Involvement of nitric oxide in target-cell lysis and DNA fragmentation induced by murine natural killer cells

Although it has been recognized for sometime that target cells destroyed by natural killer (NK) cells die largely by apoptosis, the underlying mechanisms are not fully understood. The aim of the present study was to examine the role of nitric oxide (NO) in mediating murine NK-cell-induced killing of YAC-1 lymphoma cells. NK calls induced extensive release of 125I-DNA and 51Cr from YAC-1 cells. The target killing ability of NK cells was associated with an increased production of NO as measured by concentrations of nitrite in the culture medium. That YAC-1 killing resulted, in part, from the production of NO was confirmed by the significant protection of cell lysis in L-arginine-depleted medium and by approximately 30 % attenuation of cell lysis and DNA fragmentation by an inhibitor of NO synthase, NG-nitro-L-arginine methyl ester (L-NAME) in a culture medium containing 1 mmol/L L-arginine. Fluorescence microscopic examination of YAC-1 cells showed the presence of changes in nuclear morphology characteristic for apoptosis. The percentage of apoptotic cells was markedly decreased by L-NAME. Further evidence for apoptosis is provided by the specific pattern of internucleosomal DNA fragmentation both in the absence and presence of L-NAME. During target-cell killing, an increased oxidation of intracellularly trapped dichlorofluorescein was observed in cells labeled with an antimouse NK-cell monoclonal antibody, as measured by flow cytometry. These increases were effectively prevented by L-NAME, but not W-13, an inhibitor of calmodulin. The ability of NO to induce cell lysis and DNA fragmentation in YAC-1 cells was further demonstrated by exposing tumor cells to chemically generated NO. Taken together, these observations suggest a role for NO as one of the mediators of NK-cell-mediated DNA fragmentation and cell lysis.

Potassium chloride pulse enhances mitogen-activated protein kinase activity in rat hippocampal slices

Mitogen-activated protein (MAP) kinases have been implicated in multiple responses to extracellular stimuli. In this study we show that MAP kinase activity is enhanced after a KCl pulse. This activation correlates with an increased tyrosine phosphorylation of a 42-kDa protein as determined by antiphosphotyrosine immunoblot. The same band is found in an anti-MAP kinase immunoblot. Activity is enhanced within 1 min, reaches a maximum at 2 min, and returns to basal level after 10 min. A second peak of activity is observed between 12 and 30 min. The activation is completely blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), showing the involvement of the AMPA type of glutamate receptor. Partial inhibition of MAP kinase activation by 2-amino-5-phosphonovalerate (APV) also shows the involvement of the NMDA receptor. Because the KCl pulse used induces long-term potentiation (LTP) in rat hippocampal slice, we conclude that MAP kinase may be involved in neuronal transduction events leading to LTP.

Flow-cytometric characterization of hematopoietic cells in non-pregnant human endometrium

PROBLEM

Immunologic evaluation and quantitation of hematopoietic cells in human endometrium has been difficult to perform, particularly in nonpregnant subjects. In this study, we describe a method for the flow-cytometric characterization of hematopoietic cells present in the endometrium of non-pregnant women.

METHOD

Endometrial biopsy samples from normal donors were first mechanically disrupted and filtered to generate a single-cell suspension of leukocyte-enriched endometrial cells. Cells were labeled with a panel of monoclonal antibodies, stained with propidium iodide (PI), and one- or two-color flow-cytometric analysis performed on cells excluding PI.

RESULTS

The methodology described in this study was highly reproducible in experiments evaluating the interrun and intrarun variability. We then determined the immunophenotypic profile of endometrial leukocytes from 12 normal females. The majority of leukocytes were T cells (CD3: 47%; CD4: 24%; CD8: 28%) with an important contingent of NK cells (CD56: 32%), the majority of which harbored the unusual CD16-CD56 bright phenotype, and a minority of B cells (CD20: 6%) and monocytes (CD14: 7%).

CONCLUSIONS

Flow cytometry can be used to assess antigen expression on the surface of endometrial leukocytes from nonpregnant women. In future studies, it will be possible to use this approach to investigate the role of immune cell populations in the endometrium of patients experiencing reproductive failure.

Oligoclonal expansion of CTLs directed against a restricted number of dominant minor histocompatibility antigens in hemopoietic chimeras

To understand how T cells respond to allogeneic minor histocompatibility Ags (MiHAs), we studied the fate of Thy-1.1+ lymphocytes, as well as their TCR usage and functional activity, in irradiated LP (Thy-1.2+) recipients transplanted with a mixture of C57BL/6 (Thy-1.2+) hemopoietic progenitors supplemented with either low or high numbers of B6.PL lymphocytes (Thy-1.1+). Mice transplanted with low numbers of T cells experienced a dramatic expansion (> or = 10(5)-fold) of donor Thy-1.1+/CD8+ cells during the first 15 days post-transplant. Flow-cytometric analysis and sequencing of junctional nucleotide sequences showed that the nature of this expansion was oligoclonal and involved primarily one or a few clones using V beta 5.1 or V beta 8.1 TCR elements. Expanded T lymphocyte populations displayed MHC-restricted cytotoxicity for a restricted number of MiHAs, that were found in only two peaks following fractionation of LP MiHAs by reverse-phase HPLC. Expansion of donor T cells was limited to the spleen, and short-lived in these recipients that became healthy long-term chimeras without any signs of graft-vs-host disease (GVHD). In contrast, mice transplanted with high numbers of T cells (GVHD+) showed proliferation of Thy-1.1+ donor cells not only in the spleen, but also in the thymus, and recipients died rapidly of GVHD. These results show that: 1) in the MiHA-incompatible transplantation setting, lack of GVHD cannot be explained simply by the absence of antihost T cell responses, 2) GVHD+ recipients present a massive thymic infiltration by donor mature T lymphocytes, and 3) antihost T cell responses are oligoclonal in nature and targeted to only a few MiHAs. These findings shed new light on the pathogenetic mechanisms involved in GVHD and on the selection of the T cell repertoire involved in response to immunodominant MiHAs.

Oligoclonal expansion of CTLs directed against a restricted number of dominant minor histocompatibility antigens in hemopoietic chimeras

To understand how T cells respond to allogeneic minor histocompatibility Ags (MiHAs), we studied the fate of Thy-1.1+ lymphocytes, as well as their TCR usage and functional activity, in irradiated LP (Thy-1.2+) recipients transplanted with a mixture of C57BL/6 (Thy-1.2+) hemopoietic progenitors supplemented with either low or high numbers of B6.PL lymphocytes (Thy-1.1+). Mice transplanted with low numbers of T cells experienced a dramatic expansion (> or = 10(5)-fold) of donor Thy-1.1+/CD8+ cells during the first 15 days post-transplant. Flow-cytometric analysis and sequencing of junctional nucleotide sequences showed that the nature of this expansion was oligoclonal and involved primarily one or a few clones using V beta 5.1 or V beta 8.1 TCR elements. Expanded T lymphocyte populations displayed MHC-restricted cytotoxicity for a restricted number of MiHAs, that were found in only two peaks following fractionation of LP MiHAs by reverse-phase HPLC. Expansion of donor T cells was limited to the spleen, and short-lived in these recipients that became healthy long-term chimeras without any signs of graft-vs-host disease (GVHD). In contrast, mice transplanted with high numbers of T cells (GVHD+) showed proliferation of Thy-1.1+ donor cells not only in the spleen, but also in the thymus, and recipients died rapidly of GVHD. These results show that: 1) in the MiHA-incompatible transplantation setting, lack of GVHD cannot be explained simply by the absence of antihost T cell responses, 2) GVHD+ recipients present a massive thymic infiltration by donor mature T lymphocytes, and 3) antihost T cell responses are oligoclonal in nature and targeted to only a few MiHAs. These findings shed new light on the pathogenetic mechanisms involved in GVHD and on the selection of the T cell repertoire involved in response to immunodominant MiHAs.

The plant response in pathogenesis, symbiosis, and wounding: variations on a common theme?

Upon interaction with pathogenic Pseudomonads or symbiotic Rhizobia, or after wounding by abrasion or insects, the plant reacts in superficially different ways, leading to either a close association or defense against the intruder. However, a closer examination reveals that similar genes and metabolic pathways are induced. This raises the possibility that signal perception and transduction proceed via similar pathways, leading to overlaps in the response reaction. This review compares current knowledge of the plant reaction to apparently different biotic and abiotic stimuli, and highlights that within the course of evolution similar response mechanisms were adapted to specific needs.

The impact of amniotic fluid volume assessed intrapartum on perinatal outcome

OBJECTIVE

Our purpose was to determine the value of routine intrapartum amniotic fluid volume assessment on perinatal outcome.

STUDY DESIGN

Patients admitted for labor and delivery who were ultimately delivered between January 1988 and June 1989 with a gestational age > or = 26 weeks and who had an intrapartum amniotic fluid index composed the study group. The amniotic fluid index was determined by the four-quadrant technique on admission to labor and delivery. Oligohydramnios was defined as an amniotic fluid index < or = 5 cm (n = 170), borderline oligohydramnios as an amniotic fluid index 5.1 to 8.0 cm (n = 261), and normal amniotic fluid volume as an amniotic fluid index 8.1 to 20 cm (n = 336). Nine patients with an amniotic fluid index > 20 cm were excluded from data analysis. The oligohydramnios and borderline oligohydramnios groups were compared with the normal group with regard to antenatal, intrapartum, and postpartum variables.

RESULTS

The groups had similar maternal age, parity, gestational age at delivery, and antenatal complications. Meconium-stained amniotic fluid occurred significantly less often in the oligohydramnios group compared with the normal group (relative risk 0.67, 95% confidence interval 0.49 to 0.92). However, variable decelerations occurred significantly more often in the oligohydramnios group compared with the normal group (relative risk 1.44, 95% confidence interval 1.12 to 1.87), and cesarean delivery for fetal distress also occurred significantly more often (relative risk 6.83, 95% confidence interval 1.55 to 30.4). There was no difference in Apgar scores or neonatal complications between groups. The efficacy of intrapartum-determined oligohydramnios predicting cesarean delivery for fetal distress gave a sensitivity of 78%, a specificity of 74%, a positive predictive value of 33%, and a negative predictive value of 95%.

CONCLUSION

The amniotic fluid index for detecting intrapartum oligohydramnios is a valuable screening test for subsequent fetal distress requiring cesarean delivery.

Immunodominant minor histocompatibility antigens expressed by mouse leukemic cells can serve as effective targets for T cell immunotherapy

Numerous minor histocompatibility antigens (MiHAs) show tissue-specific expression and can induce vigorous T cell responses. They therefore represent attractive targets for leukemia immunotherapy mediated by adoptive transfer of T cells. The main objective of this work was to determine whether MiHAs expressed by normal hematopoietic cells were present on leukemic cells and whether they could trigger lysis by cytotoxic T lymphocytes (CTLs). CTL assays showed that mouse leukemic cells of both lymphoid and myeloid lineages were sensitive to CTLs targeted toward some but not all MiHAs. In four out of four strain combinations in which we primed CTLs against immunodominant MiHAs, effectors killed leukemic blasts, whereas no cytotoxicity was observed when CTLs were targeted toward four immunorecessive MiHAs. Testing of HPLC fractions obtained from normal and leukemic cells provided molecular evidence that leukemic blasts expressed only some of the MiHAs found on normal mouse hematopoietic cells. Decreased density of H-2 class I molecules at the surface of leukemic cells suggests that down-regulation of genes encoding either class I molecules or proteins involved in antigen processing played a role in the aberrant expression of MiHAs. In vivo resistance to the leukemic cells by various strains of mice correlated with in vitro CTL activity. These results show that leukemic cells express only some (immunodominant) MiHAs and suggest that this subset of MiHAs represent prime targets for adoptive immunotherapy.

Graft-host tolerance in bone marrow transplant chimeras. Absence of graft-versus-host disease is associated with unresponsiveness to minor histocompatibility antigens expressed by all tissues

Because bone marrow (BM) transplantation is used with increasing frequency, it is important to elucidate the mechanisms involved in the establishment of tolerance to host minor histocompatibility antigens (MiHA) in recipients transplanted with T-cell-undepleted marrow grafts. We have previously shown that BM chimeras transplanted across MiHA barriers showed specific unresponsiveness to MiHA expressed on recipient-type concanavalin A blasts. Because expression of many MiHA is tissue-specific, we wanted to determine if chimera T lymphocytes would be tolerant to MiHA expressed by all host tissues and organs. To investigate this issue, we measured in vivo proliferation of lymphoid cells from normal C57BL/10 (B10) mice and (B10-->LP) chimeras in tissues and organs of lethally irradiated syngeneic and allogeneic recipients. Donor B10 cells were either untreated, or depleted with anti-Thy-1.2, anti-CD4, or anti-CD8 antibodies. Transplantation of B10 cells in LP recipients triggered an important T-cell-dependent 125I-dUrd uptake in several organs that involved both CD4+ and CD8+ cells. Using Thy-1-congeneic mice we showed that in long-term chimeras practically all CD4+ and CD8+ T lymphocytes were derived from hematopoietic progenitors and not from mature T cells present in the BM graft. When (B10-->LP) BM chimera cells were injected to secondary recipients, no proliferation was observed in any organ of LP hosts whereas normal proliferation was seen in H-2k allogeneic hosts. Thus, in these BM chimeras, tolerance encompasses MiHA expressed by all organs.

Eukaryotic selenocysteine inserting tRNA species support selenoprotein synthesis in Escherichia coli

Although the tRNA species directing selenocysteine insertion in prokaryotes differ greatly in their primary structure from that of their eukaryotic homologues they share very similar three-dimensional structures. To analyse whether this conservation of the overall shape of the molecules reflects a conservation of their functional interactions it was tested whether the selenocysteine inserting tRNA species from Homo sapiens supports selenoprotein synthesis in E. coli. It was found that the expression of the human tRNA(Sec) gene in E.coli can complement a lesion in the tRNA(Sec) gene of this organism. Transcripts of the Homo sapiens and Xenopus laevis tRNA(Sec) genes synthesised in vitro were amino-acylated by the E.coli seryl-tRNA ligase although at a very low rate and the resulting seryl-tRNA(Sec) was bound to and converted into selenocysteyl-tRNA(Sec) by the selenocysteine synthase of this organism. Selenocysteyl-tRNA(Sec) from both eukaryotes was able to form a complex with translation factor SELB from E.coli. Although the mechanism of selenocysteine incorporation into seleno-proteins appears to be rather different in E.coli and in vertebrates, we observe here a surprising conservation of functions over an enormous evolutionary distance.

Acquired C1 inhibitor deficiency as a result of an autoantibody to the reactive center region of C1 inhibitor

An autoantibody that we hypothesize to react with the reactive center of the plasma serine proteinase inhibitor, C1 inhibitor (C1INH), has been found in a patient with acquired C1INH deficiency. The Ab blocks the ability of C1INH to inhibit the hydrolysis of N-carbobenzyloxy-L-lysine thiobenzylester by purified C1s. A cryoprecipitate from the patient's plasma as well as the Ig fraction were able to block C1INH inhibition of C1s. The immunoaffinity purified Ab to C1INH from the patient's plasma Ig fraction neutralizes the inhibitory activity of C1INH in a dose-dependent manner and blocks the ability of normal C1INH to form a complex with C1s. The neutralizing activity of the purified Ab is reversed by a synthetic peptide that corresponds to the amino acid sequence in the P1 to P15 positions of the reactive center of C1INH but not by a 34-amino-acid trypsin peptide or 37-amino-acid elastase peptide derived from the C-terminus of C1INH. Western blot analysis indicated that the Ab is an oligoclonal Ig with kappa light chains.

Acquired C1 inhibitor deficiency as a result of an autoantibody to the reactive center region of C1 inhibitor

An autoantibody that we hypothesize to react with the reactive center of the plasma serine proteinase inhibitor, C1 inhibitor (C1INH), has been found in a patient with acquired C1INH deficiency. The Ab blocks the ability of C1INH to inhibit the hydrolysis of N-carbobenzyloxy-L-lysine thiobenzylester by purified C1s. A cryoprecipitate from the patient's plasma as well as the Ig fraction were able to block C1INH inhibition of C1s. The immunoaffinity purified Ab to C1INH from the patient's plasma Ig fraction neutralizes the inhibitory activity of C1INH in a dose-dependent manner and blocks the ability of normal C1INH to form a complex with C1s. The neutralizing activity of the purified Ab is reversed by a synthetic peptide that corresponds to the amino acid sequence in the P1 to P15 positions of the reactive center of C1INH but not by a 34-amino-acid trypsin peptide or 37-amino-acid elastase peptide derived from the C-terminus of C1INH. Western blot analysis indicated that the Ab is an oligoclonal Ig with kappa light chains.

Effects of lymphocyte subpopulations on the clonal assay of HPRT mutants: occupational exposure to cytostatic drugs

The mutagenic effect of occupational exposure to antineoplastic agents was studied in chemotherapy nurses and pharmacists using the T-lymphocyte clonal assay. A significant increase in mutant frequency was observed compared to controls. However, in the present study, cloning efficiency without selection (CEU) was significantly reduced in exposed personnel raising the possibility of an overestimation of the calculated MF. Changes in lymphocyte populations and clonal potential of T-cells were also observed following exposure. CEU was related to % CD4 cells but CE with selection (CETG) was not. Differences in clonal ability of T-cells under selective and unselective conditions coupled with differential lethal effect of antineoplastic agents on lymphocyte subsets may result in inaccurate estimation of MF.

Flow cytometric evaluation of the acrosome reaction of human spermatozoa: a new method using a photoactivated supravital stain

A flow cytometric assay using a double-stain method for the measurement of the acrosome reaction of human spermatozoa is described. The use of a stable photoactivated stain, ethidium monoazide, allowed evaluation of the viability of spermatozoa. This stain was more stable in fixed samples than propidium iodide, which is not bound covalently to DNA and is therefore removed readily during the washing procedure. The permeabilized acrosome was labelled with Pisum sativum agglutinin conjugated with fluoroisothiocyanate. Since this lectin binds to the acrosome and acrosomal contents, a decrease in the fluorescence intensity allows the cytometric evaluation of the acrosome reaction. Microscopic analysis and flow cytometric analysis were well correlated and cell sorting was performed to ensure the homogeneity of each different subpopulation encountered.

The formation of diselenide bridges in proteins by incorporation of selenocysteine residues: biosynthesis and characterization of (Se)2-thioredoxin

A system was devised which allows the efficient substitution of cysteine residues in a protein by selenocysteine. It involves overexpression of the respective gene with the aid of the T7 promotor/polymerase system in a cysteine auxotrophic strain. The induction of the T7 polymerase formation was performed in cysteine-supplemented medium followed by wash-out of the cysteine and production of the desired gene product in the presence of selenocysteine. The system was applied to substitute the two cysteine residues in Escherichia coli thioredoxin. Analysis of the purified gene product by electrospray mass spectrometry and HPLC revealed that both cysteine residues were replaced in approximately 75-80% of the protein, only one cysteine residue was substituted in about 5-10%, and no substitution had taken place in 12-17% of the protein. The occurrence of diselenide, seleno-sulfur, and disulfide bridges in the purified gene product was revealed by ES/MS and chemical modification studies. The diselenide bridge represents an entity in protein structures which has hitherto not been described. The redox property of the selenocysteine variant of thioredoxin [(Se)2-thioredoxin] was found to be substantially different from that of thioredoxin. Only the latter could be reduced under native conditions in the presence of an excess of beta-mercaptoethanol. The oxidized (Se)2-thioredoxin was then separated from the selectively reduced and carboxymethylated protein by anion-exchange chromatography. The purity of the isolated (Se)2-thioredoxin was at least 92%.

Evaluation of two new chromogenic media for detection of Salmonella in stools

A clinical collaborative study was conducted to compare two new chromogenic agar media, Rambach agar and the Salmonella Detection and Identification Medium (SMID) (bioMérieux, France), with two conventional media, Salmonella-Shigella agar and Hektoen agar. Thirty-nine Salmonella strains involving 14 serotypes were isolated from 1,454 stool specimens. After enrichment in a selective broth, 100% sensitivity was obtained with each medium. The SMID and Rambach agars are considerably more specific than the conventional media. Although SMID agar detects all Salmonella serotypes, it is not as specific as Rambach agar, which requires a complementary test (C8 esterase test) to detect all serotypes.

[Cancer after transplantation]

Transplantation is associated with an increased risk of cancer. The major factor favouring carcinogenesis is the degree of immunosuppression rather than the nature of the drug used. A large number of these tumours are virus-induced, reflecting an immune system deficiency in combating viral infection. The transplanted patient should be closely followed, both early after transplantation and consistently thereafter, for early detection of such complications.

Recognition of the mRNA selenocysteine insertion sequence by the specialized translational elongation factor SELB

In Escherichia coli the unusual amino acid selenocysteine is incorporated cotranslationally at an in-frame UGA codon. Incorporation of selenocysteine relies, in part, on the interaction between a specialized elongation factor, the SELB protein, and a cis-acting element within the mRNA. Boundary and toeprint experiments illustrate that the SELB-GTP-Sec-tRNA(Sec) ternary complex binds to the selenoprotein encoding mRNAs fdhF and fdnG, serving to increase the concentration of SELB and Sec-tRNA(Sec) on these mRNAs in vivo. Moreover, toeprint experiments indicate that SELB recognizes the ribosome-bound message and that, upon binding, SELB may protrude out of the ribosomal-mRNA track so as to approach the large ribosomal subunit. The results place the mRNA-bound SELB-GTP-Sec-tRNA(Sec) ternary complex at the selenocysteine codon (as expected) and suggest a mechanism to explain the specificity of selenocysteine insertion. Cis-acting mRNA regulatory elements can tether protein factors to the translation complex during protein synthesis.

Germline deletion in a neurofibromatosis type 2 kindred inactivates the NF2 gene and a candidate meningioma locus

Neurofibromatosis type 2 (NF2) is an autosomal dominant disease which predisposes to the development of schwannomas, meningiomas, ependymomas, and juvenile cataracts. The NF2 gene (NF2) has recently been isolated and maps to chromosome 22q12 between the loci D22S212 and D22S32. Deletion studies in sporadic and NF2 associated schwannomas and meningiomas, and the presence of inactivating mutations in NF2 in patients suggest that it acts as a tumor suppressor gene. A candidate meningioma gene (MEN) has also been isolated from the same interval. A new highly polymorphic (CA)n marker, D22S268, which maps very near to NF2, has allowed us to identify a kindred with three living affected individuals, where the disease is presumably caused by a large germline deletion. Fluorescence in situ hybridization and pulsed field gel electrophoresis confirm the presence of a 700kb deletion which includes the neurofilament heavy chain subunit gene locus (NEFH), D22S268, NF2 and the putative MEN gene. The absence of meningiomas in this pedigree raises doubts as to the existence of a separate MEN locus in this region. These results support the hypothesis that NF2 results from the inactivation of a tumor suppressor gene on chromosome 22q.

Solution structure of selenocysteine-inserting tRNA(Sec) from Escherichia coli. Comparison with canonical tRNA(Ser)

Selenocysteine-inserting tRNAs (or tRNA(Sec)) are structurally untypical tRNAs that are charged by seryl-tRNA synthetase before being recognized by the selenocysteine synthase that converts serine into selenocysteine. tRNA(Sec) from Escherichia coli contains 95 nucleotides and is the longest tRNA known to date, in contrast to canonical tRNA(Ser), 88 nucleotides-long. We have studied its solution conformation by chemical and enzymatic probing. Global structural features were obtained by cobra venom and S1 nuclease mapping, as well as by probing with Pb2+. Accessibilities of phosphate groups were measured by ethylnitrosourea probing. Information about positions in bases involved in Watson-Crick pairing, in stacking or in tertiary interactions were obtained by chemical probing with dimethylsulfate, diethylpyrocarbonate, kethoxal and carbodiimide. On the basis of these chemical data, a three-dimensional model was constructed by computer modeling and compared to that of canonical tRNA(Ser). tRNA(Sec) resembles tRNA(Ser) at the level of its T-arm and anticodon-arm conformations, as well as at the joining of the D- and T-loops by a tertiary Watson-Crick G19-C56 interaction. Its extra-long variable arm is a double-stranded structure closed by a four nucleotide loop that is linked to the body of the tRNA in a way different from that found in tRNA(Ser). As anticipated from the peculiar features of the sequence in the D-loop and at the junction of amino acid and D-arms, tRNA(Sec) possesses a novel but restricted set of tertiary interactions in the core of its three-dimensional structure: a G8-A21-U14 triple pair and a novel interaction between C16 of the D-loop and C59 of the T-loop. A third triple interaction involving C15-G20a-G48 is suggested but some experimental evidence for it is still lacking. It is furthermore concluded that the D-arm has six base-pairs instead of three, as in canonical class II tRNA(Ser), with the D-loop containing only four nucleotides. Finally, the amino acid accepting arm forms a stack of eight Watson-Crick base-pairs (instead of 7 in other tRNAs). The biological relevance of this model with regard to interaction with seryl-tRNA synthetase and enzymes from the selenocysteine metabolism is discussed.

Interaction of translation factor SELB with the formate dehydrogenase H selenopolypeptide mRNA

The SELB protein from Escherichia coli is a specialized elongation factor required for the UGA-directed insertion of the amino acid selenocysteine into selenopolypeptides. Discrimination of the UGA codon requires the presence of a recognition element within the mRNA, which is located at the 3' side of the UGA codon; a hairpin structure can be formed within this mRNA region. By gel shift assays, a specific interaction between SELB and the mRNA recognition element could be demonstrated. Footprinting experiments, using nucleases or iodine as cleaving agents, showed that SELB binds to the loop region of the hairpin structure. In the presence of selenocysteinyl-tRNA, SELB formed a complex with the charged tRNA and the mRNA. The results indicate that targeted insertion of selenocysteine is accomplished by the binding of the SELB protein to this mRNA recognition element, resulting in the formation of a selenocysteinyl-tRNA.SELB complex at the mRNA in the immediate neighborhood of the UGA codon.

[Immunodeficiency caused by graft versus host reaction. Extra-thymic effect of thymus in restoring immunity]

Cell-mediated immunity in lethally irradiated graft-versus-host mice can be restored after repopulation with syngeneic bone marrow cells and thymus grafting. The thymus is not only required for the maturation of T lymphocytes, but also for the inhibition of a radioresistant mechanism resulting in lymphoid cell rejection.

Coding from a distance: dissection of the mRNA determinants required for the incorporation of selenocysteine into protein

Incorporation of selenocysteine into proteins is directed by specifically 'programmed' UGA codons. The determinants for recognition of the selenocysteine codon have been investigated by analysing the effect of mutations in fdhF, the gene for formate dehydrogenase H of Escherichia coli, on selenocysteine incorporation. It was found that selenocysteine was also encoded when the UGA codon was replaced by UAA and UAG, provided a proper codon-anticodon interaction was possible with tRNA(Sec). This indicates that none of the three termination codons can function as efficient translational stop signals in that particular mRNA position. The discrimination of the selenocysteine 'sense' codon from a regular stop codon has previously been shown to be dependent on an RNA secondary structure immediately 3' of the UGA codon in the fdhF mRNA. It is demonstrated here that the correct folding of this structure as well as the existence of primary sequence elements located within the loop portion at an appropriate distance to the UGA codon are absolutely required. A recognition sequence can be defined which mediates specific translation of a particular codon inside an mRNA with selenocysteine and a model is proposed in which translation factor SELB interacts with this recognition sequence, thus forming a quaternary complex at the mRNA together with GTP and selenocysteyl-tRNA(Sec).

Variations of lipid profile in animals caused by adenosine analogs: N6 (amido-3-propyl) adenosine hydrochloride and (carboxamido-3-propylamino)-6-(triproprionyl) 2',3',5'beta (D-ribosyl)-9-purine

N6-substituted adenosine analogues are powerful inhibitors of lipolysis in the adipose tissues of animals and humans, because of their agonist effect on A1 purine receptors. Using a model of hypertriglyceridemia provoked by intravenous injection of Triton WR 1339, we observed that Agr 529 [N6(amido-3-propyl)adenosine hydrochloride] at 2 mg.kg-1 intravenous in rabbits, and intraperitoneally and orally in rats led to a return of the levels of circulating triglycerides to normal values. In addition, Agr 529 and its prodrug, Agr 540 [(carboxamido-3-propylamino)-6-(triproprionyl)2', 3',5'beta(D-ribosyl)-9-purine] administered to rats at 3 and 30 mg.kg-1, respectively, returned plasma triglyceride concentrations to normal levels. Intravenous administration of Agr 529 to normal rats led to decreased concentrations of plasma fatty acids, phospholipids, triglycerides and total cholesterol as a function of dose. The decrease began at 0.1 mg.kg-1 and was highly significant at 3 mg.kg-1. In the same conditions, the intraperitoneal administration of Agr 529 caused a dose-dependent hypolipemia. There was no apparent effect on cholesterol and on the triglycerides of high density lipoproteins. A kinetic study showed that the antilipemic effect of Agr 529 intravenously injected at 3 mg.kg-1 began 30 minutes after the injection with a maximum effect at 2 hours. The effect persisted up to 8 hours after injection. The present results show that the administration of Agr 529 and Agr 540 to normal animals causes hypolipemia (decrease in fatty acids, phospholipids, triglycerides and cholesterol) and restores induced hypertriglyceridemia. These effects may be attributed to an interaction of the molecules with A1 purinergic receptors of adipose tissue.

The family of the asthmatic child

The authors report clinical study of 34 asthmatic children between the ages of ten and 15, followed at a specialized outpatient clinic of a large pediatric hospital in Montreal. Evaluation of the children and their families involved the use of clinical scores with inter-rater agreement. The study found strong associations between certain personality traits and an excessive use of medication, and between personality traits and family structure. Regardless of the severity of their asthma, children with high levels of anxiety and dependence were more likely to live with highly cohesive families and to use greater quantities of cortisone than children with better adapted personality structures. Pathological family settings are known to cause more emotional and behaviour problems in children. We suggest there is a reciprocal influence, and we consider the effects on the family of an early childhood disease that is persistent, worrisome, unpredictable, and necessitates repeated hospitalization. Prospective studies of the high-risk subgroups identified in this study could facilitate early intervention for asthmatic children and their families.

Absence of correlation between graft-versus-host associated immunosuppression and cytotoxic T cell activity in response to major histocompatibility antigens

Studies in mice suggest that the T cell subset involved in graft-versus-host-reaction (GvHR) across the major histocompatibility complex (MHC) depends on the class of MHC antigens recognized by the donor cells. However, the correlation between phenotype and function is not absolute. Using a functional approach, we investigated in a parent --> F1 hybrid model differing at the whole MHC, whether graft-versus-host (GvH) associated immunosuppression was correlated with donor cytotoxic T cell activity. The immunodeficiency was tested by the ability of the F1 mice to generate a cytotoxic T cell response against trinitrophenyl-modified syngeic cells (TNF-self) or an alloantigen. F1 specific parental cytotoxic T cells, generated in vitro, induced less immunosuppression than naive parental cells. Specific in vivo priming increased the cytotoxicity of parental spleen cells, but decreased their capacity to induce GvH-associated immunosuppression. In contrast, nonspecific priming resulted in the usual immunodeficiency. In conclusion, there was no correlation between GvH-associated immunosuppression and cytotoxic T cell activity of the parental cells.

Selenoprotein synthesis: an expansion of the genetic code

A number of enzymes employ the unusual amino acid selenocysteine as part of their active site because of its high chemical reactivity. Selenocysteine is incorporated into these proteins co-translationally: biosynthesis occurs on a specific tRNA and insertion into a growing polypeptide is directed by a UGA codon in the mRNA. In E. coli, this requires a specific translation factor. Selenocysteine thus represents a unique expansion of the genetic code.

Nitrate-inducible formate dehydrogenase in Escherichia coli K-12. II. Evidence that a mRNA stem-loop structure is essential for decoding opal (UGA) as selenocysteine

fdnG, encoding the selenopeptide of Escherichia coli formate dehydrogenase-N, contains an in-frame opal (UGA) codon at amino acid position 196 that directs selenocysteine incorporation. We have identified sequences that contribute to the mRNA context required for decoding this UGA as selenocysteine. We identified a potential stem-loop structure immediately downstream of UGA196 that is comparable in size and structure to a stem-loop predicted to form in fdhF, which encodes the selenopeptide of E. coli formate dehydrogenase-H. Mutational analysis of the fdnG stem-loop structure suggests that it is critical for decoding UGA196 as selenocysteine. Our data indicate that both stability and specific nucleotide sequences of the stem-loop likely contribute to the appropriate mRNA context for selenocysteine incorporation into the fdnG gene product.

The length of the aminoacyl-acceptor stem of the selenocysteine-specific tRNA(Sec) of Escherichia coli is the determinant for binding to elongation factors SELB or Tu

Mutations in selC, which reduce the 8-base pair aminoacyl-acceptor helix to the canonical 7-base pair length (tRNA(Sec)(delAc] or which replace the extra arm of tRNA(Sec) by that of a serine acceptor tRNA species (tRNA(Sec)(ExS), block the function in selenoprotein synthesis in vivo (Baron, C., Heider, J., and Böck, A. (1990) Nucleic Acids Res. 18, 6761-6766). tRNA(Sec), tRNA(Sec)(delAc), and tRNA(Sec)(ExS) were purified and analyzed for their interaction with purified seryl-tRNA synthetase, selenocysteine synthase and translation factors SELB and EF-Tu. It was found that seryl-tRNA synthetase displays 10-fold impaired Km and Kcat values for tRNA(Sec) in comparison to tRNA(Ser), decreasing the overall charging efficiency (Kcat/Km) of tRNA(Sec) to 1% of that characteristic for tRNA(Ser). tRNA(Sec)(ExS) was a less efficient substrate for the enzyme (Kcat/Km 0.2% of the tRNA(Ser) value) whereas the tRNA(Ser)(delAc) variant was charged with an approximately 2-3-fold improved rate compared to wild-type tRNA(Sec). Both mutant tRNA variants, when charged with L-serine, were able to interact with selenocysteine synthase to give rise to selenocysteyl-tRNA with tRNA(Sec)(ExS) being as efficient as wild-type tRNA(Sec). Seryl-tRNA(Sec)(delAc), on the other hand, was selenylated very slowly. Reduction of the length of the aminoacyl-acceptor stem to 7 base pairs prevented the interaction with translation factor SELB but allowed binding to EF-Tu, irrespective of whether tRNA(Sec)(delAc) was charged with serine or selenocysteine. The aminoacyl-acceptor helix of tRNA(Sec), therefore, is a major determinant directing binding to SELB and precluding interaction with EF-Tu.

Mutagenesis of selC, the gene for the selenocysteine-inserting tRNA-species in E. coli: effects on in vivo function

The selenocysteine-inserting tRNA (tRNA(Sec)) of E. coli differs in a number of structural features from all other elongator tRNA species. To analyse the functional implications of the deviations from the consensus, these positions have been reverted to the canonical configuration. The following results were obtained: (i) inversion of the purine/pyrimidine pair at position 11/24 and change of the purine at position 8 into the universally conserved U had no functional consequence whereas replacements of U9 by G9 and of U14 by A14 decreased the efficiency of selenocysteine insertion as measured by translation of the fdhF message; (ii) deleting one basepair in the aminoacyl acceptor stem, thus creating the canonical 7 bp configuration, inactivated tRNA(Sec); (iii) replacement of the extra arm by that of a serine-inserting tRNA abolished the activity whereas reduction by 1 base or the insertion of three bases partially reduced function; (iv) change of the anticodon to that of a serine inserter abolished the capacity to decode UGA140 whereas the alteration to a cysteine codon permitted 30% read-through. However, the variant with the serine-specific anticodon efficiently inserted selenocysteine into a gene product when the UGA140 of the fdhF mRNA was replaced by a serine codon (UCA). Significantly, none of these changes resulted in the non-specific incorporation of selenocysteine into protein, indicating that the mRNA context also plays a major role in directing insertion. Taken together, the results demonstrate that the 8-basepair acceptor stem and the long extra arm are crucial determinants of tRNA(Sec) which enable decoding of UGA140 in the fdhF message.

Accumulation of bromodeoxyuridine-labeled cells in central and peripheral lymphoid organs: minimal estimates of production and turnover rates of mature lymphocytes

Daily lymphocyte production in both central and peripheral lymphoid organs was evaluated by associating in vivo incorporation of bromodeoxyuridine (BrdUrd) with cell surface labeling and multi-parameter flow analysis. At least 10% of mature T and B lymphocytes are generated every 24 h. The kinetic behavior of these cell populations differs, however, in that mature B cells are generated predominantly in the precursor compartments of the bone marrow, while most mature T cell generation occurs at the periphery. Therefore, peripheral expansion is the major mechanism of mature T cell production in the adult mouse. By following the accumulation of BrdUrd-labeled cells in peripheral lymphoid organs we found that the progeny of the daily lymphocyte production was sufficient to renew 30%-40% of all peripheral T and B cells every 48 h, demonstrating a high turnover rate of mature lymphocytes. We also examined the conditions of BrdUrd labeling of cycling cells in vivo. We found that while greater than 90% of bone marrow and thymus cells in S phase were labeled with a single injection of BrdUrd, in peripheral lymphoid compartments 70% of T and B cells in S failed to incorporate BrdUrd. Particular schedules of BrdUrd administration were required to overcome the low labeling efficiency of mature cells in vivo. Prolonged BrdUrd administration, however, had toxic effects on resident cells. The low labeling efficiency of BrdUrd incorporation by mature cells, as well as its potential toxicity during prolonged administration, may explain controversial results obtained by the different strategies used to study lymphocyte population dynamics.

Study of the thymocyte cell cycle by bivariate analysis of incorporated bromodeoxyuridine and DNA content

The in vivo cell cycle of normal murine thymocytes was studied by bivariate analysis of bromodeoxyuridine and total DNA content in the 24 h following a single injection of the thymidine analogue. Bromodeoxyuridine incorporation was strictly limited to cells in S phase and 98% of S phase cells were labeled, demonstrating high efficiency and specificity. Cell-cycle parameters were determined by measuring the DNA content of bromodeoxyuridine-labeled cells, related to their distribution in the different phases. The changes of this distribution as a function of time reflected the progression of the cells along the cell cycle. The duration of total cycle, S phase, and both G2/M and G1 was 10 h, 6.5 h and 1.5 h, respectively. All thymocytes labeled in S phase entered G2/M, divided and returned to the G0/G1. Seventy percent of them remained in the resting state, and the other 30% re-entered a second S phase. Cell-cycle parameters of isolated CD4-CD8- cells were also determined. No evidence of cell loss during S or G2/M phase was found, suggesting that intrathymic cell death is not directly linked to the proliferative phases of differentiation.

Changes in plasma catecholamine levels after the intraperitoneal and intracerebroventricular administration of adenosine analogues and of clonidine in conscious rats

When an adenosine analogue, N6-(amido-3-propyl) adenosine hydrochloride (Agr 529) is administered systemically, it causes a substantial release of epinephrine (E) by the adrenal medulla with no change in plasma norepinephrine (NE) levels. Low doses of N6-R-phenylisopropyl adenosine (L-PIA), an agonist of adenosine A1 receptors, has no significant effect on plasma epinephrine levels, which are increased by high doses of the analogue. Low doses of 5'-N-ethylcarboxamido-adenosine (NECA), an agonist of adenosine A2 receptors, however, lead to increases. The intracerebroventricular (icv) administration of Agr 529 leads to a significant decrease in plasma NE without affecting E levels. This action is synergistic with that of clonidine icv. The mechanism of central action of this effect is discussed. It can be admitted that the inhibitory effect of adenosine analogues icv occurs via an inhibition of the posterolateral hypothalamus and the locus coeruleus, although we cannot rule out an action on more rostral-situated brain regions. The authors suggest that the central effect of Agr 529 results primarily from the inhibition of central acetylcholine release caused by adenosine analogues and review experimental arguments enabling this hypothesis to be supported. On the other hand, the considerable release of plasma epinephrine seen when adenosine analogues are administered systemically can be attributed to their stimulation of ACTH secretion by the pituitary and the increase in glucocorticoids in the adrenal medulla, as a result of the existence of the cortico-medullary portal system. These glucocorticoids stimulate phenylethanolamine-N-methyltransferase, which transforms norepinephrine to epinephrine.

A multicenter, double-blind, placebo-controlled trial of the efficacy of prazosin in the treatment of dysuria associated with benign prostatic hypertrophy

An 8-center, double-blind, placebo-controlled trial of 39 patients with benign prostatic hypertrophy was conducted to assess the effects of prazosin HCl treatment on functional urologic variables after a treatment period of 4 weeks. The randomized groups were comparable for demographic variables and symptoms, except for the mean residual urinary volume, which was significantly higher in the prazosin HCl group. Prazosin HCl elicited statistically significant improvements in the mean prostatic urethral pressure and prostate area (Mann-Whitney U test: p = 0.001 for both variables as compared with the placebo group). Functional bladder capacity also improved significantly in the group receiving the test drug (Mann-Whitney U test: p = 0.05, as compared with the placebo group). Clinical improvements were also observed in the mean maximum urinary flow, decreased nocturia frequency, and residual urinary volume. Patient preference significantly favored the prazosin HCl treatment (Mann-Whitney U test: p = 0.001). Seven patients on prazosin HCl and 5 receiving placebo reported one or more side effects during the trial phase; these were mild to moderate and disappeared or were tolerated. No statistically significant effects on blood pressure or heart rate were observed.

Phosphoinositide metabolism and metabolism-contraction coupling in rabbit aorta

We tested a hypothesis that metabolism-contraction coupling in vascular smooth muscle is controlled by the rate of delivery of energy to ATP-dependent reactions in the inositol phospholipid transduction system that generate second messengers exerting control on smooth muscle force. Rabbit aorta was contracted by norepinephrine (NOR) under conditions of normoxia and hypoxia (bath PO2 less than 40 mmHg), and changes in inositol phospholipid pool sizes and metabolic flux rates (JF) were determined. JF was determined by labeling free cytosolic myo-inositol by incubation of unstimulated muscle with myo-[3H]inositol and then measuring rates of incorporation of this isotope into inositol phospholipids and inositol phosphates when the muscle was activated by NOR. JF measured during maintenance of NOR-induced force was markedly inhibited during hypoxia to 40-50% of that determined during normoxia; rates of increases in inositol phosphate radioactivities were similarly depressed during NOR activation under hypoxia. The hypoxia-induced decrease in JF was associated with four- to fivefold increase in phosphatidylinositol 4-phosphate (PIP) total pool size, suggesting PIP kinase was inhibited and rate limiting. Total pool sizes of phosphatidylinositol, phosphatidylinositol bisphosphate, and phosphatidic acid were unchanged from values seen during activation under normoxia. These data suggest that activation of inositol phospholipid metabolism, which generates inositol 1,4,5-trisphosphate (IP3) and diacylglycerol, is blunted under conditions where aerobic energy production is inhibited. Data are consistent with "rate-limiting" effects of decreased ATP delivery, or decreased phosphate potential, on PIP kinase and reactions that control resynthesis of phosphatidylinositol.