Collaborative study to assess the suitability of a proposed working reagent for human parvovirus B19 DNA detection in plasma pools by gene amplification techniques. B19 Collaborative Study Group

BACKGROUND AND OBJECTIVES

A collaborative study was done to examine the sensitivity and specificity of assays for the detection of human parvovirus B19 DNA in plasma pools by PCR techniques and to establish a working reagent for B19 DNA testing of plasma pools.

MATERIALS AND METHODS

Duplicate samples consisting of a tenfold dilution series of a positive cryosupernatant diluted in B19 DNA-negative cryosupernatant were sent to 17 laboratories.

RESULTS

The sensitivity of the assays varied: 2 laboratories were able to detect the 10(-7) dilution while 1 laboratory failed to detect B19 DNA in any samples. In addition, 5 laboratories obtained false-positive results.

CONCLUSIONS

In general, laboratories using assays optimised for rapid detection of B19 DNA in serum samples did not perform well, indicating that such rapid methods are not adequate for examination of plasma pools. The 10(-6) dilution was detected by approximately half the laboratories and could be used as the working reagent.

Humanization of a mouse antibody against human alpha-4 integrin: a potential therapeutic for the treatment of multiple sclerosis

alpha 4 beta 1 integrin (VLA-4) is crucial for the adhesion of leukocytes to human vascular cell adhesion molecule-1 (VCAM-1) on inflamed endothelium. This cell adhesion event is the first step in leukocyte extravasation across the blood-brain barrier in inflammatory diseases of the central nervous system (CNS) such as experimental autoimmune encephalomyelitis (EAE). Prevention of leukocyte infiltration by antibodies against the alpha 4 integrin, which block the alpha 4 beta 1 integrin/VCAM-1 interaction, have been shown to suppress clinical and pathological features of EAE. In this study, two mouse monoclonal antibodies (MAb) directed against human alpha 4 integrin were analyzed in vitro for their ability to block the interaction of leukocytes with VCAM-1 under different assay conditions. The best blocking MAb, AN100226m, was humanized by complementarily-determining region grafting, associated with human C regions and expressed. We found that modification of two structural determinants (H27 and H29) for the heavy chain CDR1 loop in one hand, and modification of framework amino acid H38, H40 and H44 in the other hand, had no effect on antigen binding. In contrast, modification of a structural determinant (H71) for the heavy chain CDR2 loop resulted in loss of binding. The humanized antibody. AN100226, was equivalent to the murine antibody. AN100226m, in binding to alpha 4 beta 1 integrin and in blocking cell adhesion. More importantly, AN100226 was as effective as AN100226m in the reversal of active EAE in guinea pigs and thus may be useful in the treatment of autoimmune diseases such as multiple sclerosis. AN100226 is currently in phase II clinical trials in the UK for the treatment of multiple sclerosis exacerbations.

Report of EPFA/NIBSC workshop 'nucleic acid amplification tests (NAT) for the detection of blood-borne viruses' held on 31 October 1996 in Amsterdam, The Netherlands

The 3rd annual European Plasma Fractionators Association/National Institut of Biological Standard and Control (EPFA/NIBSC) meeting provided a forum for regulators, blood product and test kit manufacturers and organisations developing standards to present and discuss their latest data. The main conclusions were as follows. There has been substantial progress during the last year in the development of NAT technology specifically for improving the safety of blood products though there is an urgent need for the development of international reference materials. The technology is not yet sufficiently developed to be used as a routine screening test though testing of plasma pools for hepatitis C virus may be achieved within a year. Introduction of testing should not result in the creation of dual standards for plasma derived and cellular products. Once the technology is fully developed it could significantly improve the safety of all blood products, particularly those derived from starting materials with a high incidence of viral markers.

Detection of human parvovirus B19 DNA in plasma pools and blood products derived from these pools: implications for efficiency and consistency of removal of B19 DNA during manufacture

The polymerase chain reaction (PCR) assay was used to detect human parvovirus B19 DNA in 38 blood products and start plasma pools from five different manufacturers. The products examined were albumin, factor VIII, intravenous (i.v.) and intramuscular (i.m) immunoglobulin batches. The majority of pools from all the manufacturers had detectable B19 DNA (64/75:85%; ranging from 60% to 100% for individual manufacturers). B19 DNA was found in 3/12 albumin samples, in 7/7 factor VIII samples, 3/15 IVIG samples and 3/4 IMIG samples. The levels of B19 DNA in pools varied from 10(2) to 10(9) genome equivalents/ml, whereas the levels in products varied from 10(2) to 10(6) genome equivalents/ml, but there was no clear relationship between the levels of B19 DNA in start pools and final products. The levels of B19 DNA varied between different batches of the same product from a single manufacturer, possibly due to small variations in the processing parameters. In addition, there was some indication from the study of IVIG samples that treatment at low pH may result in removal of PCR-detectable B19 DNA.

Collaborative study to assess the suitability of an HCV RNA reference sample for detection of an HCV RNA in plasma pools by PCR

A collaborative study was undertaken to examine the sensitivity and reproducibility of hepatitis C virus (HCV) RNA PCR assays of plasma pools in order to establish a reference sample for HCV PCR testing of plasma pools. Samples consisting of an HCV-RNA-positive donation diluted tenfold in an HCV-RNA-negative cryosupernatant were sent to 16 participating laboratories (including blood product manufacturers and control authorities). The results of the in-house assays indicate that a 10(-4) dilution of the positive donation in the cryosupernatant could be used as the reference sample as this was the highest dilution of the positive donation that was detected in all assays. In contrast, the results obtained with a commercially available assay, designed for use with single-donation plasma or serum (Roche Amplicor TM HCV test), were not so clear-cut and the assay appeared to be ten-fold less sensitive than the in-house assays.

Structural studies on the PH domains of Db1, Sos1, IRS-1, and beta ARK1 and their differential binding to G beta gamma subunits

Pleckstrin homology (PH) domains are approximately 110 amino acid residues in length and are structurally conserved in a number of intracellular signaling proteins. A role for these domains has been postulated for beta ARK, which binds to G beta gamma subunits. We have quantified the binding of individual (His)6-tag PH domains of human Db1, human Sos1, rat IRS-1, human beta ARK, and human beta ARK with an extra 33-residue C-terminal extension (beta ARK + C) to G beta gamma subunits. Our in vitro binding studies show that all of the PH domains (apart from Sos1), bind G beta gamma subunits in a dose-dependent manner, but beta ARK + C binds 4 times as much G beta gamma at saturation as the others. The IRS-1 PH domain has a similar half-maximal concentration of G beta gamma binding (18 nM) to beta ARK + C (30 nM), suggesting that the IRS-1 PH domain has sufficient determinants for G beta gamma binding. The beta ARK PH domain alone has a half-maximal value of 45 nM but a drastically reduced extent of G beta gamma binding, suggesting that both the PH domain and the C-terminal 33 residues are necessary for maximal binding. Db1 has a half-maximum concentration of G beta gamma binding of 45 nM and a maximal extent of binding similar to that of beta ARK, but it is difficult to demonstrate saturable binding of G beta gamma to Sos1. Since it was previously predicted that the C-terminal PH domain of Pleckstrin [Tyers, M., et al. (1988) Nature 333, 470-473] contains a potential calcium binding site, we have tested the different PH domains for calcium binding. Only the PH domain of Db1 bound 45Ca2+ with a Kd of 10 microM. CD spectroscopy of the purified recombinant PH domains indicated that they are predominantly beta-sheet structures.(ABSTRACT TRUNCATED AT 250 WORDS)

Sequence and structure of VH domain from naturally occurring camel heavy chain immunoglobulins lacking light chains

We cloned 17 different PCR fragments encoding VH genes of camel (Camelus dromedarius). These clones were derived from the camel heavy chain immunoglobulins lacking the light chain counterpart of normal immunoglobulins. Insight into the camel VH sequences and structure may help the development of single domain antibodies. The most remarkable difference in the camel VH, consistent with the absence of the VL interaction, is the substitution of the conserved Leu45 by an Arg or Cys. Another noteworthy substitution is the Leu11 to Ser. This amino acid normally interacts with the CH1 domain, a domain missing in the camel heavy chain immunoglobulins. The nature of these substitutions agrees with the increased solubility behavior of an isolated camel VH domain. The VH domains of the camels are also characterized by a long CDR3, possibly compensating for the absence of the VL contacts with the antigen. The CDR3 lacks the salt bridge between Arg94 and Asp101. However, the frequent occurrence of additional Cys residues in both the CDR1 and CDR3 might lead to the formation of a second internal disulfide bridge, thereby stabilizing the CDR structure as in the DAW antibody. Within CDRs of the camel VH domains we observe a broad size distribution and a different amino acid pattern compared with the mouse or human VH. Therefore the camel hypervariable regions might adopt structures which differ substantially from the known canonical structures, thereby increasing the repertoire of the camel antigen binding sites within a VH.

A sensitive PCR method for detecting HCV RNA in plasma pools, blood products, and single donations

Although current manufacturing processes appear to efficiently inactivate hepatitis C virus (HCV), it is possible that contaminated blood products may result from failure of some stage during manufacture or from virus overload of plasma pools used for preparation of products. While antibody screening probably removes the majority of HCV positive donations, some donations which are antibody-negative but HCV positive may be included in pools. The HCV RNA content of plasma pools from paid and voluntary donors was investigated by polymerase chain reaction (PCR). A sensitive PCR method using a single pair of primers from the 5' non-coding region of the HCV genome and a "hot-start" was established and shown to be as sensitive as the more conventional nested PCR (which uses two pairs of primers). The majority of pools from paid donors (prescreening) were HCV RNA positive, while all pools from voluntary donors were both antibody and RNA negative. Intravenous immunoglobulins prepared from contaminated pools were RNA negative despite having high antibody levels, indicating satisfactory clearance of the virus during manufacture. The virus load of the pools was at least a thousand-fold lower than that of single donations, possibly as a result of treatment during the production of the pools or the presence of factors in pools which reduce the sensitivity of some part of the PCR assay. The HCV content of a plasma donation was determined as 3.6 x 10(6) genomes/ml by an end point dilution method. Thus a simple and sensitive PCR assay was established for detecting HCV RNA in plasma pools and blood products.

Humanization of a mouse anti-human interleukin-6 receptor antibody comparing two methods for selecting human framework regions

Mouse monoclonal antibody AUK12-20 binds to human IL-6 receptor and inhibits IL-6 functions. It has been humanized by CDR-grafting for therapeutic use. In the design of reshaped human AUK12-20 VL region, the human framework regions (FRs) from the human Bence-Jones protein REI were used. The reshaped human AUK12-20 light chain, in combination with chimeric AUK12-20 heavy chain, bound to antigen as well as chimeric AUK12-20 antibody. In the design of reshaped human AUK12-20 VH region, two sets of the human FRs were chosen and compared. One set was from the consensus amino acid sequence for human VH regions subgroup (HSG)-I and the other set was from human antibody HAX, the most similar human VH region found in a database of human immunoglobulin sequences. The HSG-I-based and the HAX-based reshaped human AUK12-20 heavy chains in combination with the reshaped human AUK12-20 light chain, showed approximately 90 and 100% antigen-binding and competition-binding activities as compared to the chimeric or mouse AUK12-20 heavy chains. Most importantly, these humanized antibodies inhibited the IL-6-dependent tumor cell growth as well as the original mouse antibody suggesting that these humanized antibodies could be efficacious in human patients. Our results show that both approaches for the design of reshaped human antibodies can be used for successful humanization. The approach based on FRs from the most similar individual human antibody, however, seemed to be best for designing a reshaped human antibody that mimicked as closely as possible the original mouse antibody.

Humanization of a mouse anti-human IgE antibody: a potential therapeutic for IgE-mediated allergies

Mouse mAb TES-C21(C21) recognizes an epitope on human IgE and, therefore, has potential as a therapeutic agent in patients with IgE-mediated allergies such as hay fever, food and drug allergies and extrinsic asthma. The clinical usefulness of mouse antibodies is limited, however, due to their immunogenicity in humans. Mouse C21 antibody was humanized by complementarity determining region (CDR) grafting with the aim of developing an effective and safe therapeutic for the treatment of IgE-mediated allergies. The CDR-grafted, or reshaped human, C21 variable regions were carefully designed using a specially constructed molecular model of the mouse C21 variable regions. A key step in the design of reshaped human variable regions is the selection of the human framework regions (FRs) to serve as the backbones of the reshaped human variable regions. Two approaches to the selection of human FRs were tested: (i) selection from human consensus sequences and (ii) selection from individual human antibodies. The reshaped human and mouse C21 antibodies were tested and compared using a biosensor to measure the kinetics of binding to human IgE. Surprisingly, a few of the reshaped human C21 antibodies exhibited patterns of binding and affinities that were essentially identical to those of mouse C21 antibody.

Partial control of hepatitis delta virus superinfection by immunisation of woodchucks (Marmota monax) with hepatitis delta antigen expressed by a recombinant vaccinia or baculovirus

We have successfully limited the level of hepatitis delta viraemia occurring after superinfection of hepadna-virus infected woodchucks by prior immunisation with the short form of the hepatitis delta virus antigen expressed by a recombinant baculovirus or vaccinia virus. This phenomenon occurred in the absence of detectable circulating antibody to hepatitis delta virus antigen and in the absence of evidence of priming of the humoral immune response and may reflect the induction of a cytotoxic T-cell response. The latter would control viraemia by rapid lysis of delta antigen expressing hepatocytes. It is suggested that the T-cell epitopes involved may be located on the carboxyl end of the delta protein (amino acids 77-195).

Reshaping a human antibody to inhibit the interleukin 6-dependent tumor cell growth

The mouse PM-1 monoclonal antibody binds to the human interleukin 6 receptor, inhibits IL-6 functions, and shows strong antitumor cell activity against multiple myeloma cells. In order to be effective as a therapeutic agent administered to human patients in repeated doses, reshaped human PM-1 antibodies consisting of human REI-based light chain and NEW-based heavy chain variable regions were designed and constructed with the assistance of a structural model of the mouse PM-1 variable regions. The best reshaped human PM-1 antibody is equivalent to mouse or chimeric PM-1 antibody in terms of antigen binding and growth inhibition against multiple myeloma cells. Only a few minor changes in the human framework regions were required to recreate the mouse PM-1 antigen-binding site within a human antibody. The reshaped human PM-1 antibody, therefore, could be efficacious in human multiple myeloma patients.

Assays for viral sequences and their value in validation of viral elimination

Plasma pools and blood products were analysed for hepatitis C virus (HCV) RNA by the polymerase chain reaction (PCR). Initially, samples were amplified by "nested" PCR using two pairs of primers from the highly-conserved 5' non-coding region of the genome. The method was later modified to amplification with only the outer pair of primers and a "hot-start" to eliminate amplification of non-target sequences. The modified method was as sensitive as "nested" PCR. However, with samples containing low levels of RNA, it is necessary to perform repeat amplifications to avoid false-negative results. Ten out of 17 anti-HCV positive pools from paid donors were positive, while none of the 12% pools from unpaid donors was positive for RNA or anti-HCV antibodies. Four i.v. immunoglobulins made from contaminated pools were virus-free, indicating removal of virus during current manufacturing processes. A quantitative PCR method was established using a positive donation. Probit analysis gave an estimated viral titre of 3.6 x 10(6) genomes/ml.

Optimization of primers for cloning libraries of mouse immunoglobulin genes using the polymerase chain reaction

We have optimized primers for cloning libraries of murine heavy and light chain variable regions using the polymerase chain reaction. Since we are interested in cloning murine Fab fragments for expression in bacterial cells, the heavy chain primers were designed to clone Fd fragments comprising the heavy chain variable domain and the first domain of the IgG constant region. The light chain primers were designed to clone the entire murine kappa chain. Using ten degenerate 5' primers and a degenerate 3' primer to amplify murine Fd and seven degenerate 5' primers with a single 3' primer to amplify kappa chains, a diverse repertoire of mouse variable regions was cloned from mouse spleens.

Co-expression of markers for hepatitis delta and hepatitis B viruses in human liver

Delta hepatitis (HDV) infection can only occur in the presence of hepatitis B (HBV) infection, as HDV requires a coat of HBV surface antigen (HBsAg) for assembly of complete virus. A number of studies have examined the variation of HBV markers in serum and liver during establishment of HDV infection, but none has systematically examined the relationship between the two viruses in individual hepatocytes. Liver biopsies from five patients with HDV/HBV infection were stained for HBsAg, HBV core antigen (HBcAg) and hepatitis D (delta) antigen (HDAg). Double immunostaining was performed with a combination of indirect immunoperoxidase and alkaline phosphatase/antialkaline phosphatase techniques. HDV and HBV antigens were expressed in all five liver biopsies. Co-localization of HBsAg was seen in up to 39% of HDAg positive cells, and HBcAg in up to 8% of HDAg positive cells. HBcAg was detectable in approximately 9% of HBsAg positive cells, and HBsAg in approximately 12% of HBcAg positive cells. HDV can replicate without HBV but ultimately requires HBV to produce complete virus and subsequently infect other cells. In this study the majority of HDV positive cells did not appear to contain HBV markers. This might suggest delta virus replication without assembly, or possibly sequential production/assembly of the virus.

Integration of hepatitis B virus DNA through a mutational hot spot within the cohesive region in a case of hepatocellular carcinoma

Integrated hepatitis B virus (HBV) DNA previously cloned from a hepatocellular carcinoma genomic library derived from a Japanese patient was characterized further. Sequence analysis of restriction fragments bearing the virus-host junctions defined 3125 nucleotides of essentially un-rearranged HBV DNA of the adr subtype with the right junction mapping within the cohesive region at position 1970 and the left within the pre-core at position 1886. The right viral-host junction contains a 7 bp repeat (TGTAGGC) and a possible 2 bp inversion. The integrated HBV DNA includes the complete open reading frames for core, pre-S, S and polymerase and a 3' truncated X gene, and lacks most of the pre-core. Integration has occurred at a mutational hot spot of the viral genome and appears to be located in a region of semi-repetitive genomic DNA 3' to the beta-globin gene cluster.

Humanization of a mouse monoclonal antibody by CDR-grafting: the importance of framework residues on loop conformation

A mouse monoclonal antibody (mAb 425) with therapeutic potential was 'humanized' in two ways. Firstly the mouse variable regions from mAb 425 were spliced onto human constant regions to create a chimeric 425 antibody. Secondly, the mouse complementarity-determining regions (CDRs) from mAb 425 were grafted into human variable regions, which were then joined to human constant regions, to create a reshaped human 425 antibody. Using a molecular model of the mouse mAb 425 variable regions, framework residues (FRs) that might be critical for antigen-binding were identified. To test the importance of these residues, nine versions of the reshaped human 425 heavy chain variable (VH) regions and two versions of the reshaped human 425 light chain variable (VL) regions were designed and constructed. The recombinant DNAs coding for the chimeric and reshaped human light and heavy chains were co-expressed transiently in COS cells. In antigen-binding assays and competition-binding assays, the reshaped human antibodies were compared with mouse 425 antibody and to chimeric 425 antibody. The different versions of 425-reshaped human antibody showed a wide range of avidities for antigen, indicating that substitutions at certain positions in the human FRs significantly influenced binding to antigen. Why certain individual FR residues influence antigen-binding is discussed. One version of reshaped human 425 antibody bound to antigen with an avidity approaching that of the mouse 425 antibody.

The application of SSADM to modelling the logical structure of proteins

A logical design that describes the overall structure of proteins, together with a more detailed design describing secondary and some supersecondary structures, has been constructed using the computer-aided software engineering (CASE) tool, Auto-mate. Auto-mate embodies the philosophy of the Structured Systems Analysis and Design Method (SSADM) which enables the logical design of computer systems. Our design will facilitate the building of large information systems, such as databases and knowledgebases in the field of protein structure, by the derivation of system requirements from our logical model prior to producing the final physical system. In addition, the study has highlighted the ease of employing SSADM as a formalism in which to conduct the transferral of concepts from an expert into a design for a knowledge-based system that can be implemented on a computer (the knowledge-engineering exercise). It has been demonstrated how SSADM techniques may be extended for the purpose of modelling the constituent Prolog rules. This facilitates the integration of the logical system design model with the derived knowledge-based system.

Molecular model-building of amylin and alpha-calcitonin gene-related polypeptide hormones using a combination of knowledge sources

Amylin is the major component of the amyloid found in the pancreases of noninsulin-dependent diabetics (type 2 diabetes). It is a 37 amino acid polypeptide and has been shown to have 46% sequence identity with the neuropeptide alpha-calcitonin gene-related peptide (alpha-CGRP). Both amylin and alpha-CGRP are known to be potent inhibitors of glycogen synthesis in stripped rat soleus muscle. Secondary structure prediction and tertiary structure model-building show the two polypeptides to have an alpha-helix/beta-strand motif similar to that observed in the insulin B-chain. The results have been supported by CD spectroscopy, although there is no sequence similarity between insulin and amylin/alpha-CGRP. Aggregation states have been predicted based on the dimeric and hexameric arrangements seen in porcine insulin. Rat and hamster amylin have a changed sequence motif in the beta-strand which results in lack of amyloid formation and type 2 diabetes. This, we propose, is caused by disruption of hydrogen bonding which prevents the formation of the dimer.

A novel method for the modelling of peptide ligands to their receptors

A knowledge-based approach to the modelling of enzyme-peptide inhibitor complexes is described. Given the structure of an enzyme, and knowledge of its binding site, the method seeks to predict the binding geometry of a peptide ligand. This novel method involves using examples of side-chain packing derived from proteins of known three-dimensional structure to define possible packing arrangements of a peptide inhibitor group to its binding site. A suite of programs, GEMINI, was written and used to predict the packing of pairs of amino acid groups from three inhibitors complexed to their enzymes for which the X-ray structures were available. These included the Phe group of the inhibitor H142 bound to endothiapepsin, the Leu group of CLT complexed to thermolysin and the C-terminus of Gly-L-Tyr bound to carboxypeptidase A. A detailed comparison of the modelled and observed inhibitor coordinates was made. This approach may be extended to modelling other types of protein interactions.

Immunization of woodchucks with recombinant hepatitis delta antigen does not protect against hepatitis delta virus infection

To assess the role of immunization against hepatitis delta antigen in the prevention of hepatitis delta virus infection, woodchuck carriers of woodchuck hepatitis virus were immunized with a 64 amino acid portion of hepatitis delta antigen from its N-terminal region. The protein was expressed in Escherichia coli and contained a major immunogenic epitope. A significant anti-hepatitis delta response was observed that did not, however, protect the animals from hepatitis delta virus superinfection. Unexpectedly, the period of detectable viremia was longer in the immunized than in the control animals. We conclude that immunization with this recombinant hepatitis delta antigen does not afford protection against subsequent hepatitis delta virus exposure.

The epidermolytic toxins are serine proteases

Certain strains of Staphylococcus aureus usually belonging to phage group II produce epidermolytic toxins (ETA and ETB) which cause intraepidermal splitting in mice, neonates and occasionally adults. Amino acid sequences of ETA and ETB have been reported but the mechanism of epidermolysis remains unknown. A search of the NBRF-PIR computer database showed the toxins to have significant sequence similarity with staphylococcal V8 protease and that the catalytic triad of V8 protease is present in ETA and ETB. Comparison of ETA, ETB and V8 protease with other members of the trypsin-like serine protease family revealed little homology save for the immediate vicinity of the residues constituting the catalytic triad. The toxins, therefore, exhibit a distant relationship to mammalian serine proteases. A potential Ca2(+)-binding loop was identified in ETA (but not ETB) on the basis of sequence similarity with the second calcium-binding loop of rat intestinal calcium-binding protein. Epidermolysis produced by ETA in the mouse bioassay was shown to be inhibited by the presence of EDTA consistent with a Ca2(+)-dependent mechanism.

Cloning and expression of an immunodominant region of the hepatitis delta antigen

A cDNA clone prepared from hepatitis delta virus (HDV) RNA extracted from human serum was subcloned in the bacterial expression vector pPL31 to produce a fusion protein consisting of the first 98 amino acids of MS2 polymerase and of 64 amino acids from near the N-terminal region of hepatitis delta antigen (HDAg). The fusion protein was shown to be related to HDAg by a commercial sandwich immunoassay (Abbott) and immunoblotting with human anti-HDAg serum. Antiserum against the fusion protein was raised in rabbits and used to identify HDAg extracted from the serum and liver of an HDV-infected woodchuck and chimpanzee and from the serum of an HDV-infected human, by immunoblotting and immunohistology. A single, major polypeptide of 24K was detected in both serum and liver extracts, with a minor polypeptide of 26K sometimes present. Liver extracts also contained lower Mr polypeptides thought to be degradation products, the major species being 22.5K. The same pattern of staining was obtained with human anti-HDAg serum. Absorption experiments with the expressed protein and cross-competition experiments with the rabbit antiserum suggest that a major immunodominant region of HDAg is present near the N-terminal end of the antigen, between positions 1561 and 1368 on the genome. Both the expressed protein and rabbit antiserum were shown to be good diagnostic reagents.

Detection of hepatitis delta virus RNA in chronic liver disease

A series of 120 patients with chronic delta hepatitis virus (HDV) were investigated using a newly developed assay for the detection of serum delta RNA and this marker was correlated with other markers of HDV infection. The assay was shown to be both specific and sensitive and provides a direct non-invasive measurement of HDV infectivity. Serum HDV RNA was detected in 51.2% of all patients and in about 64% of those who were liver HDV antigen positive. Its presence was particularly associated with the early stages of the disease where it was found in 83% of cases with chronic active hepatitis (CAH) and progressively less common in CAH associated with cirrhosis and in inactive cirrhosis. The presence of both HBeAg (and HBV DNA) and high levels of HDV RNA in the sera of 5 of the patients analysed, clearly demonstrates simultaneous replication of both HBV and HDV. The serum HDV RNA 'slot blot' assay described in this study should prove invaluable in elucidating further the natural history of delta hepatitis and in monitoring antiviral therapy.

Detection of HSV1 DNA by in situ hybridisation in human brain after immunosuppression

Human brain cells were examined for the presence of herpes simplex virus type 1 (HSV1) DNA sequences by in situ hybridisation. Viral genome was detected in immunosuppressed patients with virological evidence of past HSV infection but not in immunosuppressed patients with no such evidence. In patients who had not been immunosuppressed, no HSV DNA sequences were detectable.

Virus infections in immunocompromised patients: their importance and their management

Opportunistic viral infections were investigated in 156 adult patients admitted over one year to a medical oncology service: 35% of the total group and 65% of those with acute leukaemia experienced viral infections, 79% of which were with viruses of the herpes group. Surprisingly few enteric viruses were recovered. Reactivation of herpes simplex virus in the brains of these immunosuppressed patients was suggested by the demonstration by nucleic acid hybridization of herpes simplex virus DNA sequences in neurones and endothelial cells in patients with evidence of past infection with virus. Acyclovir was effective in therapy and prophylaxis. Twenty-three strains from 7 patients were tested for sensitivity to this antiviral: in 3 instances clinical resistance was observed but the strains were fully sensitive in vitro, as were all other strains tested.

An improved method for preparing DNA from human brain

The preparation of DNA from human brain by conventional protease and RNAase digestion, phenol-chloroform extraction and ethanol precipitation results in very low yields. This is probably due to interference by lipid present at very high levels in this tissue. We have overcome this by solubilizing the initial tissue homogenate by heating at 60 degrees C for 30 min in sodium dodecyl sulphate. This results in a threefold increase in yield and a considerable reduction in preparation time. The molecular weight of the DNA is greater than 20 X 10(6) milion.

The projection of the lateral geniculate nucleus to area 17 of the rat cerebral cortex. II. Terminations upon neuronal perikarya and dendritic shafts

The forms of dendrites in layer IV receiving degenerating thalamocortical axon terminals directly on their shafts were examined in serial thin sections. Reconstructions showed these dendrites varied in thickness between 2.5 and 0.5 mum. They had essentially smooth contours and rarely showed evidence of protrusions or spines. They were further characterized by the presence of many synapses along their shafts. Only about one in 12 of these synapses was formed by degenerating thalamocortical axon terminals. These smooth dendrites emerged from neuronal perikarya that also received degenerating axon terminals which formed asymmetric synaptic junctions. Such cell bodies bore both symmetric and asymmetric synaptic junctions, and not all of the latter were caused to degenerated after a thalamic lesion. These postsynaptic neurons appeared to be of two kinds, ones with thin dendrites that often contained closely packed microtubules, and others with thicker dendrites that emerged from the poles of oval perikarya.