Ion channel expression by white matter glia: I. Type 2 astrocytes and oligodendrocytes

White matter is a compact structure consisting primarily of neuronal axons and glial cells. As in other parts of the nervous system, the function of glial cells in white matter is poorly understood. We have explored the electrophysiological properties of two types of glial cells found predominantly in white matter: type 2 astrocytes and oligodendrocytes. Whole-cells and single-channel patch-clamp techniques were used to study these cell types in postnatal rat optic nerve cultures prepared according to the procedures of Raff et al. (Nature, 303:390-396, 1983b). Type 2 astrocytes in culture exhibit a "neuronal" channel phenotype, expressing at least six distinct ion channel types. With whole-cell recording we observed three inward currents: a voltage-sensitive sodium current qualitatively similar to that found in neurons and both transient and sustained calcium currents. In addition, type 2 astrocytes had two components of outward current: a delayed potassium current which activated at 0 mV and an inactivating calcium-dependent potassium current which activated at -30 mV. Type 2 astrocytes in culture could be induced to fire single regenerative potentials in response to injections of depolarizing current. Single-channel recording demonstrated the presence of an outwardly rectifying chloride channel in both type 2 astrocytes and oligodendrocytes, but this channel could only be observed in excised patches. Oligodendrocytes expressed only one other current: an inwardly rectifying potassium current that is mediated by 30- and 120-pS channels. Because these channels preferentially conduct potassium from outside to inside the cell, and because they are open at the resting potential of the cell, they would be appropriate for removing potassium from the extracellular space; thus it is proposed that oligodendrocytes, besides myelinating axons, play an important role in potassium regulation in white matter. The conductances present in oligodendrocytes suggest a "modulated Boyle and Conway mechanism" of potassium accumulation.     

Regulation of tension on hair-cell transduction channels: displacement and calcium dependence

An epithelial preparation of the bullfrog sacculus was used to characterize the initial rate of the adaptation mechanism in hair cells and its dependence on displacement and calcium. The I(X) curve relating transduction current and bundle displacement shifted along the X-axis without substantial change in slope, as previously observed, suggesting that adaptation involves a change in the attachment point of the elastic element connected to ion channels. If the "tip links" model of transduction is correct, this implies that one end of the link moves along the side of the stereocilium. The rates were highly asymmetric: in the tensioning direction the rate was roughly constant at 1-2 microns/sec (calculated as motion along a stereocilium); this is similar to that of myosin on actin. In the relaxing direction it appeared linearly dependent on tension. Calcium preferentially potentiated the relaxation, and apparently reduced the resting tension in the elastic element. The calcium site appears specific for calcium, as other divalent cations inhibited its action. Dihydrostreptomycin inhibited the positive rate, but its effect could not be explained by a simple channel block, and it seems inconsistent with screening of negative charge in the mouth of the transduction channel.     

HBs-Ag-negative hepatitis in a hemodialysis unit: relation to Epstein-Barr virus.

Eleven of 40 patients in a hemodialysis unit had clinical or biochemical evidence of hepatitis during a five-week period. The clinical disease was mild, being limited solely to dialysis patients. Epidemiologic investigation indicated that the incubation period was between 17 and 35 days and that 10 of 11 patients had been exposed to a single venous-pressure monitor before onset. Dried blood and evidence of blood reflux up the venous-pressure gauge suggested that cross-contamination of the blood of successive patients probably resulted in transmission of disease. No association with the hepatitis B surface antigen or anti-hepatitis B antibody was demonstrated, but 10 of the 11 patients with elevated transaminase levels had evidence of recent exposure, to Epstein-Barr virus as manifested either by Ox-cell hemolysin titers or rises in titers to viral capsid antigen.     

Typing of clinical herpes simplex virus isolates with mouse monoclonal antibodies to herpes simplex virus types 1 and 2: comparison with type-specific rabbit antisera and restriction endonuclease analysis of viral DNA

A total of 122 clinical isolates of herpes simplex virus (HSV) from 107 patients were typed by using an indirect immunoperoxidase technique with commercially available type-specific rabbit antisera, recently developed mouse monoclonal antibodies to HSV types 1 and 2, and restriction endonuclease analysis of viral DNA. With the commercially available type-specific rabbit antisera, 34% of clinical HSV isolates were of indeterminate type; 63% of them were typed as HSV type 1 and 37% as HSV type 2 by using monoclonal antibody and restriction enzyme typing systems. Typing by immunofluorescence assay with the monoclonal antibodies gave identical results to those obtained by restriction enzyme analysis. Simultaneous infection with both HSV types was demonstrated by monoclonal antibody typing in five isolates from three patients. These findings were subsequently confirmed by plaque purification and restriction endonuclease analysis of viral DNA. Monoclonal antibodies were as sensitive as restriction enzyme analysis for the typing of clinical HSV isolates. Because of their simplicity, they are more amenable to use in clinical laboratories than is restriction endonuclease analysis.     

A controlled trial comparing vidarabine with acyclovir in neonatal herpes simplex virus infection. Infectious Diseases Collaborative Antiviral Study Group

BACKGROUND. Despite the use of vidarabine, herpes simplex virus (HSV) infection in neonates continues to be a disease of high morbidity and mortality. We undertook a controlled trial comparing vidarabine with acyclovir for the treatment of neonatal HSV infection. METHODS. Babies less than one month of age with virologically confirmed HSV infection were randomly and blindly assigned to receive either intravenous vidarabine (30 mg per kilogram of body weight per day; n = 95) or acyclovir (30 mg per kilogram per day; n = 107) for 10 days. Actuarial rates of mortality and morbidity among the survivors after one year were compared overall and according to the extent of the disease at entry into the study (infection confined to the skin, eyes, or mouth; encephalitis; or disseminated disease). RESULTS. After adjustment for differences between groups in the extent of disease, there was no difference between vidarabine and acyclovir in either morbidity (P = 0.83) or mortality (P = 0.27). None of the 85 babies with disease confined to the skin, eyes, or mouth died. Of the 31 babies in this group who were treated with vidarabine and followed for a year, 88 percent (22 of 25) were judged to be developing normally after one year, as compared with 98 percent (45 of 46) of the 54 treated with acyclovir (95 percent confidence interval for the difference, -4 to 24). For the 71 babies with encephalitis, mortality was 14 percent with vidarabine (5 of 36) and with acyclovir (5 of 35); of the survivors, 43 percent (13 of 30) and 29 percent (8 of 28), respectively, were developing normally after one year (95 percent confidence interval for the difference, -11 to 39). For the 46 babies with disseminated disease, mortality was 50 percent (14 of 28) with vidarabine and 61 percent (11 of 18) with acyclovir (95 percent confidence interval for the difference, -20 to 40); of the survivors, 58 percent (7 of 12) and 60 percent (3 of 5), respectively, were judged to be developing normally after one year (95 percent confidence interval for the difference, -40 to 50). Both medications were without serious toxic effects. CONCLUSIONS. In this multicenter, randomized, blinded study there were no differences in outcome between vidarabine and acyclovir in the treatment of neonatal HSV infection. The study lacked statistical power to determine whether there were sizable differences within the subgroups of those with localized HSV, encephalitis, or disseminated disease.     

Evaluation of a quantitative competitive PCR assay for measuring herpes simplex virus DNA content in genital tract secretions.

Previous studies have shown an association between the approximate titer of herpes simplex virus (HSV) DNA in clinical specimens and the ability to isolate HSV from genital secretions. To control for variance in amplification conditions, we developed a competitive quantitative PCR (QC PCR) for the detection of HSV DNA. The assay accurately measured from 10 to 10(6) copies of HSV DNA. We compared the QC PCR with our previous semiquantitative detection method and found concordance for 61 of 63 positive specimens. We also evaluated the HSV DNA content from individual swabs of genital secretions obtained from individual sites of the genital tract (cervix, vulva, and rectum) with that from one swab with secretions from all three sites. The concordance for detecting HSV DNA was 91%; for only 4 of 143 collection days was there a > 1 log difference between the two collection methods. A single swab with secretions from all three genital sites and evaluated in a QC PCR format can accurately measure the frequency of subclinical and clinical shedding of HSV and the titer of HSV shed from the genital region. Such an approach should be very useful in the evaluation of antiviral chemotherapy for HSV.     

Clinical,hematologic, and immunologic effects of interleukin-10 in humans

We conducted a double-blind, placebo-controlled study to investigate the safety, pharmacokinetics, and immunological properties of interleukin-10 (IL-10) administration in healthy humans. Volunteers received a single intravenous bolus injection of recombinant human IL-10 (1, 10, or 25g/kg) or placebo. Cytokine production in whole blood and peripheral blood mononuclear cells (PBMC) was assessed before and 3, 6, 24, and 48 hr after the injection. Peak serum concentrations of IL-10 (15±1.1, 208±20.1, and 505±22.3 ng/ml) occurred after 2–5 min for 1, 10, and 25g/kg IL-10, respectively. The terminal-phase half-life was 3.18 hr. A transient leukocytosis (24–63% above baseline) was observed 6 hr after injection, which coincided with a dose-dependent decrease (12–24%) in neutrophil superoxide generation. There was a marked inhibition (60–95%) of endotoxin-induced IL-6 production from whole blood in each group receiving IL-10. Production of IL-8 in endotoxin-stimulated blood was reduced in the 10g/kg group. In PBMC stimulated with phytohemagglutinin and phorbol ester, there was a decrease (72–87%) in interferon- (IFN) production 6 hr after IL-10 with a return to pre-IL-10 levels after 24 hr. This reduction was only partially associated with a decrease in the number of CD2-bearing cells. We conclude that IL-10 administration into humans is without significant side effects, and a single injection reducesex vivo production of IL-6, IL-8, and IFN.     

Cloning of the nitrate reductase gene of Stagonospora (Septoria) nodorum and its use as a selectable marker for targeted transformation

The nitrate reductase gene (NIA1) of the phytopathogenic fungus Stagonospora (Septoria) nodorum has been cloned from a cosmid library by homologous hybridisation with a PCR-generated probe. A 6.7-kb fragment carrying the NIA1 gene was subcloned and partially characterised by restriction mapping. Sequencing of the gene indicated a high degree of homology, both at the nucleotide and amino-acid levels, with nitrate reductase genes of other filamentous fungi. Furthermore, consensus regulatory signals thought to be involved in the control of nitrogen metabolism are present in the 5′ flanking region. The cloned NIA1 gene has been used to develop a gene-transfer system based on nitrate assimilation. Stable nia1 mutants of S. nodorum defective in nitrate reductase were isolated by virtue of their resistance to chlorate. These were transformed back to nitrate utilisation with the wild-type S. nodorum NIA1 gene. Southern analyses revealed that transformation occurred as a result of the integration of transforming DNA into the fungal genome; in all cases examined, integration was targeted to the homologous sequence. Received: 30 March / 9 June 1998     

Contrasting Roles of Mannan-Specific Monoclonal Immunoglobulin M Antibodies in the Activation of Classical and Alternative Pathways by Candida albicans

Polyclonal antimannan immunoglobulin G (IgG) activates the classical complement pathway and accelerates initiation of the alternative pathway by Canidida albicans. This dual role was assessed for two antimannan IgM monoclonal antibodies (MAbs). MAb B6.1 is specific for an epitope on the acid-labile portion of C. albicans phosphomannan; MAb B6 is specific for an epitope on the acid-stable region. Both MAbs were potent activators of the classical pathway but poor facilitators of alternative pathway initiation.Candida albicans activates the human complement system via both the classical and the alternative pathways, leading to deposition of opsonic complement fragments on the yeast cell surface (8, 10, 18). In previous studies, we described a critical role for naturally occurring antimannan immunoglobulin G (IgG) in complement activation by C. albicans. Those studies used a kinetic assay for C3 deposition on the yeast and immunofluorescence evaluation of the sites of C3 binding (10, 17, 18). Deposition of C3 onto C. albicans cells incubated in normal human serum (NHS) occurs rapidly via the classical pathway and can be detected within the first 2 min of incubation. If the classical pathway is blocked by chelation of Ca²⁺ with EGTA, C3 deposition occurs via the alternative pathway, but C3 deposition is delayed and a 6-min incubation is required before bound C3 is readily detectable on the yeast surface. Removal of naturally occurring antimannan IgG from the serum by mannan absorption profoundly delays accumulation of C3 on the yeast cell surface, with 12 min or more of incubation being required before appreciable amounts of bound C3 are detected. However, this 12-min delay can be overcome by supplementation of the mannan-absorbed serum with affinity-purified human antimannan IgG in the absence of EGTA to mediate classical pathway initiation or shortened to 6 min in the presence of EGTA to allow antibody-facilitated activation of the alternative pathway. These observations demonstrate a dual role for antimannan IgG in serum from healthy adults in complement activation by C. albicans. Antimannan IgG mediates activation of the classical pathway and facilitates initiation of the alternative pathway (17, 18).In studies described above, we used polyclonal antimannan IgG purified from pooled human plasma. Since C. albicans cells express a number of immunodominant mannan components recognized by rabbits (15, 16), the human polyclonal antimannan IgG likely contains a range of specificities for distinct mannan determinants. It has been shown that rabbit antibodies that are reactive with three different cell wall determinants of group A streptococci display differential abilities to activate the classical or alternative pathway (2). Although the antibodies specific for three different cell wall epitopes all activated the classical pathway, only antibody specific for the N-acetyl-d-glucosamine epitope activated the alternative pathway (2). In a separate study, capsular as well as noncapsular antibodies were found to direct classical-pathway-mediated killing of Haemophilus influenzae type b, whereas only the capsular antibodies promoted killing by the alternative pathway (12). These studies provide evidence that epitope specificity may influence the ability of an antibody to activate the alternative pathway and prompted us to examine whether antibodies that recognize different mannan determinants are able to mediate activation of the classical and alternative pathways by C. albicans.Two IgM monoclonal antibodies (MAbs) that recognize distinct mannan determinants were compared for their abilities to activate the classical or alternative pathway. MAb B6.1 is specific for an acid-labile component of the Candida phosphomannan complex, and MAb B6 is specific for an acid-stable component (5). The MAbs were produced commercially (Montana ImmunoTech, Inc., Bozeman, Mont.).C. albicans CA-1 was grown as yeast forms to stationary phase in glucose (2%)-yeast extract (0.3%)-peptone (1%) broth for 24 h at 37°C as described elsewhere (4, 6, 10). The mannan of CA-1 yeast was purified as described previously (7, 18) and coupled to CNBr-Sepahrose 4B (Pharmacia Biotech, Uppsala, Sweden) (18).Pooled NHS was prepared from peripheral blood from at least 10 healthy adult donors and stored at −80°C. C3 was isolated from frozen human plasma (9, 13) and stored at −80°C until used. C3 was labeled with ¹²⁵I as described previously (3) by use of IODO-GEN reagent (Pierce, Rockford, Ill.). NHS was absorbed with mannan-Sepharose 4B to remove antimannan antibodies (18).Kinetics of C3 binding were assayed by the method of Kozel et al. (10). To determine whether MAb B6 or B6.1 activates the classical pathway, 2 × 10⁶ yeast cells were incubated at 37°C in 1 ml of a complement binding medium that contained (i) 40% NHS, mannan-absorbed serum, or mannan-absorbed serum supplemented with MAb B6 or B6.1, (ii) sodium Veronal (5 mM)-buffered saline (142 mM, pH 7.3) containing 0.1% gelatin, 1.5 mM CaCl₂, and 1 mM MgCl₂, and (iii) ¹²⁵I-labeled C3. To study whether MAb B6 or B6.1 plays a role in alternative pathway initiation, yeast cells were incubated in the manner described above except that the binding medium was not supplemented with Ca²⁺ and contained 5 mM EGTA and 5 mM MgCl₂. At various time intervals from 2 to 16 min, 50-μl samples were withdrawn in duplicate and added to 200 μl of phosphate-buffered saline–0.1% sodium dodecyl sulfate–20 mM EDTA in Millipore MABX-N12 filter plates fitted with BV 1.2-μm-pore-size filter membranes (Millipore, Bedford, Mass.). The cells were washed with phosphate-buffered saline–0.1% sodium dodecyl sulfate, and filter-bound radioactivity was determined with a gamma counter. Nonspecific binding was estimated from cells incubated in NHS containing EDTA and was subtracted from the total counts.Mannan absorption of serum profoundly delayed C3 accumulation on yeast from 2 min to approximately 10 min (Fig. ​(Fig.11 and ​and2).2). However, addition of either MAb B6 or MAb B6.1 at 50 μg per ml of reaction mixture to the absorbed serum generated rapid activation kinetics characteristic of C3 deposition via the classical pathway (Fig. ​(Fig.1)1) (10, 17, 18). This observation was not unexpected, as polyvalent IgM is known to be a potent activator of the classical pathway. Open in a separate windowFIG. 1Effect of MAb B6 or B6.1 on the kinetics of C3 deposition on C. albicans cells via the classical pathway. Yeast cells were incubated in a C3 binding medium containing (i) 40% NHS (•), (ii) 40% mannan-absorbed NHS (○), (iii) 40% mannan-absorbed NHS supplemented with MAb B6 (▴), or (iv) 40% mannan-absorbed NHS supplemented with MAb B6.1 (▿) at 50 μg per ml of reaction mixture. C3 deposition patterns from three independent assays were similar; results from one representative assay are shown.Open in a separate windowFIG. 2Effect of MAb B6 or B6.1 on the kinetics of C3 deposition on C. albicans cells via the alternative pathway. Yeast cells were incubated in a C3 binding medium containing (i) 40% NHS (•), (ii) 40% NHS–EGTA (■), (iii) 40% mannan-absorbed NHS containing EGTA (○), (vi) 40% mannan-absorbed NHS containing EGTA supplemented with MAb B6 (▴), or (iv) 40% mannan-absorbed NHS supplemented with MAb B6.1 (▿) at 50 μg per ml of reaction mixture. C3 deposition patterns from four independent assays were similar; results from one representative assay are shown.The effects of MAbs B6 and B6.1 on activation of the alternative pathway were assessed by addition of the antibodies to mannan-absorbed serum in the presence of EGTA. The results (Fig. ​(Fig.2)2) showed that neither MAb B6 nor MAb B6.1 at 50 μg per ml of reaction mixture altered the alternative pathway activity of the mannan-absorbed serum. To determine whether the inability of MAb B6 or B6.1 to facilitate initiation of the alternative pathway was influenced by antibody concentration, the experiment represented in Fig. ​Fig.22 was repeated with mannan-absorbed serum that was supplemented with 10 to 160 μg of MAb B6 or B6.1 per ml. These antibody concentrations were chosen because in our previous studies we found that affinity-purified human antimannan IgG activates both the classical and alternative pathways (17). However, at 10, 40, or 160 μg per ml of reaction mixture, both antibodies failed to enhance alternative pathway activity of mannan-absorbed serum but promoted classical pathway activity (data not shown).The observation that both MAbs were unable to enhance alternative pathway activity was unexpected. Our previous studies showed that addition of polyclonal antimannan IgG to mannan-absorbed NHS containing EGTA produced C3 binding kinetics that were indistinguishable from the kinetics observed with nonabsorbed NHS containing EGTA (17). We further demonstrated IgG-dependent initiation of the alternative pathway by C. albicans using the six purified alternative pathway proteins (17).There are at least three possible explanations for the failure of MAbs B6 and B6.1 to facilitate activation of the alternative pathway. First, it is possible that antimannan antibodies of the IgM class are unable to enhance C3 deposition via the alternative pathway. However, there is evidence that polyclonal IgM is able to enhance alternative pathway-mediated lysis of rabbit erythrocytes by NHS (11, 14). Second, the ability of an antibody to facilitate deposition of C3 via the alternative pathway could be epitope specific; MAbs B6 and B6.1 could have the wrong epitope specificity. As noted above, Eisenberg and Schwab (2) found that polyclonal antibodies specific for one antigen found on group A streptococcal cell walls were able to facilitate initiation of the alternative pathway, whereas antibodies specific for two other antigens were not. If antibody-facilitated activation of the alternative pathway is dependent on epitope specificity, such a finding might influence strategies for induction of protective immunity to Candida. Optimal immunization may require an immunogen that induces antibodies with epitope specificities needed to facilitate activation of the alternative pathway. Finally, we cannot exclude the possibility that human antimannan antibodies are able to facilitate activation of the alternative pathway, whereas mouse antibodies lack this capability.In studies involving a murine model of disseminated candidiasis, MAb B6.1 was shown to be protective, whereas MAb B6 was not (4). However, the protection mechanisms remain to be elucidated. In an in vitro assay, MAb B6.1 but not MAb B6 was found to enhance candidacidal activity of polymorphonuclear leukocytes in the presence of fresh mouse serum, suggesting the involvement of mouse complement in the killing (1). Although assessing the role of complement in MAb B6.1-mediated protection was beyond the scope of this study, our observation that the two antibodies mediate similar kinetics of C3 deposition for C. albicans does not preclude the possibility that the composition and/or accessibility of opsonic complement fragments bound to the yeast cells might differ following complement activation by these two antibodies. Alternatively, the concerted action of several protective functions, including activation of the complement system, may be required for MAb B6.1-mediated protection.     

Nonrandom chromosomal changes in untreated retinoblastomas

The karotypic patterns of 15 retinoblastomas were examined. Five tumors were found to have two distinct stem lines and, therefore, the chromosomal patterns of 20 tumor cell lines are reported. Three nonrandom chromosomal changes, namely, a loss of a chromosome #13, the presence of an i(6p), or a trisomy of 1q were observed. The potential importance of these chromosomal changes in tumor development is discussed, particularly the loss of a chromosome #13 or the gain of an i(6p). At least one of the three chromosomal changes was found in 75% of the tumor lines analyzed.