PubMed Health⌕ Search

Biomedical subjects

J Löwer

Publications and source records attributed to J Löwer.

At least 37 records · Page 2Linked to original sources
PubMed1996

Prevalence of hepatitis C virus in plasma pools and the effectiveness of cold ethanol fractionation.

Screening blood donations for antibodies against hepatitis C virus (HCV) greatly reduces the risk of transmitting HCV by transfusions. However, despite such screening programs, plasma pools still contain a high percentage of HCV ribonucleic acid as determined by polymerase chain reaction. This result would not be alarming if the procedures for producing blood products included steps to inactivate or remove HCV. Although this appeared to be the case for all blood products, such as coagulation factors and most immunoglobulins, which are subjected to an inactivation step, the effectiveness of the cold ethanol fractionation process still needed to be determined. In validation experiments using bovine viral diarrhea virus as a model virus for HCV, we demonstrated that the Cohn-Oncley cold ethanol fractionation process neither inactivated nor removed this virus sufficiently. Our observations may help to explain how HCV was transmitted to a number of recipients of intravenous immunoglobulin.

Chemical Fractionation↗
PubMed1996

HERV-K: the biologically most active human endogenous retrovirus family.

The human genome contains a wide variety of endogenous retrovirus-like sequences. The human endogenous retrovirus type K (HERV-K) family comprises 30-50 members per haploid genome in humans and is highly conserved in Old World monkeys and apes. Some proviruses are displaying open reading frames (ORF) with coding capacity for viral particles. HERV-K sequences most likely code for the previously described human teratocarcinoma-derived virus (HTDV) and correlated expression of HERV-K Gag has been demonstrated by immunoelectron microscopy studies. Protease, but not yet reverse transcriptase (RT), enzymatic activity was demonstrated for recombinant HERV-K proteins. However, an ultrasensitive RT assay revealed specific polymerase activity associated with the HTDV particles. HERV-K transcription is specifically regulated by viral long terminal repeats and RNA is expressed at low steady-state levels in a variety of human tissues and tumours. In teratocarcinoma cell lines, HERV-K is highly expressed in a complex pattern showing full-length as well as subgenomic envelope (env) and two alternatively spliced small transcripts. The doubly spliced 1.8-kb mRNA codes for cORF protein which resembles Rev of HIV-1 and is located in the nucleolus. In addition, the cORF sequence acts as a leader and is essential for effective expression of glycosylated HERV-K Env protein. Although HERV-K sequences code for all necessary retroviral proteins, infectious particles could not yet be demonstrated. The putative implication of HERV sequences in pathophysiological processes, for example, testicular malignancies, remains to be elucidated.

Animals↗
PubMed1995

Comparison of 24 different adjuvants for inactivated HIV-2 split whole virus as antigen in mice. Induction of titres of binding antibodies and toxicity of the formulations.

The objective of this study was the comparison of the quantity and quality of the humoral immune response against inactivated whole human immunodeficiency virus type 2. Twenty-four different adjuvants were tested. The toxicity of these preparations was determined. Due to the large number of experiments, the animal model used was the NMRI mouse. Sera were assayed for the presence of antibodies by ELISA and Western blot. The toxicity of the adjuvants was determined by observing lethal side-effects occurring within two days after injection of the immunogenic preparations. The results show that polymethylmethacrylate nanoprticles were the best overall adjuvant, inducing the highest titres of antibodies compared with other adjuvants as well as producing a significantly better immune response against a number of individual HIV-2 antigens without any observable toxic side-effects. However, this adjuvant did not induce antibodies against the outer envelope protein gp120, whereas such antibodies were induced by aluminium compounds, Freund's complete and incomplete adjuvants, and fumed silica (Aerosil). This result suggests the necessity of using vaccines with two or more different adjuvants in order to induce the required immune response against physically different antigens.

AIDS Vaccines↗
PubMed1995

Identification of a Rev-related protein by analysis of spliced transcripts of the human endogenous retroviruses HTDV/HERV-K.

The human endogenous retrovirus family HTDV/HERV-K codes for the viral particles observed in teratocarcinoma cell lines. Two types of proviral genomes exist; these differ in the presence or absence of a stretch of 292 nucleotides. This sequence comprises the amino-terminal part of the env gene, the putative signal peptide, which overlaps in part with the carboxy terminus of the pol gene. Type 2 genomes containing this sequence presumably more closely reflect the structure of the infectious, replication-competent retrovirus ancestors of the HERV-K family than do type 1 genomes that lack the sequence. In human teratocarcinoma cell lines, both variants are expressed. Type 1 genomes, in which pol and env genes are fused, are deficient in splicing. Type 2 transcripts are spliced to subgenomic env mRNA and smaller messages. A doubly spliced transcript encodes a short open reading frame, preliminarily designated cORF (R. Löwer, K. Boller, B. Hasenmeier, C. Korbmacher, N. Mueller-Lantzsch, J. Löwer, and R. Kurth, Proc. Natl. Acad. Sci. USA 90:4480-4484). The genomic organization of cORF resembles that of nonprimate lentivirus rev genes: the first exon comprises nearly the entire signal peptide of env, and the second exon is derived from a different reading frame in the 3' part of the genome. A nucleolar localization signal, which is also a putative RNA binding domain, as well as a sequence with similarities to the Rev effector domain consensus sequence is present in the first exon. Secondary structure analysis reveals similarities to basic helix-loop-helix proteins. cORF is a small protein with an apparent molecular mass of 14 kDa which accumulates in the nucleolus as has been described for Rev proteins.

Amino Acid Sequence↗
PubMed1994

Hepatitis C virus antibody prevalence among human immunodeficiency virus-1-infected individuals: analysis with different test systems.

Sera of 383 human immunodeficiency virus (HIV)-1-infected individuals from Frankfurt (Main)/Germany were assayed by two hepatitis C virus (HCV) screening tests (Abbott second generation, Ortho second generation). This population showed a prevalence for reactivity with both tests of 20.8% (80/383). Examination of all reactive sera (91/383) by a supplemental assay (Chiron RIBA 2) gave for 46 sera a positive, for 33 sera an indeterminate, and for 12 sera a negative result. Further analysis focussed on these RIBA 2-indeterminate and -negative samples. Analysis of the sera using an in-house Western blot with three different Escherichia coli-expressed HCV proteins revealed that none of the RIBA 2-negative, but 24 of the 33 RIBA 2-indeterminate sera, including 3 of 4 c33c (NS3)-reactive samples, were reactive with a recombinant core protein. Twenty-one of 22 c22-3 (core) indeterminates stained the core antigen in the in-house Western blot and 3 of them in addition a NS5 moiety. HCV-polymerase chain reaction (PCR) was positive for 14 of the 24 RIBA 2-indeterminate sera, but for none of the RIBA 2-negative or Western blot nonreactive samples. Discrepant results between the two screening tests could not be explained by differences in the antigen compositions (i.e., a NS3-NS4 moiety of 111 amino acids present in the Ortho enzyme-linked immunosorbent assay (ELISA), not present in the Abbott or RIBA 2 assays).

Acquired Immunodeficiency Syndrome↗
PubMed1993

Identification of human endogenous retroviruses with complex mRNA expression and particle formation.

Retroviruses comprise strains with considerable disease potential in animals and humans. In addition to exogenous strains transmitted horizontally, endogenous proviruses are transmitted through the germ line. Some of these endogenous retroviruses can be pathogenic in mice and possibly in other animal species. They may also be considered as mobile genetic elements with the potential to produce mutations. In humans, genomic DNA contains numerous endogenous retroviral sequences detected by their partial relatedness to animal retroviruses. However, all proviruses sequenced so far have been found to be defective. In this communication, we describe the expression of a family of human endogenous retrovirus sequences (HERV-K) in GH cells, a teratocarcinoma cell line producing the human teratocarcinoma-derived retrovirus (HTDV) particles previously described by us. Four viral mRNA species could be identified, including a full-length mRNA. The other three subgenomic mRNAs are generated by single or double splicing events. This expression pattern is reminiscent of the more complex control of virus gene regulation observed, for example, with lenti- or spumavirus strains, although HERV-K shows no sequence homology to human T-lymphotropic virus or human immunodeficiency virus. Sequence analysis of expressed HERV-K genomes revealed non-defective gag genes, a prerequisite for particle formation. Open reading frames were also observed in pol and env. Antisera raised against recombinant gag proteins of HERV-K stained HTDV particles in immunoelectron microscopy, linking them to the HERV-K family.

Base Sequence↗
PubMed1993

Insufficient inactivation of HIV-1 in human cryo poor plasma by beta-propiolactone: results from a highly accurate virus detection method.

Human cryo poor plasma was spiked with high titre HIV-1 and subjected to a beta-propiolactone (beta-PL) inactivation procedure. The residual titre of HIV-1 was measured using a sensitive and accurate titration technique based upon the killing of MT-4 cells by HIV and the subsequent inability to incorporate 3H-thymidine. It was found that under these conditions a reduction of only 1 log virus titre was achieved after one hour exposure to beta-PL and of 1.8 logs after 5 h. The presence of viable HIV was confirmed using immunohistochemical techniques, by transfer of live virus to fresh cells, and by production of reverse transcriptase. These results have obvious implications for products where human plasma is treated with beta-PL as the only virus inactivation step.

Blood↗
PubMed1993

A general method for the identification of transcribed retrovirus sequences (R-U5 PCR) reveals the expression of the human endogenous retrovirus loci HERV-H and HERV-K in teratocarcinoma cells.

During the past decade, different types of endogenous retroviral sequences have been defined in the human genome usually by low stringency hybridization employing DNA probes of evolutionary conserved animal retrovirus genes. Although all human genomic loci sequenced were found to be defective or interspersed with stop codons, indirect evidence is accumulating that human endogenous retroviral loci are expressed at least in some instances. One example is the synthesis of retroviral particles in human teratocarcinoma cell lines observed by electron microscopy. To establish a link between virus expression and genomic loci we searched for retroviral RNA in human cellular mRNA populations using a generally applicable method. A tRNA-derived primer complementary to a putative retroviral primer binding site was extended by reverse transcription and this product was elongated with a homopolymeric stretch and amplified by PCR (R-U5 PCR). Cloning and sequencing of such products revealed that the endogenous retroviral loci HERV-H and HERV-K are expressed in those human teratocarcinoma cell lines which produce retroviral particles. The size distribution of four HERV-K mRNAs detected in Northern blots is reminiscent of the complex expression pattern seen with a number of exogenous retroviruses.

Animals↗
PubMed1993

Evidence that HERV-K is the endogenous retrovirus sequence that codes for the human teratocarcinoma-derived retrovirus HTDV.

Human teratocarcinoma-derived viruses (HTDV) are retrovirus-like particles that are regularly observed by electron microscopy at low frequency in cell lines established from human teratocarcinomas. Over the last years, one of our teratocarcinoma cell lines spontaneously began to produce high amounts of HTDV. This cell line is stained in immunofluorescence tests by an antiserum raised against recombinant gag protein of HERV-K, an expressed human endogenous retrovirus sequence. In immunoelectron microscopy of ultrathin frozen sections, this anti HERV-Kgag-specific antiserum reacts specifically with HTDV particles. In Western blots, the antiserum recognizes predominantly a protein with an apparent molecular weight of 30 kDa, presumably the major core protein of HTDV particles. Taken together, these results provide evidence that HERV-K codes for HTDV.

Fluorescent Antibody Technique↗
PubMed1991

High antibody titres in mice with polymethylmethacrylate nanoparticles as adjuvant for HIV vaccines.

The aim of the present study was to determine the effect of polymethylmethacrylate (PMMA) nanoparticles as adjuvants for an HIV-2 whole-virus vaccine in mice. The data clearly revealed that PMMA nanoparticles induced 10-100-fold higher antibody titres than aluminium hydroxide or an aqueous vaccine control preparation as measured by enzyme-linked immunosorbent assay. Moreover, the high antibody titres obtained with PMMA as adjuvant appeared to be stable for between 10 and 20 weeks after immunization. In contrast, the titres of the control preparations, fluid or aluminium hydroxide formulations, decreased after 10 weeks.

Adjuvants, Immunologic↗
PubMed1991

Lack of HIV-1 V3 region sequence diversity in two haemophiliac patients infected with a putative biologic clone of HIV-1.

Peripheral blood mononuclear cells (PBMC) from two haemophilia B patients, who presumably became infected with a putative HIV-1 biological clone following treatment with the same suspected batch of commercial factor, were used to clone and sequence the hypervariable V3 region of the HIV-1 envelope protein. In 10 of 12 clones the V3 region was identical and two (one from each patient) had a single non-synonymous point mutation. Viable reisolates (shown to be authentic by sequencing of V3) currently appear to be monocyte tropic. These results strongly indicate that the patients were infected from a common source with a very low number of infectious particles and indicate that variability under these conditions is limited.

Amino Acid Sequence↗