High oxygen delivery and extraction by perfluorocarbon-primed extracorporeal membrane oxygenation do not prevent anaerobic metabolism in rabbits

PURPOSE

This study was designed to evaluate the advantage of perfluorocarbon (PFC) emulsion priming for venoarterial extracorporeal membrane oxygenation (ECMO) by comparison with hydroxyethyl starch (HES) solution in rabbits (2.8 to 3.9 kg).

RESULTS

ECMO initiation was accompanied by a profound decrease in hematocrit (from 40.1% to 14.9%) in both groups. The arterial and the right atrial oxygen contents in the PFC group (n = 4; 38.5 and 11.5 mL/dL) were greater than in the HES group (n = 5; 7.0 and 5.1 mL/dL). Right atrial oxygen tension in the PFC group increased at the beginning of ECMO (from 38.4 to 51.2 mm Hg; P = .031) and remained higher than in the HES group for 60 minutes. These results indicate that oxygen supply and extraction in the PFC group were much greater than in the HES group. However, plasma lactate increased progressively during the 120-minute ECMO procedure in both groups (from 1.8 to 14.5 in the HES group, and from 2.3 to 12.2 in the PFC group).

CONCLUSION

Perfluorocarbon priming for ECMO, although providing high oxygen delivery and extraction, does not prevent anaerobic metabolism.

HIV-1 Nef binding protein expressed on the surface of murine blood cells

The Nef protein of HIV-1 binds to and induces apoptotic cytolysis of a broad spectrum of uninfected blood cells of humans and mice independently of CD95 (Fas). A 24-kDa glycoprotein responsible for Nef binding and the Nef-induced apoptosis has been identified on the surface of human CD4+ T cells. Using mouse monoclonal antibodies (mAbs) against the human Nef-binding protein and flow cytometry, we analyzed the expression of a corresponding protein on murine cells. The mAbs were shown to bind to the surface of various murine cell lines including T and B lymphocytes and macrophages, in a fashion similar to the binding by soluble Nef protein. The mAbs competed with the Nef protein in binding to the cell surfaces. Immunoprecipitation of cell membranes revealed a 25-kDa protein recognized by the mAbs. Treatment of the soluble Nef protein with anti-Nef (C terminus) mAb, but not anti-Nef (N terminus) mAb, deprived the Nef of the cell binding activity, indicating that binding site is located in the C-terminal domain. Cross-linking of the cell-bound mAbs with secondary antibodies induced apoptotic cytolysis, which occurred independently of CD95 (Fas). On the other hand, neither the mAbs nor the soluble Nef protein reacted with primary lymphocytes in a resting stage obtained from lymph nodes, thymus and spleen of 5-week-old mice. However, some of the cells, predominantly comprising CD4+ T cells, became positive for the both reactions after mitogenic stimulation with phytohemagglutinin, concanavalin A or lipopolysaccharide of Escherichia coli. These results suggest that the 25-kDa protein on murine cell surfaces corresponds to the human Nef binding protein and is responsible for the Nef-induced apoptosis, and that its expression on the cell surface depends on cellular activation.

Inhibition of HIV-1 Nef-induced apoptosis of uninfected human blood cells by serine/threonine protein kinase inhibitors, fasudil hydrochloride and M3

The Nef protein of HIV-1 binds to and induces apoptotic cytolysis of uninfected but activated human peripheral blood mononuclear cells (PBMC) and various cell line cells derived from CD4+ T, CD8+ T and B lymphocytes, macrophages, and neutrophils. The Nef-induced apoptosis also occurs with blood cells not expressing CD95 (Fas). The Nef-induced apoptosis as well as Fas-mediated apoptosis was inhibited by acetyl-Try-Val-Ala-Asp-CHO, an IL-1beta converting enzyme (ICE) inhibitor. On the other hand, serine/threonine protein kinase (PK) inhibitors, H-7, fasudil hydrochloride and M3, inhibited the Nef-induced apoptosis, and not the Fas-mediated one, without affecting the cell-binding activity of Nef and Nef-binding capacity of the activated cells. Preincubation of the cells with the drugs before being bound by Nef was required for the inhibition of apoptosis. These results suggest that the PK inhibitors specifically act on a cellular protein involved in the upper stream of signal transduction pathway of the Nef-induced apoptosis, which is different from the Fas-mediated pathway but meets it upstream of ICE. In addition, the drugs suppressed the cellular activation-associated cell surface expression of a putative Nef-binding protein in PBMC, although they had no influence on its expression in cell line cells. These findings suggest the feasibility of clinical use of the PK inhibitors to prevent the development of AIDS by inhibiting the Nef-induced apoptosis of uninfected blood cells.

Basal intracellular free Mg2+ concentration in smooth muscle cells of guinea pig tenia cecum: intracellular calibration of the fluorescent indicator furaptra

Longitudinal muscle strips dissected from tenia cecum of guinea pig were loaded with the Mg2+ indicator, furaptra, and the relation between the fluorescent ratio signal (R) and cytoplasmic free Mg2+ concentration ([Mg2+]i) was studied in smooth muscle cells at 25 degrees C. After the application of ionophores (4-bromo-A23187, monensin, and nigericin), a small immediate offset of R (deltaRjump) was followed by a slow change in R (deltaRslow), which reached a steady level within 2-5 h. The deltaRjump was independent of Mg2+ concentration in solution ([Mg2+]o), and was thought to be unrelated to the change in [Mg2+]i. The direction of the deltaRslow depended on [Mg2+]o with a reversal at approximately 1 mM [Mg2+]o. The intracellular calibration curve was constructed from the steady levels of deltaRslow, and the dissociation constant was 5.4 mM. With the intracellular calibration curve and correction for the deltaRjump, basal [Mg2+], was estimated to be 0.98 +/- 0.05 mM (mean +/- SE, n = 12). When the same calibration was applied to A7r5 cells and rat ventricular myocytes, estimates of basal [Mg2+]i of these cells were 0.74 +/- 0.02 mM (n = 33) and 1.13 +/- 0.06 mM (n = 9), respectively. These results suggest that the basal [Mg2+] level is approximately 1 mM at least in some types of smooth muscle cells, as generally found in striated muscles.

Determinants of organ tropism of Sendai virus

Wild-type Sendai virus is exclusively pneumotropic in mice. Protease activation mutants, ts-f1 and F1-R, were isolated from persistently infected tissue culture cells. Additional mutants were isolated from wild-type Sendai virus with phenotypes similar to the pantropic mutant, F1-R. The genome of the mutants was sequenced and mutations were revealed in several proteins encoded by the genes. Three of the six mutations in the fusion (F) proteins were considered prime candidates for the determinant of pantropism. Characterization of the mutants led to the finding that the exchange (Ser to Pro) residue 115 next to the cleavage site of the F protein was the primary determinant that resulted in the enhanced cleavability of the F protein. Another important finding was bipolar budding of F1-R in polarized epithelial cells and mouse bronchial epithelium. This has been attributed to two mutations in the matrix (M) protein, at residues 128 (Asp to Gly) and 210 (Ile to Thr). Thus, the determinants of pantropism of F1-R are protease activation of the F protein and biopolar budding attributed to the mutated M protein.

Na+ gradient-dependent Mg2+ transport in smooth muscle cells of guinea pig tenia cecum

Thin strips of guinea pig tenia cecum were loaded with the Mg2+ indicator furaptra, and the indicator fluorescence signals measured in Ca2+-free condition were converted to cytoplasmic-free Mg2+ concentration ([Mg2+]i). Lowering the extracellular Na+ concentration ([Na+]o) caused a reversible increase in [Mg2+]i, consistent with the inhibition of Na+ gradient-dependent extrusion of cellular Mg2+ (Na+-Mg2+ exchange). Curve-fitting analysis indicated that the relation between [Na+]o and the rate of rise in [Mg2+], had a Hill coefficient of approximately 3, a [Na+]o at the half-maximal rate of rise of approximately 30 mM, and a maximal rate of 0.16 +/- 0.01 microM/s (mean +/- SE, n = 6). Depolarization with 56 mM K+ shifted the curve slightly toward higher [Na+]o without significantly changing the maximal rate, suggesting that the Na+-Mg2+ exchange was inhibited by depolarization. The maximal rate would correspond to a flux of 0.15-0.4 pmol/cm2/s, if cytoplasmic Mg2+ buffering power (defined as the ratio of the changes in total Mg2+ and free Mg2+ concentrations) is assumed to be 2-5. Ouabain (1-5 microM) increased the intracellular Na+ concentration, as assessed with fluorescence of SBFI (sodium-binding benzofuran isophthalate, a Na+ indicator), and elevated [Mg2+]i. In ouabain-treated preparations, removal of extracellular Na+ rapidly increased [Mg2+]i, with an initial rate of rise roughly proportional to the degree of the Mg2+ load, and, probably, to the Na+ load caused by ouabain. The enhanced rate of rise in [Mg2+]i (up to approximately 1 microM/s) could be attributed to the Mg2+ influx as a result of the reversed Na+-Mg2+ exchange. Our results support the presence of a reversible and possibly electrogenic Na+-Mg2+ exchange in the smooth muscle cells of tenia cecum.

Nef protein of HIV-1 induces apoptotic cytolysis of murine lymphoid cells independently of CD95 (Fas) and its suppression by serine/threonine protein kinase inhibitors

The Nef protein of HIV-1 is suggested to play a role in depletion of uninfected CD4+ T cells leading to the development of AIDS. The recombinant soluble Nef protein was shown to bind to cell surfaces of various murine lymphoid cell lines, including T and B lymphocytes, mastocytoma cells and macrophages. Cross-linking of the cell-bound Nef protein with anti-Nef antibodies induced apoptotic cytolysis of the cells. Although primary lymphocytes from young mice resisted Nef binding and Nef-induced cytolysis, treatment of the cells with concanavalin A or phytohemagglutinin made them susceptible to these activities, indicating that cellular activation is required for the apoptosis. The Nef-induced apoptosis also occurred with murine cells not expressing CD95 (Fas). These findings were quite similar to those obtained for human blood cells, suggesting that the mouse is applicable for analysis of Nef activities. The Nef-induced apoptosis was efficiently suppressed by serine/threonine protein kinase inhibitors, H7, fasudil hydrochloride and M3, which did not inhibit CD95 (Fas)-mediated apoptosis. On the other hand, bisindolylmaleimide, a protein kinase C inhibitor which inhibits CD95 (Fas)-mediated apoptosis, did not affect Nef-induced apoptosis. These results suggest that the Nef-induced apoptosis of murine cells involved a serine/threonine protein kinase-dependent signal transduction pathway distinct from the CD95 (Fas)-mediated system.

High-resolution solution NMR structure of the Z domain of staphylococcal protein A

Staphylococcal protein A (SpA) is a cell-wall-bound pathogenicity factor from the bacterium Staphylococcus aureus. Because of their small size and immunoglobulin (IgG)-binding activities, domains of protein A are targets for protein engineering efforts and for the development of computational approaches for de novo protein folding. The NMR solution structure of an engineered IgG-binding domain of SpA, the Z domain (an analog of the B domain of SpA), has been determined by simulated annealing with restrained molecular dynamics on the basis of 671 conformational constraints. The Z domain contains three well-defined alpha-helices corresponding to polypeptide segments Lys7 to Leu17 (helix 1), Glu24 to Asp36 (helix 2), and Ser41 to Ala54 (helix 3). A family of ten conformers representing the solution structure of the Z domain was computed by simulated annealing of restrained molecular dynamics using the program CONGEN. The average of the root-mean-square deviations (r.m. s.d.) of the individual NMR conformers, relative to the mean coordinates, for the backbone atoms N, Calpha and C' of residues Phe5 through Ala56 is 0.69 A; the corresponding backbone r.m.s.d. for the three-helical core is 0.44 A. Helices 1, 2 and 3 are antiparallel in orientation (Omega12=-170(+/-4) degrees , Omega13=+16(+/-3) degrees , Omega23=+173(+/-7) degrees ). A comparison of backbone amide hydrogen/deuterium exchange rates in free and IgG-bound Z domains demonstrates that the amide protons of helices 1, 2 and 3 are protected from rapid exchange in both states, indicating that all three helices are also intact in the IgG-bound state. These solution NMR results differ from the previously determined X-ray structure of the similar SpA B domain in complex with the Fc fragment of a human IgG antibody, where helix 3 is not observed in the electron density map and from the solution NMR structure of the B domain, where helix 3 is observed but helix 1 is tilted by approximately 30 degrees with respect to helices 2 and 3. Hydrogen-bonded N-cap and C-cap formation is observed for all three helices of the Z domain; these capping interactions appear to be highly conserved in the five homologous domains of SpA.

Detection of Borna disease virus genome in normal human brain tissue

Borna disease virus (BDV), a neurotropic virus naturally infecting horses and sheep, has been suggested to be associated with human psychiatric disorders. Thus far no extensive studies have been done, providing the evidence of BDV genome in normal human brain tissue. We therefore examined four brain regions of 30 normal autopsy brains for BDV p24 genome. By highly sensitive nested reverse transcriptase (RT)-mediated PCR analysis, we found positive PCR products in two brains: one in frontal and temporal cortices and hippocampus and another in frontal cortex and olfactory bulb. Our results suggest that BDV can infect human brain tissue latently, without causing an apparent neuropsychiatric disorder.

[The role of cleavage activation of the hemagglutinin by host and bacterial proteases in the induction of the pathogenesis of influenza viruses]

Infectivity and pathogenicity of influenza viruses are based on the interplay between the viral glycoprotein hemagglutinin (HA) and appropriate host proteases. HA receives its full biological activities by proteolytic cleavage of a precursor molecule at a definite cleavage site. Tryptase Clara, an arginine-specific protease secreted by the Clara cells in the bronchial epithelia, is a principal host protease responsible for the cleavage activation and pathogenicity of influenza viruses. Although influenza in normal individuals is usually confined to the upper respiratory tract, the infection often develops into fatal pneumonia in patients with chronic lung diseases, where bacterial infections often occur. Synergistic effects of bacterial infections on the pathogenesis of influenza viruses are described in regard to the cleavage activation of HA.

HIV-1 Nef protein-induced apoptotic cytolysis of a broad spectrum of uninfected human blood cells independently of CD95(Fas)

The Nef protein of HIV-1 binds to uninfected CD4+T lymphocytes and induces apoptotic cytolysis of the cells. We examined several human blood cell lines and peripheral blood mononuclear cells (PBMCs) for Nef-induced apoptotic cell death. Soluble Nef protein was shown to bind to the cell surface of not only CD4+T cells but also CD8+T lymphocytes, B lymphocytes, macrophages and neutrophils. PBMCs from normal subjects resisted Nef binding, and activation of the cells with phytohemagglutinin or concanavalin A converted the cells to be susceptible to the binding. Cross-linking of the Nef proteins bound to the cell surfaces with anti-Nef antibody-induced apoptotic cytolysis of the cells. The Nef-mediated apoptosis occurred independently of CD95(Fas). These results suggest that soluble Nef protein, which is found in sera of HIV-1 infected patients, is involved in the destruction of a broad spectrum of uninfected blood cells leading to immune suppression.

A reverse-type sandwich enzyme-linked immunosorbent assay for detecting antibodies to Borna disease virus

To investigate whether there is an epidemiological correlation between Borna disease virus (BDV) infection and human neuropsychiatric diseases, we established a reverse-type sandwich enzyme-linked immunosorbent assay (RS-ELISA) for detecting specific antibodies to BDV. In this assay, microplate wells were coated dispersely with BDV p40 antigen, followed by the addition of test samples at a low dilution and then the biotinylated p40. A preformed complex of streptavidin and horseradish peroxidase-conjugated biotin and an enzyme substrate were used to measure the captured biotinylated p40. Theoretically, RS-ELISA should specifically detect anti-BDV antibodies without nonspecific signals; such signals possibly occur in conventional serological assays. Additionally, the RS-ELISA could be applied under the same protocols to test samples from a variety of animals. By using anti-BDV rat and rabbit sera, the assay was standardized so that it had high specificity and sensitivity. When we used the RS-ELISA to determine the presence of anti-BDV antibodies in plasma from 70 patients with chronic schizophrenia as well as 40 healthy individuals in the Tokyo area of Japan, no plasma sample was found to possess specific antibodies to BDV p40, indicating no association between BDV infection and the disease in our testing population. A negative reaction was also shown for the sera that had previously been judged to be seropositive for BDV by an immunofluorescence or immunoblot test. These findings suggested that false-positive cases of infection due to nonspecific reactions may be included in previous seroepidemiological information with regard to BDV.

Automated analysis of protein NMR assignments using methods from artificial intelligence

An expert system for determining resonance assignments from NMR spectra of proteins is described. Given the amino acid sequence, a two-dimensional 15N-1H heteronuclear correlation spectrum and seven to eight three-dimensional triple-resonance NMR spectra for seven proteins, AUTOASSIGN obtained an average of 98% of sequence-specific spin-system assignments with an error rate of less than 0.5%. Execution times on a Sparc 10 workstation varied from 16 seconds for smaller proteins with simple spectra to one to nine minutes for medium size proteins exhibiting numerous extra spin systems attributed to conformational isomerization. AUTOASSIGN combines symbolic constraint satisfaction methods with a domain-specific knowledge base to exploit the logical structure of the sequential assignment problem, the specific features of the various NMR experiments, and the expected chemical shift frequencies of different amino acids. The current implementation specializes in the analysis of data derived from the most sensitive of the currently available triple-resonance experiments. Potential extensions of the system for analysis of additional types of protein NMR data are also discussed.

Identification of reactive site of a proteinaceous metalloproteinase inhibitor from Streptomyces nigrescens TK-23

Streptomyces metalloproteinase inhibitor (SMPI), isolated from Streptomyces nigrescens TK-23, is a small proteinaceous metalloproteinase inhibitor consisting of 102 amino acid residues and two disulfide bridges. SMPI specifically inhibits metalloproteinases such as thermolysin. After prolonged incubation with a catalytic amount of thermolysin, it is cleaved at Cys64-Val65 [Murai, H., Hara, S., Ikenaka, T., Oda, K., and Murao, S. (1985) J. Biochem. 97, 173-180]. Hence, for identification of the reactive site, mutants were constructed by substituting Val65 with various amino acid residues (Leu, Ile, Phe, Tyr, Gly, Ser, Lys, and Glu). The mutants were analyzed for inhibitory activity. Among them, V65I, V65L, V65F, and V65Y retained strong inhibitory activity, whereas V65S, V65G, V65K, and V65E showed very weak inhibitory activity against thermolysin. The Ki values were found to be of the order of 10(10) M by using a fluorogenic substrate, MOCAc-Pro-Leu-Gly-Leu-A2pr(Dnp)-Ala-Arg-NH2. In addition, susceptibility to enzyme degradation was analyzed by means of limited proteolysis with thermolysin. Mutants which retained strong inhibitory activity were cleaved by thermolysin only at the reactive site, in the same way as native SMPI. The mutants which showed weak inhibitory activity underwent rapid degradation. These results were consistent with the substrate specificity of thermolysin. Based on these results, the reactive site of SMPI was identified as Cys64-Val65.

Segment-specific noncoding sequences of the influenza virus genome RNA are involved in the specific competition between defective interfering RNA and its progenitor RNA segment at the virion assembly step

The generation of influenza A virus defective interfering (DI) particles was studied by using an NS2 mutant which produces, in a single cycle of virus replication, a large amount of DI particles lacking the PA polymerase gene. The decrease in PA gene replication has been shown to occur primarily at the cRNA synthesis step, with preferential amplification of PA DI RNA species present in a marginal amount in the virus stock. In addition, at the assembly step the PA DI RNAs were preferentially incorporated into virions, resulting in selective reduction in the packaging of the PA gene into virions. Similarly, in cells dually infected with the NS2 mutant and wild-type viruses, packaging of the wild-type PA gene was also greatly suppressed. In contrast, incorporation of other RNA segments, i.e., the PB2 and NS genes, was not affected, suggesting that the PA DI RNAs competed only with the PA gene in a segment-specific manner. Experiments involving rescue of recombinant chloramphenicol acetyltransferase (CAT) RNA flanked by the noncoding regions of the PA (PA/CAT RNA) and PB2 (PB2/CAT RNA) genes into viral particles showed that only PA/CAT RNA was not rescued by infection with the NS2 mutant virus containing the PA DI RNAs. However, recombinant PA/CAT RNA in which either the 3' or 5' noncoding region was replaced with that of the PB2 gene was rescued by the NS2 mutant. These results suggest that the noncoding regions of the PA gene are responsible for the competition with PA DI RNA species at the virus assembly step and that coexistence of the both noncoding regions would be a prerequisite for this phenomenon. Decreased packaging of the progenitor RNA by the DI RNA, in addition to the suppression of cRNA synthesis, is likely involved in the production of DI particles.

Increased secretion of TNF-alpha by costimulation of mast cells via CD28 and Fc epsilon RI

The present study unequivocally demonstrated the expression of CD28 on murine bone marrow-derived cultured mast cells and a mast cell line, MCP-5. Stimulation of surface CD28 molecules on mast cells with anti-CD28 mAbs induced tyrosine phosphorylation of cellular proteins, including several protein tyrosine kinases and their substrates, such as Itk/Emt (Emt), Btk, Syk, c-Cbl, Shc, and Vav. CD28-stimulated tyrosine phosphorylation was followed by a rebound hypophosphorylation. Interestingly, CD28 stimulation alone elicited a low level secretion of TNF-alpha. On the other hand, cross-linking of the high affinity IgE receptor (Fc epsilon RI) on mast cells induces a set of activation events, i.e., degranulation, secretion of eicosanoids, secretion of cytokines, and DNA synthesis. Concurrent stimulation of mast cells through CD28 enhanced Fc epsilon RI-induced TNF-alpha secretion in a dose-dependent manner. Together, the present data suggest a role for CD28-mediated costimulation of mast cells in the initiation and progression of allergic responses and other diseases.

Increased secretion of TNF-alpha by costimulation of mast cells via CD28 and Fc epsilon RI

The present study unequivocally demonstrated the expression of CD28 on murine bone marrow-derived cultured mast cells and a mast cell line, MCP-5. Stimulation of surface CD28 molecules on mast cells with anti-CD28 mAbs induced tyrosine phosphorylation of cellular proteins, including several protein tyrosine kinases and their substrates, such as Itk/Emt (Emt), Btk, Syk, c-Cbl, Shc, and Vav. CD28-stimulated tyrosine phosphorylation was followed by a rebound hypophosphorylation. Interestingly, CD28 stimulation alone elicited a low level secretion of TNF-alpha. On the other hand, cross-linking of the high affinity IgE receptor (Fc epsilon RI) on mast cells induces a set of activation events, i.e., degranulation, secretion of eicosanoids, secretion of cytokines, and DNA synthesis. Concurrent stimulation of mast cells through CD28 enhanced Fc epsilon RI-induced TNF-alpha secretion in a dose-dependent manner. Together, the present data suggest a role for CD28-mediated costimulation of mast cells in the initiation and progression of allergic responses and other diseases.

Human mucus protease inhibitor in airway fluids is a potential defensive compound against infection with influenza A and Sendai viruses

Tryptase Clara, a trypsin-like protease localized exclusively in and secreted from Clara cells to the bronchial epithelium of rat, proteolytically activates the infectivity of influenza A virus [H. Kido, Y. Yokogoshi, K. Sakai, M. Tashiro, Y. Kishino, A. Fukutomi, and N. Katunuma (1992) J. Biol. Chem. 267, 13573-13579]. We report here that human mucus protease inhibitor (MPI), a major inhibitor of granulocyte elastase in the lining fluids of the human respiratory tract, significantly inhibited proteolytic activation of the infectivity of influenza A and Sendai viruses by tryptase Clara in vitro and multi-cycles of mouse-adapted influenza A virus replication in rat lungs in vitro. Recombinant MPI and the C- but not the N-terminal domain of the MPI inhibited both the proteolytic activity of tryptase Clara and the activation of virus infection. The 50% inhibitory concentrations of recombinant MPI and the C-terminal domain for tryptase Clara with Sendai virus envelope glycoprotein as substrate were 7.4 and 61.6 nM, respectively. These results indicate that MPI is a defensive compound against virus infection. Since there is evidence suggesting that concentrations of MPI in respiratory fluids are insufficient for prevention of virus infection, administration of MPI in the airway may be useful for treatment of these virus infections.

Epitope mapping of murine monoclonal antibodies against human immunodeficiency virus type 1 Nef

It has shown that the human immunodeficiency virus type 1 (HIV-1) Nef protein has the high antigenicity in HIV-1 seropostive individuals. We newly obtained seven monoclonal antibodies (mAbs). To identify the antigenic determinants of HIV-1 Nef protein against murine, epitope mapping of the mAbs was performed by enzyme-linked immunosorbent assay (ELISA) by using several recombinant truncated Nef fusion proteins, that were expressed in Esherichia coli, and synthetic peptides. The results showed that mAbs A6, A7, F2, F3, F4, F8 and E5 recognized epitopes on Nef protein located at amino acid residues 18-26, 28-45, 115-137, 128-137, 115-126, 128-137, and 170-181, respectively.

In vitro cytocidal effects of human immunodeficiency virus type 1 Nef on unprimed human CD4+ T cells without MHC restriction

We have previously shown that the C-terminal region of human immunodeficiency virus type 1 (HIV-1) Nef antigen present on the outer surface of virus-infected cells has an affinity for uninfected T cells and that the Nef protein is responsible for T cell death. To exclude completely the possibility of MHC restriction of this cytotoxic activity, the in vitro cytotoxic potential of HIV-1 Nef against various CD4+ T cell lines as well as naive T lymphocytes was investigated using a baculovirus expression system. Insect cells expressing myristoylated Nef on their cell surface were shown to kill a proportion of CD4+ T cells within 8 h. However, N-terminal truncated and unmyristoylated Nef proteins were not present on the outer surface of insect cell membranes and failed to show any killing activity. Monoclonal antibodies against the C-terminal region of Nef inhibited cytolysis. Thus, we conclude that specific Nef-mediated cytolysis is induced by contact with unprimed CD4+ T lymphocytes without MHC restriction.

[Laboratory virological diagnosis of imported dengue cases]

Suspected dengue cases in Japan during the period of 1985-1995, 173 cases with unknown febrile illness entering or returning from mostly southeast Asia, were tested by serology and RT-PCR gene amplification. Seventy seven cases were confirmed by a significant rise of dengue 2 (Den 2) HI antibody in paired sera or by detection of HI antibody titer higher than 1:320 in single serum. The other 3 cases with antibody levels not higher than 1:80 in paired sera and 12 cases with an antibody 1:160 in single sera were positively suspected of dengue infection but were not confirmed. Countries of origin of confirmed cases were Thailand (39 cases), Philippinse (15), India (13), and Indonesia (9). Sera of dengue cases showed high degrees of cross reactivity of Japanese encephalitis virus (JEV) in HI test but not in IgM capture ELISA. Sera of confirmed JEV-infected cases, however, showed practically no cross reactivity to Den 1 4 in HI test, suggesting unilateral cross reactivity of HI antibody. RT-PCR detected the Den 1 genome in sera of 3 cases obtained within 3 days after onset and the Den 2 genome in serum of case 4 days after onset. Although the number is limited, 92 (53%) out of 173 cases of febrile illness of unknown etiology entering Japan from tropical countries were either confirmed or positively suspected to be dengue fever. Considering possibilities of under reporting, importations of tropical viral infections should be bigger in number and will necessitate our intensified alertness.

Clustered localization of oligomeric Nef protein of human immunodeficiency virus type 1 on the cell surface

We studied human immunodeficiency virus type 1 (HIV-1) Nef protein biochemically and histologically. HIV-1 Nef, derived from baculosystem and from cells infected with HIV-1, formed homomeric monomers, dimers, trimers, and further polymers. These oligomers were non-covalently associated. In cells infected with HIV-1, Nef molecules were clustered at the cell surface as well as cytoplasm. Our previous results have indicated that the Nef on the surface of cells infected with HIV-1 is cytotoxic against uninfected CD4+ T cells. Thus, it is very likely that the HIV-1-mediated cytotoxic reaction is due, at least in part, to the clustered localization of oligomeric Nef on the cell surface.

Phase labeling of C-H and C-C spin-system topologies: application in constant-time PFG-CBCA(CO)NH experiments for discriminating amino acid spin-system types

Triple-resonance experiments facilitate the determination of sequence-specific resonance assignments of medium-sized 13C,15N-enriched proteins. Some triple-resonance experiments can also be used to obtain information about amino acid spin-system topologies by proper delay tuning. The constant-time PFG-CBCA(CO)NH experiment allows discrimination between five different groups of amino acids by tuning (phase labeling) independently the delays for proton-carbon refocusing and carbon-carbon constant-time frequency labeling. The proton-carbon refocusing delay allows discrimination of spin-system topologies based on the number of protons attached to C alpha and C beta atoms (i.e. C-H phase labeling). In addition, tuning of the carbon-carbon constant-time frequency-labeling delay discriminates topologies based on the number of carbons directly coupled to C alpha and C beta atoms (i.e. C-C phase labeling). Classifying the spin systems into these five groups facilitates identification of amino acid types, making both manual and automated analysis of assignments easier. The use of this pair of optimally tuned PFG-CBCA(CO)NH experiments for distinguishing five spin-system topologies is demonstrated for the 124-residue bovine pancreatic ribonuclease A protein.

Human immunodeficiency virus type 1 Nef protein on the cell surface is cytocidal for human CD4+ T cells

We have previously shown that the carboxyl-terminal region of human immunodeficiency virus type 1 (HIV-1) Nef antigen present on the outer surface of virus-infected cells has affinity for uninfected T cells. Here, the in vitro cytotoxic potential of HIV-1 Nef on the T cell surface against CD4+ T cells was investigated in detail. Human T cells expressing Nef on the cell surface by transfection with non-infectious mutant HIV-1 proviruses were demonstrated to kill CD4+ T cells efficiently. Furthermore, it was shown that the carboxyl-terminal portion of Nef was cytotoxic for CD4+ T cells and that monoclonal antibody against the carboxyl-terminal region of Nef inhibited Nef induced-cytolysis. Thus, we concluded that Nef protein on CD4+ T cells may play an important role in the specific loss of CD4+ T lymphocytes during HIV-1 infection.

Soluble Nef antigen of HIV-1 is cytotoxic for human CD4+ T cells

We have previously shown that Nef-gene 10 fusion protein induces marked growth arrest of human primary CD4+ T cells. Here, in vitro cytostatic and cytotoxic activities of human immunodeficiency virus type 1 (HIV-1) Nef against CD4+ T cells were extensively investigated. Growth of human CD4+ cells was inhibited significantly just by the addition of purified full-length Nef to cultures. When Nef was cross-linked by anti-Nef antibodies, it became very cytocidal for CD4+ T cells. A high percentage of sera from HIV-1-infected individuals contained soluble Nef. Thus, soluble Nef in vivo may play an important role in immunodysfunction of CD4+ T lymphocytes in HIV-1 infection.