A sublethal dose of the neonicotinoid insecticide acetamiprid reduces sperm density in a songbird

Farmland bird species are particularly exposed to pesticides through various pathways. Among pesticides, neonicotinoids insecticides are commonly used in agriculture, but their influence on bird reproductive capacities is poorly understood. In this study, we experimentally tested the effects of the neonicotinoid acetamiprid on House sparrows' sperm quality and oxidative status following ingestion of a low and field-realistic dose of the compound. To do so, 56 males were captured, held and orally dosed seven times over 19 days of experiment with either a saline solution (control) or an acetamiprid-saline solution, and sperm samples were retrieved before and after the experiment. The overall dose given to the birds corresponded to 0.5% of the LD₅₀ for the Zebra finch (5.7 mg/kg BW) spread into 7 separate doses and administered every three days over the entire duration of the study (ca. 0.07% LD₅₀ per oral dose). Sperm mobility and sperm oxidative status were unaffected by the treatment, but sperm density was. Birds that received oral doses of acetamiprid suffered a significant decline in their sperm density compared to control birds. This result was confirmed by a significant decrease in the activity of the antioxidant enzyme SOD in the sperm of acetamiprid-dosed birds. These results provide the first evidence of sublethal toxicity of acetamiprid in a songbird and suggest that passerine birds' fertility may be negatively affected by very small doses of neonicotinoids in the wild.

Occurrence of polybrominated diphenyl ethers, perfluorinated compounds, and nonsteroidal anti-inflammatory drugs in freshwater mussels from Latvia

The occurrence of polybrominated diphenyl ethers (PBDE), perfluorinated compounds (PFC), and nonsteroidal anti-inflammatory drugs (NSAID) in Latvian freshwater ecosystems was evaluated by using filter-feeding mussels as bioindicators. Twenty four samples of mussels were collected from freshwater bodies throughout the territory of Latvia during the summer of 2017. PBDE contamination was ubiquitous, reaching the highest total concentration of 193.2 pg g^-1 w.w. BDE-209 was the most abundant compound, followed by penta-BDE components BDE-49, -100, -99, -153, -154, and -47 in decreasing order. The levels of PFCs in Latvian mussels were generally lower than those reported from other regions. Perfluorooctanoic acid (PFOA) was more common in mussels than perfluorooctane sulfonate (PFOS). Ibuprofen was the only NSAID detected in mussels during this study (detection frequency 50%). The observed concentrations of this compound varied between 0.52 and 109 ng g^-1 w.w., being noticeably higher than reported by other authors. Overall, the results indicate that among the three analysed groups of contaminants, ibuprofen is present in Latvian freshwater environment at relatively high levels and further monitoring should be carried out.

Glutamic residue 438 within the protease-sensitive subdomain of HIV-1 reverse transcriptase is critical for heterodimer processing in viral particles

The biological form of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) is a heterodimer consisting of two polypeptides, p66 and p51, which have identical N-termini. The p51 polypeptide is generated by action of viral protease cleaving the p66 polypeptide between residues Phe440 and Tyr441. Dimerization has been mostly studied using bacterially purified RT bearing amino acid changes in either subunit, but not in the context of HIV-1 particles. We introduced changes of conserved amino acid residues 430-438 into the protease-sensitive subdomain of the p66 subunit and analyzed the reverse transcriptase processing and function using purified variants and their corresponding HIV-1 recombinant clones. Our mutational analysis shows that the conserved Glu438 residue is critical for proper heterodimerization and function of virion-associated RT, but not of bacterially expressed RT. In contrast, the conserved Glu430, Glu432, and Pro433 residues are not important for dimerization of virion-associated RT. The network of interactions made by the Glu438 carboxyl group with neighboring residues is critical to protect the Phe440-Tyr441 from cleavage in the context of the p66/p51 heterodimer and may explain why the p66/p51 is not processed further to p51/p51.

An integrated system to study multiply substituted human immunodeficiency virus type 1 reverse transcriptase

We describe a gene system allowing the facile production of multiply substituted reverse transcriptases (RTs), the enzymatic characterization of these purified RTs, and the study of these mutations in the defined genetic background of the macrophagetropic, non-laboratory-adapted human immunodeficiency virus type 1 (HIV-1) AD8 strain. Thirteen unique silent restriction sites were introduced in the pol gene encoding HIV-1 RT, allowing easy introduction of mutations. To simplify genetic manipulation and generate p66/p51 heterodimers in Escherichia coli, a gene construct of the viral protease alone was optimized for expression from a separate vector carrying a p15A origin of replication. Active-site titration experiments using pre-steady-state kinetics showed that our system yields a higher proportion of active enzyme than that obtained by alternate methods. To facilitate phenotype/genotype correlations, the modified RT gene was designed to be easily reintroduced into a recombinant proviral AD8 HIV-1 DNA. Infectious viruses made from this vector were undistinguishable from wild-type AD8 HIV-1, an isolate able to infect peripheral blood mononuclear cells and macrophages. Thus, the pol gene can tolerate many silent mutations in the polymerase domain without affecting the functionality of the HIV-1 genome. The system was validated biochemically and virologically using the V75T substitution associated with stavudine resistance.

The valine-to-threonine 75 substitution in human immunodeficiency virus type 1 reverse transcriptase and its relation with stavudine resistance

The amino acid change V75T in human immunodeficiency virus type 1 reverse transcriptase confers a low level of 2',3'-didehydro-2',3'-dideoxythymidine (stavudine, d4T) resistance in vivo and in vitro. Valine 75 is located at the basis of the fingers subdomain of reverse transcriptase between the template contact point and the nucleotide-binding pocket. V75T reverse transcriptase discriminates 3.6-fold d4T 5'-triphosphate relative to dTTP, as judged by pre-steady state kinetics of incorporation of a single nucleotide into DNA. In addition, V75T increases the DNA polymerization rate up to 5-fold by facilitating translocation along nucleic acid single-stranded templates. V75T also increases the reverse transcriptase-mediated repair of the d4TMP-terminated DNA by pyrophosphate but not by ATP. The V75T/Y146F double substitution partially suppressed both increases in rate of polymerization and pyrophosphorolysis, indicating that the hydroxyl group of Thr-75 interacts with that of Tyr-146. V75T recombinant virus was 3-4-fold d4T-resistant and 3-fold resistant to phosphonoformic acid relative to wild type, confirming that the pyrophosphate traffic is affected in V75T reverse transcriptase. Thus, in addition to nucleotide selectivity V75T defines a type of amino acid change conferring resistance to nucleoside analogues that links translocation rate to the traffic of pyrophosphate at the reverse transcriptase active site.

The HIV-1 Vpr co-activator induces a conformational change in TFIIB

Vpr is a HIV-1 virion-associated protein which plays a role in viral replication and in transcription and cell proliferation. We have previously reported that Vpr stimulates transcription of genes lacking a common DNA target sequence likely through its ability to interact with TFIIB. However, the molecular mechanism of the Vpr-mediated transcription remains to be precisely defined. In this in vitro study, we show that the binding site of Vpr in TFIIB overlaps the domain of TFIIB which is engaged in the intramolecular bridge between the N- and C-terminus of TFIIB, highly suggesting that binding of Vpr may induce a change in the conformation of TFIIB. Indeed, with a partial proteolysis assay using V8 protease, we demonstrate that Vpr has the ability to change the conformation of TFIIB. We investigated in this partial proteolysis assay a series of Vpr-mutated proteins previously defined for their transactivation properties. Our data show a correlation between the ability of Vpr-mutated proteins to stimulate transcription and their ability to induce a conformational change in TFIIB, indicating a functional relevance of the Vpr-TFIIB interaction.

NMR structure of the (52-96) C-terminal domain of the HIV-1 regulatory protein Vpr: molecular insights into its biological functions

The HIV-1 regulatory protein Vpr (96 amino acid residues) is incorporated into the virus particle through a mechanism involving its interaction with the C-terminal portion of Gag. Vpr potentiates virus replication by interrupting cell division in the G2 phase and participates in the nuclear transport of proviral DNA. The domain encompassing the 40 C-terminal residues of Vpr was shown to be involved in cell cycle arrest and binding of nucleocapsid protein NCp7, and suggested to promote nuclear provirus transfer. Accordingly, we show here that the synthetic 52-96 but not 1-51 sequences of Vpr interact with HIV-1 RNA. Based on these results, the structure of (52-96)Vpr was analysed by two-dimensional 1H-NMR in aqueous TFE (30%) solution and refined by restrained molecular dynamics. The structure is characterized by a long (53-78) amphipathic alpha-helix, followed by a less defined (79-96) C-terminal domain. The Leu60 and Leu67 side-chains are located on the hydrophobic side of the helix, suggesting their involvement in Vpr dimerization through a leucine zipper-type mechanism. Accordingly, their replacement by Ala eliminates Vpr dimerization in the two hybrid systems, while mutations of Ile74 and Ile81 have no effect. This was confirmed by gel filtration measurements and circular dichroism, which also showed that the alpha-helix still exists in (52-96)Vpr and its Ala60, Ala67 mutant in the presence and absence of TFE. Based on these results, a model of the coiled-coil Vpr dimer has been described, and its biological relevance as well as that of the structural characteristics of the 52-96 domain for the different functions of Vpr, including HIV-1 RNA binding, are discussed.

DNA repair enzyme uracil DNA glycosylase is specifically incorporated into human immunodeficiency virus type 1 viral particles through a Vpr-independent mechanism

The Vpr protein, encoded by the human immunodeficiency virus type 1 (HIV-1) genome, is one of the nonstructural proteins packaged in large amounts into viral particles. We have previously reported that Vpr associates with the DNA repair enzyme uracil DNA glycosylase (UDG). In this study, we extended these observations by investigating whether UDG is incorporated into virions and whether this incorporation requires the presence of Vpr. Our results, with highly purified viruses, show that UDG is efficiently incorporated either into wild-type virions or into Vpr-deficient HIV-1 virions, indicating that Vpr is not involved in UDG packaging. Using an in vitro protein-protein binding assay, we reveal a direct interaction between the precursor form of UDG and the viral integrase (IN). Finally, we demonstrate that IN-defective viruses fail to incorporate UDG, indicating that IN is required for packaging of UDG into virions.

A role for human immunodeficiency virus type 1 Vpr during infection of peripheral blood mononuclear cells

Studies analysing human immunodeficiency virus type 1 replication in primary cells have demonstrated that Vpr, although dispensable, plays a role along with the matrix (MA) protein in allowing nuclear localization of viral preintegration complexes in non-dividing monocyte-derived macrophages (MDMs). In the current study, experimental infection conditions to analyse the role of Vpr, independently of MA, during infection of PHA/IL-2-stimulated peripheral blood mononuclear cells (PBMC) were designed. It was shown that the absence of Vpr results in a subtle effect on virus production in long-term infection. PCR analysis of the steps of virus retrotranscription during a single cycle of replication in stimulated PBMC revealed that the absence of Vpr alone correlates with an impairment in the nuclear localization of viral DNA. Our data indicate that Vpr is involved in the virus life-cycle during infection of dividing PBMC, presumably as it is during infection of MDMs.

Diversity of HIV-1 Vpr interactions involves usage of the WXXF motif of host cell proteins

Targeting protein or RNA moieties to specific cellular compartments may enhance their desired functions and specificities. Human immunodeficiency virus type I (HIV-1) encodes proteins in addition to Gag, Pol, and Env that are packaged into virus particles. One such retroviral-incorporated protein is Vpr, which is present in all primate lentiviruses. Vpr has been implicated in different roles within the HIV-1 life cycle. In testing a new hypothesis in which viral proteins are utilized as docking sites to incorporate protein moieties into virions, we used the peptide phage display approach to search for Vpr-specific binding peptides. In the present studies, we demonstrate that most of the peptides that bind to Vpr have a common motif, WXXF. More importantly, we demonstrate that the WXXF motif of uracil DNA glycosylase is implicated in the interaction of uracil DNA glycosylase with Vpr intracellularly. Finally, a dimer of the WXXF motif was fused to the chloramphenicol acetyl transferase (CAT) gene, and it was demonstrated that the WXXF dimer-CAT fusion protein construct produces CAT activity within virions in the presence of Vpr as a docking protein. This study provides a novel potential strategy in the targeting of anti-viral agents to interfere with HIV-1 replication.

Secretion of extracellular factor(s) induced by X-irradiation activates the HIV type 1 long terminal repeat through its kappaB motif

X-irradiation has been used in the treatment of several human diseases, including AIDS-related-malignancies. X-irradiation might induce the transcription and the replication of human immunodeficiency virus type 1 (HIV-1) and enhance nuclear factor kappa B (NF-kappaB). In the present article we show that the activation of the HIV-1 long terminal repeat (LTR) by direct X-irradiation can be mimicked by coculture of transfected cells with X-irradiated nontransfected (HIV-1-negative) cells. In the human colonic carcinoma cell line HT29, the activation seems to depend on an extracellular factor(s) released by a cell line treated with X-rays. The HIV-1 LTR cis-acting element conferring X-indirect responsiveness was identified as the kappaB tandem motif. The two main nuclear HIV-1 kappaB-binding complexes activated by X-direct and -indirect irradiation were the NF-kappaB p50/p65 and c-Rel/p65 heterodimers. Nuclear NF-kappaB activation was dependent on protein neosynthesis. It was partially inhibited by 100 microM pyrrolidine dithiocarbamate, a potent antioxidant drug, but was not correlated with a significant decrease in cellular IkappaBalpha. Furthermore, X-irradiation induces the expression of several cytokine genes generally associated with stress response and antibodies against interleukin 6 and TNF-alpha partially inhibited the X-indirect activation of the HIV-1 LTR. The use of protein kinase C (PKC)-specific inhibitor and of forskolin, an adenylate cyclase activator, suggests that a PKC-dependent pathway and the cAMP intracellular concentration could play a role in the X-indirect enhancement of HIV-1 LTR transcription in the HT29 cell line. In addition, supernatants of an X-irradiated HT29 cell culture activated the HIV-1 stimulation in infected peripheral blood monocytes.

Human immunodeficiency virus type 1 Vif protein binds to the Pr55Gag precursor

The Vif protein of human immunodeficiency virus type 1 is required for productive replication in peripheral blood lymphocytes. Previous reports suggest that vif-deleted viruses are limited in replication because of a defect in the late steps of the virus life cycle. One of the remaining questions is to determine whether the functional role of Vif involves a specific interaction with virus core proteins. In this study, we demonstrate a direct interaction between Vif and the Pr55Gag precursor in vitro as well as in infected cells. No interaction is observed between Vif and the mature capsid protein. The Pr55Gag-Vif interaction is detected (i) in the glutathione S-transferase system, with in vitro-translated proteins demonstrating a critical role of the NC p7 domain of the Gag precursor; (ii) with proteins expressed in infected cells; and (iii) by coimmunoprecipitation experiments. Deletion of the C-terminal 22 amino acids of Vif abolishes its interaction with the Pr55Gag precursor. Furthermore, point mutations in the C-terminal domain of Vif which have been previously shown to abolish virus infectivity and binding to cell membranes dramatically decrease the Gag-Vif interaction. These results suggest that the interaction between Vif and the pr55Gag precursor is a critical determinant of Vif function.

Uracil DNA glycosylase specifically interacts with Vpr of both human immunodeficiency virus type 1 and simian immunodeficiency virus of sooty mangabeys, but binding does not correlate with cell cycle arrest

The Vpr protein encoded by human immunodeficiency virus type 1 (HIV-1) is important for growth of virus in macrophages and prevents infected cells from passing into mitosis (G2 arrest). The cellular target for these functions is not known, but Vpr of HIV-1 and the related Vpr from simian immunodeficiency virus of sooty mangabeys (SIV(SM)) bind the DNA repair enzyme UNG, while the Vpx protein of SIV(SM) does not. Nonetheless, a mutational analysis of Vpr showed that binding to UNG is neither necessary nor sufficient for the effect of Vpr on the cell cycle.

Phenotypically Vif- human immunodeficiency virus type 1 is produced by chronically infected restrictive cells

The permissivity of CD4+ transformed T cells for the replication of human immunodeficiency virus type 1 (HIV-1) vif mutants varies widely between different cell lines. Mutant vif-negative viruses propagate normally in permissive CD4+ cell lines but are unable to establish a productive infection in restrictive cell lines such as H9. As a consequence, elucidation of the function of Vif has been considerably hampered by the inherent difficulty in obtaining a stable source of authentically replication-defective vif-negative viral particles produced by restrictive cells. vif-negative, vpr-negative HIV-1 strain NDK stock, produced by the permissive SupT1 cell line, was used to infect restrictive H9 cells. By using a high multiplicity, infection of H9 cells was achieved, leading to persistent production of viral particles displaying a dramatically reduced infectious virus titer when measured in a single-cycle infectivity assay. Although these viral particles were unable to further propagate in H9 cells, they could replicate normally in CEM and SupT1 cells. Comparison of unprocessed and processed Gag proteins in the persistently produced vif-negative viral particles revealed no defect in the processing of polypeptide precursors, with no inversion of the Pr55gag/p24 ratio. In addition, there was no defect in Env incorporation for the vif-negative viral particles. Despite their apparently normal protein content, these particles were morphologically abnormal when examined by transmission electron microscopy, displaying a previously described abnormally condensed nucleoid. Chronically infected restrictive cell lines producing stable levels of phenotypically vif-negative HIV-1 particles could prove particularly useful in further studies on the function of Vif in the virus life cycle.

The human immunodeficiency virus type 1 Vpr transactivator: cooperation with promoter-bound activator domains and binding to TFIIB

Since the first report documenting that HIV-1 Vpr was involved in the stimulation of transactivation of several unrelated promoters, little additional information has been reported. By using transient transfection experiments, we confirmed and extended these previously reported data. Further in vivo experiments showed that Vpr can co-operatively stimulate transactivation activity of a minimal promoter containing one GAL4 DNA-binding site, when it is co-expressed with different heterologous activator domains fused to GAL4 DNA-binding domain. Thus, Vpr could transactivate in concert with an activator domain, but has no effect on the transactivation of a minimal promoter in the absence of activator protein. To investigate whether Vpr can interact with components of the basal transcriptional machinery, in vitro protein-protein binding assays were performed using either translated, radiolabeled Vpr or TFIIB proteins and glutathione S-transferase Vpr or TFIIB chimeric proteins. We demonstrated that the portion of Vpr ranging from amino acids 15 to 77 interacts specifically with the basal transcription factor TFIIB. Also, our data indicated that the N-terminal domain of TFIIB is required for the interaction.

Human immunodeficiency virus type 1 Vpr protein binds to the uracil DNA glycosylase DNA repair enzyme

The role of the accessory gene product Vpr during human immunodeficiency virus type 1 infection remains unclear. We have used the yeast two-hybrid system to identify cellular proteins that interact with Vpr and could be involved in its function. A cDNA clone which encodes the human uracil DNA glycosylase (UNG), a DNA repair enzyme involved in removal of uracil in DNA, has been isolated. Interaction between Vpr and UNG has been demonstrated by in vitro protein-protein binding assays using translated, radiolabeled Vpr and UNG recombinant proteins expressed as a glutathione S-transferase fusion protein. Conversely, purified UNG has been demonstrated to interact with Vpr recombinant protein expressed as a glutathione S-transferase fusion protein. Coimmunoprecipitation experiments confirmed that Vpr and UNG are associated within cells expressing Vpr. By using a panel of C- and N-terminally deleted Vpr mutants, we have determined that the core protein of Vpr, spanning amino acids 15 to 77, is involved in the interaction with UNG. We also demonstrate by in vitro experiments that the enzymatic activity of UNG is retained upon interaction with Vpr.

Peripheral blood mononuclear cells produce normal amounts of defective Vif- human immunodeficiency virus type 1 particles which are restricted for the preretrotranscription steps

Previous studies have demonstrated the absence of viral replication of Vif- mutants in stimulated primary blood mononuclear cells (PBMC). Human immunodeficiency virus type 1 strain NDK Vif- mutants were propagated on the semipermissive CEM cell line, and the viral stock obtained was compared with the wild-type virus during a single cycle in PBMC. The Vif- virus was able to enter PBMC with the same efficiency as the wild type, as demonstrated by quantification of the strong-stop cDNA, and retrotranscription was observed for both viruses within 4 h postinfection. Using a PCR assay with an Alu-long terminal repeat pair of primers, we detected integration for both the wild-type and Vif- viruses. We then used qualitative and quantitative reverse transcription-mediated PCR techniques to study the steady-state level of intracellular and extracellular viral RNAs. All mRNA species were detected in PBMC infected with the wild-type virus or with the Vif- virus 36 h postinfection. Furthermore, quantification of viral RNA released from infected cells demonstrated similar levels of virus produced after a unique cycle of replication. However, the Vif- virus obtained after one replication cycle in PBMC was unable to initiate retrotranscription in permissive target cells. These data strongly suggest that the failure to infect target cells is due to a defect in the formation of the viral particle in PBMC.

The visna transcriptional activator Tat: effects on the viral LTR and on cellular genes

U937 promonocytic cells, either treated or untreated with phorbol-esters, were used for transient expression assays. We analyzed a series of visna LTR plasmids containing either the AP-1 or the AP-4 or both target responsive sequences for visna Tat transactivation. A 5' deletion mutant of the LTR containing a truncated AP-4 target sequence lost the Tat-mediated transactivation, while phorbol ester-mediated transactivation was not affected. Furthermore, the absence of this AP-4 sequence dramatically decreased the additive effect observed when U937 cells were both treated by phorbol ester and expressed the tat gene product, suggesting a high interdependence of the AP-1 and AP-4 sequences for the regulation of the transcription driven by the visna LTR. The c-Jun/AP-1 factor was a prerequisite for the modulation of the activity of the LTR since no Tat-mediated transactivation was found when transfection experiments were carried out in F9 teratocarcinoma cells which are deficient for AP-1 activity. Because the Tat product enhanced the transcription of the visna LTR via the AP-1 site, we asked whether this viral factor could regulate the expression of cellular factors involved in one of the cellular activation pathways. Northern analysis of U937 cells clearly indicated that visna Tat promoted the c-jun mRNA expression, in contrast to the c-fos mRNA expression. Next, we examined nuclear extracts prepared at various times after infection of permissive ovine cells with visna virus, and showed an increased level in the c-Jun DNA binding activity. These data indicated that viral infection can induce a cellular activation pathway in permissive cells.

HIV1 infection of human monocytes and macrophages promotes induction or translocation of NF-KB-related factors

In 1991, we demonstrated, using electrophoretic mobility shift assays, that 3 different factors (termed B1, B2 and B3) with affinity for the KB-enhancer target sequence were specifically detected in nuclear extracts from HIV1-infected monocytes and macrophages. The B2 factor was induced in the nuclei of these cells only upon HIV1 infection. The B3 factor was only slightly evident in nuclei of uninfected cells but was readily detectable in nuclei of infected monocytes. Its expression remained very low in nuclei of HIV1-infected macrophages. In this paper, we demonstrate that the B2 factor is expressed in the cytosol of monocytes and macrophages as a DNA-binding protein, indicating that it is not associated with an inhibitor (IKB). This factor remained clustered in the cytosol and was translocated to the nuclei only after HIV1 infection. The B3 factor is detected in the cytosol only when cells are HIV1-infected. The role of HIV1 infection in the expression and the translocation of these factors is discussed.

Induction of NF-KB during monocyte differentiation by HIV type 1 infection

The production of human immunodeficiency virus type 1 (HIV-1) progeny was followed in the U937 promonocytic cell line after stimulation either with retinoic acid or PMA, and in purified human monocytes and macrophages. Electrophoretic mobility shift assays and Southwestern blotting experiments were used to detect the binding of cellular transactivation factor NF-KB to the double repeat-KB enhancer sequence located in the long terminal repeat. PMA treatment, and not retinoic acid treatment of the U937 cells acts in inducing NF-KB expression in the nuclei. In nuclear extracts from monocytes or macrophages, induction of NF-KB occurred only if the cells were previously infected with HIV-1. When U937 cells were infected with HIV-1, no induction of NF-KB factor was detected, whereas high level of progeny virions was produced, suggesting that this factor was not required for viral replication. These results indicate that in monocytic cell lineage, HIV-1 could mimic some differentiation/activation stimuli allowing nuclear NF-KB expression.

Induction of NF-KB during monocyte differentiation by HIV type 1 infection

The production of human immunodeficiency virus type 1 (HIV-1) progeny was followed in the U937 promonocytic cell line after stimulation either with retinoic acid or PMA, and in purified human monocytes and macrophages. Electrophoretic mobility shift assays and Southwestern blotting experiments were used to detect the binding of cellular transactivation factor NF-KB to the double repeat-KB enhancer sequence located in the long terminal repeat. PMA treatment, and not retinoic acid treatment of the U937 cells acts in inducing NF-KB expression in the nuclei. In nuclear extracts from monocytes or macrophages, induction of NF-KB occurred only if the cells were previously infected with HIV-1. When U937 cells were infected with HIV-1, no induction of NF-KB factor was detected, whereas high level of progeny virions was produced, suggesting that this factor was not required for viral replication. These results indicate that in monocytic cell lineage, HIV-1 could mimic some differentiation/activation stimuli allowing nuclear NF-KB expression.

Differences in replication and cytopathogenicity of human immunodeficiency virus type 1 (HIV-1) are not determined by long terminal repeats (LTR)

The growth properties of molecular clones of a highly cytopathic Zairian HIV1-NDK and prototype viruses were compared to correlate genetic variations with biological changes. The cloned HIV1-NDK retained the highly replicating cytopathic phenotype and formed larger syncytia than the prototype. One of the major differences in the alignment of the nucleotide sequence of the HIV1-NDK and HIV1-BRU prototypes was localized in the negative regulatory element (NRE) of the long terminal repeat (LTR). In a chloramphenicol acetyl transferase (CAT) assay, we failed to detect a significant difference between LTR promoter activity of the prototype and HIV1-NDK, suggesting that the LTR of both phenotypes had a similar function. The complete recombinant provirus DNA molecules bearing HIV1 LTR derived from one phenotype and the rest of the genomes from the other phenotype were constructed and transfected. The high cytopathogenicity of both the original and the chimeric viruses was correlated with the high speed of virus replication. Cytopathogenicity, morphology of syncytia, and replication kinetics of the recombinant viruses were determined by the functions coded within an internal part of HIV1 genome, covering the gag to env region, which were, however, not within LTR.

The env gene variability is not directly related to the high cytopathogenicity of an HIV1 variant

HIV1-NDK is a Zairian HIV1 isolate which is unique because of its high cytopathic effect on T lymphoblastoid cell lines. Its sequence analysis has indicated 30% divergence with HIV1-LAV/BRU HTLVIII B prototype in the env gene encoding for the envelope glycoprotein gp120. In order to correlate the highly cytopathic properties with the env genetic variability, recombinants between the HIV1 prototype and HIV1-NDK have been constructed, including HIV1-NDK env gene, and their cytopathic phenotypes were analyzed. The viral hybrid containing all HIV1 prototype sequences except a large fragment including the total HIV1-NDK env gene remained at a low cytopathic phenotype. Our results suggest that sequences other than the env gene namely p18 gag, vif, and vpr are required for the high virulence of HIV1-NDK.

Nucleotide sequence of HIV1-NDK: a highly cytopathic strain of the human immunodeficiency virus

A highly cytopathic strain of HIV1, named HIV1-NDK, has been isolated from a Zaïrian patient affected with AIDS. This isolate is 10(4) times more cytopathic and infectious than the prototype. To correlate the high cytopathic properties of this strain with genetic variations, we have cloned and sequenced the genome of this isolate. The principal feature which could be drawn from the fine analysis of the HIV1-NDK sequence is that the variability is not clustered in one particular region but rather spread out all along the genome. Only minor differences seem to be responsible for the acute biological effect of HIV1-NDK.

Recognition of oligonucleotide-encoded T cell epitopes introduced into a gene unrelated to the original antigen

We have previously demonstrated that H-2Kd-restricted CTL specific for HLA-CW3 or HLA-A24 can recognize synthetic peptides corresponding to residues 170-182 of the HLA molecules. Synthetic oligonucleotides encoding region 170-182 of CW3 or A24 were inserted into the influenza nucleoprotein (NP) gene. We demonstrate herein that P815 (H-2d) cells transfected with the NP-oligo recombinant genes are specifically lysed by HLA-specific Kd-restricted CTL clones. Our results imply that there must be a high degree of flexibility for the expression of T cell epitopes in different molecular contexts.

A study of functionally active amino acids involved in the interaction of HLA-A2 or HLA-A3 molecules with cytolytic T lymphocytes

A large series of HLA-A2/HLA-A3 recombinant genes were generated by using the in vivo recombination technique. These genes have each been modified in the last two-thirds of the third exon such that one or several HLA-A2-specific substitutions have been made in the HLA-A3 gene and vice versa. The recombinant genes were transfected into the murine cell line P815 and the transfectants were used as targets for a series of 20 human CTL lines or clones specific for HLA-A2 or HLA-A3, or restricted by HLA-A2 and specific for influenza A. Several patterns of anti-HLA-A2, anti-HLA-A3, and HLA-A2-restricted anti-influenza CTL activity were observed and when uncloned cell lines were studied, a progressive selection of some clones with a similar pattern of activity was regularly found. From the comparison of these different patterns the following conclusions can be drawn: 1) In most but not all cases both domains of the class I molecule were essential for CTL recognition, but residue 152 was critically important for the majority of CTL tested; 2) amino acids 114/116 were also critical in most cases, and their position close to amino acid 152 in the tertiary structure of the molecule may have some functional significance; and 3) amino acid 161, although highly conserved, plays an unexpected but very important role in CTL function.

Epitope mapping of HLA-B27 and HLA-B7 antigens by using intradomain recombinants

To study the HLA-B7 and HLA-B27 antigenic determinants, hybrid genes between these two alleles were constructed by in vivo recombination in Escherichia coli. After transfection of these genes into P815 (high transfection efficiency recipient) murine cells, the bindings of Bw6, HLA-B7, and HLA-B27 allele-specific mAb were studied, as well as that of human anti-HLA-B7 and anti-HLA-B27 monospecific alloantisera. Most of the HLA-B7 antigenic determinants were assigned to the first external domain of the molecule. Four different epitopic areas could be defined: the Bw6 epitope was associated with residues 82 and 83; the BB7.1 epitope to amino acids 63, 67, and 70; the MB40.2 and MB40.3 epitope to amino acid sequence 177-180, and human alloantisera identified as an epitope associated with residue 9. HLA-B27 antigenicity studied by TM-1 mAb was found to involve residues 77 and 80 in the alpha-1 domain. Results obtained with human monospecific alloantisera allowed the definition of an additional allospecific site associated with the NH2 terminal part on the alpha-1 domain of HLA-B27. Epitope mapping fits with data obtained by sequence comparisons and is discussed with reference to the crystallographic three-dimensional structure of the HLA-A2 molecule.

Epitope mapping of HLA-B27 and HLA-B7 antigens by using intradomain recombinants

To study the HLA-B7 and HLA-B27 antigenic determinants, hybrid genes between these two alleles were constructed by in vivo recombination in Escherichia coli. After transfection of these genes into P815 (high transfection efficiency recipient) murine cells, the bindings of Bw6, HLA-B7, and HLA-B27 allele-specific mAb were studied, as well as that of human anti-HLA-B7 and anti-HLA-B27 monospecific alloantisera. Most of the HLA-B7 antigenic determinants were assigned to the first external domain of the molecule. Four different epitopic areas could be defined: the Bw6 epitope was associated with residues 82 and 83; the BB7.1 epitope to amino acids 63, 67, and 70; the MB40.2 and MB40.3 epitope to amino acid sequence 177-180, and human alloantisera identified as an epitope associated with residue 9. HLA-B27 antigenicity studied by TM-1 mAb was found to involve residues 77 and 80 in the alpha-1 domain. Results obtained with human monospecific alloantisera allowed the definition of an additional allospecific site associated with the NH2 terminal part on the alpha-1 domain of HLA-B27. Epitope mapping fits with data obtained by sequence comparisons and is discussed with reference to the crystallographic three-dimensional structure of the HLA-A2 molecule.

A study of functionally active amino acids involved in the interaction of HLA-A2 or HLA-A3 molecules with cytolytic T lymphocytes

A large series of HLA-A2/HLA-A3 recombinant genes were generated by using the in vivo recombination technique. These genes have each been modified in the last two-thirds of the third exon such that one or several HLA-A2-specific substitutions have been made in the HLA-A3 gene and vice versa. The recombinant genes were transfected into the murine cell line P815 and the transfectants were used as targets for a series of 20 human CTL lines or clones specific for HLA-A2 or HLA-A3, or restricted by HLA-A2 and specific for influenza A. Several patterns of anti-HLA-A2, anti-HLA-A3, and HLA-A2-restricted anti-influenza CTL activity were observed and when uncloned cell lines were studied, a progressive selection of some clones with a similar pattern of activity was regularly found. From the comparison of these different patterns the following conclusions can be drawn: 1) In most but not all cases both domains of the class I molecule were essential for CTL recognition, but residue 152 was critically important for the majority of CTL tested; 2) amino acids 114/116 were also critical in most cases, and their position close to amino acid 152 in the tertiary structure of the molecule may have some functional significance; and 3) amino acid 161, although highly conserved, plays an unexpected but very important role in CTL function.

Hybrid genes between HLA-A2 and HLA-A3 constructed by in vivo recombination allow mapping of HLA-A2 and HLA-A3 polymorphic antigenic determinants

HLA-A2 and -A3 genes have been modified in their third exon (second domain) by using in vivo recombination. In this method Escherichia coli are transfected with a plasmid which contains two highly homologous sequences (e.g., the third exons of HLA-A2 and -A3) and has been linearized by cleavage between these two sequences. Circularization takes place in the bacteria by homologous recombination leading to hybrid A2-A3 sequences. The analysis by DNA sequencing of a number of such recombinants shows that they indeed occur by homologous recombination (no insertions or deletions) and that the probability of crossing over decreases as the distance from the free end of DNA in the homologous region increases. No double recombinants were observed. These hybrid exons were reinserted into either HLA-A2 or HLA-A3 genes, thus generating a panel of functional hybrid genes containing one or several HLA-A2 specific substitutions in an HLA-A3 background or vice versa. These genes were expressed by transfection into murine P815-high transfection efficiency recipient cells. Serologic analysis leads to the conclusion that expression of polymorphic antigenic determinants specific for HLA-A2 (detected with M58, A2A28M1, and CR11.351 mAb) is linked to the presence of threonine residue (amino acid (AA) 142) and/or histidine residue (AA 145) and valine residue (AA 152). The expression of specific HLA-A3 polymorphic determinants (recognized by GAP-A3 mAb) is correlated with the existence of a asparagine residue (AA 127) and a aspartic residue (AA 161). But aspartic residue 161 contributes with glutamic acid residue 152 in the formation of the A3 epitope recognized by the anti-A3 mAb X1.23.2.

Hybrid genes between HLA-A2 and HLA-A3 constructed by in vivo recombination allow mapping of HLA-A2 and HLA-A3 polymorphic antigenic determinants

HLA-A2 and -A3 genes have been modified in their third exon (second domain) by using in vivo recombination. In this method Escherichia coli are transfected with a plasmid which contains two highly homologous sequences (e.g., the third exons of HLA-A2 and -A3) and has been linearized by cleavage between these two sequences. Circularization takes place in the bacteria by homologous recombination leading to hybrid A2-A3 sequences. The analysis by DNA sequencing of a number of such recombinants shows that they indeed occur by homologous recombination (no insertions or deletions) and that the probability of crossing over decreases as the distance from the free end of DNA in the homologous region increases. No double recombinants were observed. These hybrid exons were reinserted into either HLA-A2 or HLA-A3 genes, thus generating a panel of functional hybrid genes containing one or several HLA-A2 specific substitutions in an HLA-A3 background or vice versa. These genes were expressed by transfection into murine P815-high transfection efficiency recipient cells. Serologic analysis leads to the conclusion that expression of polymorphic antigenic determinants specific for HLA-A2 (detected with M58, A2A28M1, and CR11.351 mAb) is linked to the presence of threonine residue (amino acid (AA) 142) and/or histidine residue (AA 145) and valine residue (AA 152). The expression of specific HLA-A3 polymorphic determinants (recognized by GAP-A3 mAb) is correlated with the existence of a asparagine residue (AA 127) and a aspartic residue (AA 161). But aspartic residue 161 contributes with glutamic acid residue 152 in the formation of the A3 epitope recognized by the anti-A3 mAb X1.23.2.

Creation of an HLA-A2/HLA-Aw69 alloantigenic determinant on an HLA-A3 molecule by site-directed mutagenesis

The HLA-A2 and HLA-Aw69 molecules share an antigenic determinant not expressed by HLA-Aw68 and HLA-A3. Comparison of the amino acid (aa) sequences of these molecules and previous studies of the antigenic determinant expressed by different HLA-A2 X HLA-A3 hybrid molecules had established that three aa at positions 95, 97, and 107 were possibly involved in the formation of this determinant. The HLA-A3 gene was therefore mutagenized to replace successively at these positions the HLA-A3-specific aa by the HLA-A2 residues. A single substitution at position 107 of a glycine by a tryptophan residue is sufficient for full expression by HLA-A3 molecules of the HLA-A2/Aw69 shared antigenic determinant without modification of the other serological reactivities characteristic of the HLA-A3 molecules. Previous studies of ethyl methanesulfonate mutants having shown the involvement of aa 161 in this determinant, we assume that the two aa residues 107 and 161 are close to each other.

Creation of an HLA-A2/HLA-Aw69 alloantigenic determinant on an HLA-A3 molecule by site-directed mutagenesis

The HLA-A2 and HLA-Aw69 molecules share an antigenic determinant not expressed by HLA-Aw68 and HLA-A3. Comparison of the amino acid (aa) sequences of these molecules and previous studies of the antigenic determinant expressed by different HLA-A2 X HLA-A3 hybrid molecules had established that three aa at positions 95, 97, and 107 were possibly involved in the formation of this determinant. The HLA-A3 gene was therefore mutagenized to replace successively at these positions the HLA-A3-specific aa by the HLA-A2 residues. A single substitution at position 107 of a glycine by a tryptophan residue is sufficient for full expression by HLA-A3 molecules of the HLA-A2/Aw69 shared antigenic determinant without modification of the other serological reactivities characteristic of the HLA-A3 molecules. Previous studies of ethyl methanesulfonate mutants having shown the involvement of aa 161 in this determinant, we assume that the two aa residues 107 and 161 are close to each other.

Recognition of hybrid HLA molecules expressed on murine P815 cells using human alloreactive cytotoxic T lymphocytes

The HLA-A2 and -A3 genes were used to construct intra-exon hybrids in which part of the third exon (corresponding to the second domain) was of one type and the rest of the other. Murine P815 cells expressing these hybrid constructs were assayed with human alloreactive cytotoxic T-lymphocyte lines specific for either HLA-A2 or HLA-A3. Specific recognition patterns were obtained which indicate that, in some cases, a small portion of the HLA-A2 sequence in an HLA-A3 background is sufficient for recognition by HLA-A2-specific cytotoxic T cells.

Serological and structural analysis of HLA class I molecules: beta 2-microglobulin interacts with the two external domains of the HLA class I heavy chain

The serological reactivities of HLA class I molecules were studied in relation to structural modifications of these molecules, including shuffling of external exons and exchange of human beta 2-microglobulin for beta 2-microglobulin from different species. Two major clusters (I and II) of monomorphic and polymorphic antigenic determinants could be delineated. beta 2-Microglobulin participates in the formation of the two clusters, indicating that the light chain interacts tightly with the two external domains of the HLA class I heavy chain. However, external molecules can modify these interactions and alter the antigenic structure of the overall molecule. Thus, fixation on HLA class I molecules of the Fab fragment of a monoclonal antibody directed at antigenic determinants associated with cluster II resulted in enhanced fixation of a monoclonal antibody (B10.6) related to cluster I. The structural and functional implications of these results are discussed.

Transfection of murine LMTK- cells with purified HLA class I genes. VII. Association of allele- and locus-specific serological reactivities with respectively the first and second domains of the HLA-B7 molecule

The individual contributions of the first two external domains of the HLA-B7 heavy chain to the expression of allele-specific (B7) and locus-specific (B and C) antigenic determinants were investigated using hybrid class I genes. Hybrid genes were constructed in vitro by exon shuffling between the parent genes HLA-B7, HLA-Cw3, HLA-A3, and H-2Kd, and their expression was monitored following transfection into mouse L cells. The results show that most allele-specific antigenic determinants are associated with the first external domain of the B7 heavy chain, whereas all the locus-specific antigenic determinants tested map to the second external domain.

Rat immunoglobulin delta heavy chain gene: nucleotide sequence derived from cloned cDNA

Rat immunoglobulin delta heavy-chain mRNA has been isolated. RNA blot analysis revealed that this mRNA with a length of 1.8 kb encodes for the secreted form of IgD. The corresponding cDNA was cloned in plasmid pBR322 and its sequence was determined. The hybrid plasmid contains a 775-bp insert comprising a partial C delta 1 sequence and complete C delta H, C delta 3, C delta DC and 3' untranslated sequences. Rat and mouse IgD amino acid sequences show striking homology in C delta 3 and C delta DC regions.

Rat IgD myeloma protein: cell-free translation of the delta mRNA and biochemical analysis of intracellular and membrane delta chain

The analysis of IgD molecules produced by the tumor-derived IR 731 cell line showed that these molecules are not secreted and are only present at the cell surface as covalent dimers of 48 000 dalton delta chains. The original IR 731 tumor secreted complete IgD; thus, the disppearance of secretion in the cell line was correlated with the absence of light chain synthesis. The mRNA coding for the cell line delta chain was isolated and translated. The analysis of the translated delta chain (mol. wt.: 40 000) confirmed the absence of a region having the size of a domain as previously shown by partial amino acid sequence. The observation that the absence in delta chain of this region, which comprises most of the CH2 domain, could be a general feature of murine species is discussed.

Putative conformation of mouse Fc gamma-receptor

Three cell surface molecules (m.w. = 115,000, 90,000, and 70,000) binding to the Fc portion of complexed IgG have been isolated from the murine mastocytoma line P815. Various results suggested that the 90,000 and 70,000 dalton components are generated from the 115,00 dalton molecule by spontaneous proteolytic clevages and release of 23,000 dalton fragments. It was demonstrated that these cleavages occur during cell culture and not when freshly harvested mouse spleen cells are used as an Fc gamma R cell source. The survey of the Fc gamma R molecular forms obtained from P815 and spleen cells together with their reduction products led us to conclude that the mouse Fc gamma-receptor for complexed IgG is a single chain molecule (115,000 daltons) folded into five globular subunits (m.w. eta 23,000) linked by loose connecting regions accessible to proteolytic enzymes. Three of these subunits that compose the 70,000-dalton fragment are linked by di-sulfide bonds. Furthermore, a 140,000-dalton Fc gamma-binding molecule, not identified after cell surface labeling, could be detected after internal labeling. This component could be a cytoplasmic precursor of the Fc gamma R molecule. The structural model we present here might in addition shed some light on the discrepancy that appears through the various biochemical studies performed so far on Fc gamma-receptors.

Putative conformation of mouse Fc gamma-receptor

Three cell surface molecules (m.w. = 115,000, 90,000, and 70,000) binding to the Fc portion of complexed IgG have been isolated from the murine mastocytoma line P815. Various results suggested that the 90,000 and 70,000 dalton components are generated from the 115,00 dalton molecule by spontaneous proteolytic clevages and release of 23,000 dalton fragments. It was demonstrated that these cleavages occur during cell culture and not when freshly harvested mouse spleen cells are used as an Fc gamma R cell source. The survey of the Fc gamma R molecular forms obtained from P815 and spleen cells together with their reduction products led us to conclude that the mouse Fc gamma-receptor for complexed IgG is a single chain molecule (115,000 daltons) folded into five globular subunits (m.w. eta 23,000) linked by loose connecting regions accessible to proteolytic enzymes. Three of these subunits that compose the 70,000-dalton fragment are linked by di-sulfide bonds. Furthermore, a 140,000-dalton Fc gamma-binding molecule, not identified after cell surface labeling, could be detected after internal labeling. This component could be a cytoplasmic precursor of the Fc gamma R molecule. The structural model we present here might in addition shed some light on the discrepancy that appears through the various biochemical studies performed so far on Fc gamma-receptors.

Biochemical characterization of an Fc receptor of rabbit lymphocytes

Isolation of Fc-binding molecules was performed by complexing IgG antibodies and the corresponding antigens in lysates of radiolabeled rabbit lymphoid cells. A single-chain molecule of 110 000 apparent mol. wt. (unreduced) or 120 000 (reduced) was observed in sodium dodecyl sulfate polyacrylamide gel electrophoresis when the antibodies were in the IgG form but not as F(ab')2. This molecule was very susceptible to proteolysis, but the fragments thus produced remained associated by disulfide bridges, and the binding properties of the molecule were conserved. The molecule and its proteolytic fragments (mol. wts. 75 000, 45 000 and 20 000) were very similar to those obtained for the mouse Fc receptor under similar conditions, and therefore the molecule was designated as rabbit Fc receptor. Among several precipitating systems used, some Ig-anti-Ig complexes appeared to be the most efficient in coprecipitating the rabbit Fc receptor. Remarkably high titers of Fc receptor were found on lymphocyte membrane of infected rabbits, in agreement with a possible role of this molecule in immune regulation.

Identification of an IgD-like surface immunoglobulin on rabbit lymphocytes

Rabbit immunoglobulin antigen receptor molecules were analyzed by electrophoresis in sodium dodecyl sulfate polyacrylamide gels. By sequential precipitation, using first anti-mu and then anti-L chain antisera, two different immunogloublins of similar molecular weight could be demonstrated. After tryptic digestion, two fractions were identified: an IgMs and an Fab fragment, the latter appearing after a few minutes of incubation. Thus, as in man and in the mouse, two main immunoglobulin antigen receptors were found in the rabbit. One receptor on rabbit lymphocytes is an IgMs molecule, and the other is easily split in the hinge region like human and mouse IgD receptors. In addition, a molecule similar to the mouse Fc receptor was nonspecifically precipitated.

[beta2-Microglobulin and experimental nephropathies in macacus monkey (author's transl)]

In the monkey, the action of four renal toxics : lead acetate, sodium maleate, cadmium chloride and sodium chromate was compared. Tubulopathies were obtained only with cadmium chloride and sodium chromate with in the best cases about 16 mg/l of beta2-microglobulin (beta2m) in the urine. Monkey and human beta2m have the same molecular weight and are antigenically similar. However, they differed in electrophoretic mobility, the monkey beta2m being slightly more cathodic.

[beta2-Microglobulin in human seminal fluid (author's transl)]

The expression of human beta2-microglobulin (beta2m) on human spermatozoa cell surface was investigated by cytotoxicity and immunofluorescence tests. beta2m was also found in human seminal fluid by use of immunochemical techniques. Seminal fluids obtained from couples with infertility problems were tested for beta2m, albumin and total proteins concentration. A higher level of beta-2m was found in azoospermia compared with that of normal sperms.

A rapid and sensitive method using immunological nephelometric analysis to evaluate the gel-filtration method. (Application to the diagnosis of rubella)

Immunological nephelometric analysis has been shown to be a more sensitive method than either immunoelectrophoresis or gel-diffusion for testing the gel-filtration method of human immunoglobulins sera. This method has the advantages of facility, rapidity and sensitivity. We have compared this method to radial immunodiffusion. This method can be applied to locate with precision any antigens after gel-filtration or ion-exchange chromatography.