higher levels than circulating CD4 T cells. Our findings show a rapid repopulation of the intestinal mucosa with CD4 T cells after initiation of HAART that can effectively restore mucosal immunity, leading to eradication of opportunistic pathogens.

Acquired Immunodeficiency Syndrome↗
PubMed2000

Rapid whole blood analysis of virus-specific CD4 and CD8 T cell responses in persistent HIV infection.

OBJECTIVES: Upon HIV infection, strong antiviral cytotoxic and helper T cell responses are generated. They are considered to be an important component in the control of HIV viral load. A simple and rapid whole blood assay was established to quantify and simultaneously characterize HIV-reactive CD4 and CD8 cells. The assay was applied to evaluate the effect of antiretroviral therapy on HIV-specific T cell responses. METHODS: Whole blood of 33 HIV-infected individuals was specifically stimulated by HIV-1 Pr55gag, and activation-induced intracellular cytokine expression in CD4 and CD8 T cells was analysed by flow cytometry. RESULTS: HIV-1-specific CD8 and CD4 T cells can be quantified simultaneously. As specific antigen, HIV-1 Pr55gag virus-like particles were superior to soluble protein, especially for the activation of CD8 T cells. In untreated individuals, a high frequency of HIV-specific T cells was observed. The frequency of CD8 T cells was consistently higher than the respective CD4 T cell response, thus demonstrating a dominance in CD8 T cell expansion in persistent HIV infection. Patients on antiretroviral therapy showed a significant reduction in HIV-specific CD4 and, even more strikingly, CD8 T cells. CONCLUSION: The whole blood assay provides a rapid estimate of the total antiviral T cell resources, and is highly suited for a clinical setting. It may thus have widespread applications for the evaluation of vaccination strategies and immunotherapy. Because antiretroviral therapy significantly reduces both HIV-specific cytotoxic and helper T cell responses, future therapeutic strategies should aim at improving cellular antiviral immunity.

Adult↗
PubMed2000

Kinetics of CXCR4 and CCR5 up-regulation and human immunodeficiency virus expansion after antigenic stimulation of primary CD4(+) T lymphocytes.

The chemokine receptors CCR5 and CXCR4 are coreceptors for the human immunodeficiency virus (HIV) and determine the cell tropism of different HIV strains. Previous studies on their regulation were performed under conditions of unspecific T-lymphocyte stimulation and provided conflicting results. To mimic physiologic conditions, highly purified primary Staphylococcus enterotoxin B (SEB)-reactive CD4 T lymphocytes were stimulated in the presence of autologous antigen-presenting cells and the kinetics of CCR5 and CXCR4 surface expression and HIV replication were studied. Both chemokine receptors were transiently up-regulated with maximal expression at day 3 after stimulation. The stimulated T cells were equally susceptible to productive infection with R5-and X4-tropic virus strains. Thus, antigenic stimulation of T cells promotes efficient replication of both, T cell-tropic and macrophage-tropic HIV. (Blood. 2000;96:1853-1856)

CD4-Positive T-Lymphocytes↗
PubMed2000

Cytotoxic T lymphocyte epitopes of HIV-1 Nef: Generation of multiple definitive major histocompatibility complex class I ligands by proteasomes.

Although a pivotal role of proteasomes in the proteolytic generation of epitopes for major histocompatibility complex (MHC) class I presentation is undisputed, their precise function is currently the subject of an active debate: do proteasomes generate many epitopes in definitive form, or do they merely generate the COOH termini, whereas the definitive NH(2) termini are cleaved by aminopeptidases? We determined five naturally processed MHC class I ligands derived from HIV-1 Nef. Unexpectedly, the five ligands correspond to only three cytotoxic T lymphocyte (CTL) epitopes, two of which occur in two COOH-terminal length variants. Parallel analyses of proteasomal digests of a Nef fragment encompassing the epitopes revealed that all five ligands are direct products of proteasomes. Moreover, in four of the five ligands, the NH(2) termini correspond to major proteasome cleavage sites, and putative NH(2)-terminally extended precursor fragments were detected for only one of the five ligands. All ligands are transported by the transporter associated with antigen processing (TAP). The combined results from these five ligands provide strong evidence that many definitive MHC class I ligands are precisely cleaved at both ends by proteasomes. Additional evidence supporting this conclusion is discussed, along with contrasting results of others who propose a strong role for NH(2)-terminal trimming with direct proteasomal epitope generation being a rare event.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1999

Gamma interferon is a major suppressive factor produced by activated human peripheral blood lymphocytes that is able to inhibit foamy virus-induced cytopathic effects.

The activation of human peripheral blood lymphocytes by mitogens or by triggering the T-cell receptor with anti-CD3 antibodies leads to the production of a potent soluble inhibitory activity against foamy virus-induced cytopathic effects in vitro. The inhibitory activity acts in a species-specific manner. As a consequence, the isolation of foamy viruses from blood lymphocytes of infected humans is accelerated in a heterologous coculture system. Antibodies against gamma interferon (IFN-gamma) are able to suppress most of the inhibitory activity, suggesting that IFN-gamma is the dominant component.

3T3 Cells↗
PubMed1998

Cloning and expression pattern of a murine semaphorin homologous to H-sema IV.

The semaphorin/collapsin family of proteins comprises molecules thought to be important for the guidance of growing axons. All members of this family, which includes both secreted and cell-surface molecules, share a conserved domain of approximately 500 amino acids. Here, we report the cloning of a novel murine semaphorin, termed M-sema IV. It displays 96.3% identity to the human semaphorin H-sema IV and is therefore likely to be the respective murine homologue. In addition, an isoform was identified, which contains an additional 31 amino acids in the semaphorin domain. M-sema IV appears to be expressed ubiquitously in adulthood. During embryogenesis, in situ hybridization revealed M-sema IV expression in subregions of the central nervous system and various other tissues like skin, kidney, lung and intestine.

Amino Acid Sequence↗
PubMed1998

On the role of the second coding exon of the HIV-1 Tat protein in virus replication and MHC class I downregulation.

Tat is an essential protein of human immunodeficiency virus type 1 (HIV-1) and activates transcription from the viral long terminal repeat (LTR) promoter. The tat gene is composed of two coding exons of which the first, corresponding to the N-terminal 72 amino acid residues, has been reported to be sufficient for its transcription function. We introduced a stop codon at the end of the first Tat-coding exon in an expression vector that produces a truncated 71-amino acid Tat protein. This Q72stop mutant displays reduced transcriptional activity of approximately 54% in transient LTR-CAT transfection assays. To test the contribution of the second Tat-coding exon to virus replication, the Q72stop mutation was also introduced in the infectious pLAI molecular clone. The effect on virus replication was analyzed in primary cells and in a transformed T cell line. The fitness of the mutant virus was calculated to be approximately 75% compared with the wild-type control. Thus, a small contribution of the C-terminal Tat domain to viral fitness was measured. It has been proposed that the second Tat-coding exon is involved in transcriptional downregulation of the MHC class I gene of the infected host cell. Cell surface expression of the MHC protein was analyzed in T cells infected with the wild-type LAI virus and the replication-competent Q72stop mutant. MHC expression was transiently reduced on infection with either virus, indicating that the second Tat-coding exon is not involved in this downregulation.

Animals↗
PubMed1998

Herpesvirus saimiri-transformed human CD4+ T-cell lines: an efficient target cell system for the analysis of human immunodeficiency virus-specific cytotoxic CD8+ T-lymphocyte activity.

Herpesvirus saimiri growth-transformed human CD4+ T lymphocytes were examined for their suitability as a target cell system for investigating human immunodeficiency virus (HIV)-specific HLA class I-restricted cytotoxic T-cell activity. Besides CD4, they express the chemokine receptors CCR5 and CXCR4, the common coreceptors of HIV. They are infectible by a range of HIV strains, including primary isolates, becoming efficient targets for CD8-positive HIV-specific cytotoxic T lymphocytes.

Antigens, Viral↗
PubMed1997

Naturally occurring hepatitis B virus genomes bearing the hallmarks of retroviral G-->A hypermutation.

Two hypermutated genomes of hepatitis B virus (HBV) were cloned from sera of chronic virus carriers. Twelve percent and 26% of guanosine residues were replaced by adenosine, with the transitions being erratically distributed along the genome. G-->A substitutions showed a strong dinucleotide preference, decreasing in the order GpA > GpG > > GpC > or = GpT. Such traits are typical of retroviral G-->A hypermutation which results from cDNA synthesis coinciding with fluctuations in the intracellular [dTTP]/[dCTP] ratio. The observations offer an explanation for the high prevalence of HBV variants bearing a tryptophan 28-->stop codon in the pre-core region of carriers with chronic active or fulminant hepatitis. The HBV hypermutants indicate that a small proportion of hepatocytes have distorted dNTP pools, which might have implications for the fidelity of hepatocyte DNA replication or repair.

Adenine↗
PubMed1997

HIV genetic variation is directed and restricted by DNA precursor availability.

The effects of deoxynucleoside triphosphate (dNTP) imbalances on the fidelity of human immunodeficiency virus type 1 (HIV-1) replication were investigated. Using detergent permeabilized virions and biased dNTP concentrations different types of hypermutants were readily produced. However, the mutant spectrum was different from naturally occurring hypermutants demonstrating that the host cell may restrict variation. Using a genetic screen based on the blue/white beta-galactosidase complementation assay, G --> A hypermutants were recovered from HIV-infected thymidine treated U937 cells. Furthermore, hypermutants were recovered from 1 to 2% of resting or activated peripheral blood mononuclear cells indicating that small proportions of primary cells had distorted intracellular [dTTP] and [dCTP]. Such imbalances may underlie a proportion of somatic and germline point mutations and shape to some extent the evolution of mammalian and viral genomes.

Base Sequence↗
PubMed1997

Monocyte-derived dendritic cells represent a transient stage of differentiation in the myeloid lineage.

Cultivation of human peripheral blood monocytes with granulocyte/macrophage colony stimulating factor (GM-CSF) and IL-4 facilitates generation of strongly antigen-presenting dendritic cells (DC). These monocyte-derived DC (mdDC) were used here to further delineate differentiation pathways in the myeloid lineage. Incubation of mdDC with TNF or soluble CD40L led to enhanced MHC and accessory surface antigen expression with significantly elevated T cell stimulatory activity, indicative of DC maturation. In contrast, after cytokine withdrawal or incubation with M-CSF, mdDC differentiated to macrophages. Cells became adherent, monocyte/macrophage surface markers were upregulated, and MHC and accessory surface proteins were downregulated. Furthermore, the multilaminar MHC class II compartments (MIIC) were lost and the T cell stimulating capacity largely diminished. Thus, mdDC show a high developmental plasticity by retaining their ability to become macrophages or to continue their differentiation towards mature DC.

Antigen Presentation↗
PubMed1997

No reactivation of attenuated immunodeficiency viruses in rhesus macaques after vaccinia virus-induced immune activation.

Live-attenuated simian immunodeficiency virus (SIV) protects macaques against challenge with pathogenic SIV. To evaluate the safety of such vaccines, an investigation of whether or not nef-deleted SIV could be reactivated in vivo by immune activation of the host was conducted. In addition, monkeys infected with apathogenic SIV/HIV-1 chimeric viruses, and two control monkeys that had suppressed replication of pathogenic SIV were examined. During the infection virus became undetectable or persisted at a low level of replication in all monkeys. At this time-point 11 monkeys were immune-activated by a vaccinia virus (VV) superinfection. After VV infection up to 80% of their lymphocytes showed expression of the activation markers CD25 and CD69 over 2 weeks. However, only the two non-progressing monkeys infected with pathogenic SIV showed a noticeable but transient enhancement of SIV replication and increased SIV antibody titres. By contrast, in monkeys infected with apathogenic immunodeficiency viruses no change in virus load was observed. Therefore, attenuated immunodeficiency viruses cannot be reactivated in vivo by a VV-induced immune activation.

Animals↗
PubMed1997

Genetic drift can dominate short-term human immunodeficiency virus type 1 nef quasispecies evolution in vivo.

The evolution of human immunodeficiency virus (HIV) type 1 nef quasispecies in a patient clonally infected with a contaminated batch of blood clotting factor IX was monitored. nef sequences were derived at 11, 25, and 41 months postinfection from infected peripheral blood mononuclear cells after molecular cloning of PCR-amplified proviral DNA. The phylogenetic relationships among a total of 41 informative sequences were established by split decomposition analysis and used as a basis to establish a substitution matrix and to score synonymous (s) and nonsynonymous (ns) substitutions. The number of observed in-phase stop codons within the nef sequences was comparable to that expected on a random basis. Similarly, the numbers of observed s and ns substitutions did not differ significantly from expected values. No codon position was preferentially mutated. The maximum sequence divergence increased in a linear manner, with approximately 4.4 nucleotide and approximately 3.2 amino acid changes per year. It appears that stochastic processes strongly influence short-term HIV nef quasispecies evolution in vivo.

Amino Acid Sequence↗