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Biomedical subjects

A B Heath

Publications and source records attributed to A B Heath.

At least 37 records · Page 2Linked to original sources
PubMed1994

A collaborative study of the histopathological evaluation of the WHO neurovirulence test for poliovirus vaccines.

A collaborative study evaluated the histopathological examination of the WHO neurovirulence test for poliovirus vaccines. Participants scored two sets of slides and the slides were sent to all participants in turn. The results showed an approximately two-fold range in mean lesion scores between readers. As readers scored consistently high or low, however, the range of differences between the two sets of slides was considerably less. From the limited data available, these differences in scoring would not have resulted in different decisions on the acceptability of the particular vaccines included in this study. The study was of value in assisting in developing mutual confidence in the interpretation of histological lesions in the neurovirulence test.

Animals↗
PubMed1993

A European collaborative study to assess the proficiency of laboratory estimates of potency of live measles, mumps and rubella tri-valent vaccines.

A collaborative study involving 10 European laboratories was undertaken to assess the variability of estimates of the potency of measles, mumps and rubella tri-valent vaccines. The precision of assays as demonstrated by tests on duplicate samples was good; differences averaged around 0.2 log10 steps. Similarly, assay to assay variation within laboratories was small with most achieving consistency around 5% over three assays. In contrast, overall median variations in potency between laboratories were around 1.0 log10 for measles, 3.0 log10 for mumps and 2.0 log10 for rubella. Unexpectedly, the variations in estimates for measles and rubella were not improved when potencies were expressed relative to reference preparations. However, for mumps variability was reduced by using a reference but only for the vaccines of the same strain as the reference. For these Urabe mumps vaccines the variation in relative potency was around 1.5 log10.

Drug Combinations↗
PubMed1993

Sequence variation in the env gene of simian immunodeficiency virus recovered from immunized macaques is predominantly in the V1 region.

Three cynomolgus macaques were immunized with recombinant envelope protein preparations derived from simian immunodeficiency virus (SIV). Although humoral and cellular responses were elicited by the immunization regime, all macaques became infected upon challenge with 10 MID50 of the 11/88 virus challenge stock of SIVmac251-32H. The polymerase chain reaction was used to amplify proviral SIV gp120 sequences present in the blood of both immunized and control macaques at 2 months post-infection. A comparison of the predominant sequences found in the region from V2 to V5 of gp120 failed to differentiate provirus recovered from either immunized or control animals. A detailed investigation of sequences obtained from the hypervariable V1 region identified a mixture of sequences in both immunized and control macaques. Some sequences were identical to those previously detected in the virus challenge stock, whereas others had not been detected previously. Phenogram analysis of the new V1 sequences found in immunized animals revealed that they were quite distinct from those from the virus challenge stock and that they included alterations to potential N-linked glycosylation sites. In contrast, new sequence variants recovered from the control animals were closely related to sequences from the virus challenge stock. The difference in diversity of new V1 sequences recovered from immunized and control macaques was highly significant (P < 0.001). Thus, the presence of pre-existing immune responses to SIV envelope protein is associated with greater genetic change in the V1 region of gp120. These data are discussed in relation to the epitopes of SIV gp120 that may confer protection from in vivo challenge.

Amino Acid Sequence↗
PubMed1993

Working standards for hepatitis B surface antigen for use in the UK Blood Transfusion Service: results of a collaborative study.

Twenty-six laboratories including 22 Blood Transfusion Centres in England, Scotland, Wales and Northern Ireland participated in a collaborative study to assess the suitability of proposed working standards for hepatitis B surface antigens (HBsAg) for use in the UK Blood Transfusion Service. Data from 88 assays indicated that all laboratories could detect HBsAg in the proposed working standard at a concentration of 0.5 IU/ml. Samples containing HBsAg at a concentration of 0.125 IU/ml were scored positive in 80% of assays and it was concluded that this would be a suitable concentration for inclusion in a monitor sample which would indicate whether the sensitivity of an assay system in routine use is varying over a period of time. The use of a batch of 'provisional' working standard tested under field conditions over a period of 4 months has been monitored. HBsAg was not detected in only 2 out of 6,523 assays.

Blood Banks↗
PubMed1992

Standardisation of factor VIII--V. Calibration of the 2nd International Standard for Factor VIII and von Willebrand factor activities in plasma.

The proposed 2nd International Standard for Factor VIII and von Willebrand Factor activities in plasma, NIBSC code 87/718, was assayed against the 1st IRP, 80/511, and against fresh normal plasma, in 21 laboratories. There were no significant differences between the various assay methods for factor VIII antigen, von Willebrand factor antigen, and von Willebrand factor ristocetin co-factor activity. For factor VIII clotting activity there was a significant difference between the results of one-stage and two-stage assays. Plasma 87/718 has now been established by the WHO Expert Committee on Biological Standardisation as the 2nd IS for factor VIII and vWF in plasma with the following potencies: VIII:C 0.60 IU/ampoule; VIII:Ag 0.91 IU/ampoule; vWF:Ag 0.91 IU/ampoule; vWF/RCo 0.84 IU/ampoule.

Blood Chemical Analysis↗
PubMed1992

A collaborative study to establish an international standard for alpha-thrombin.

Since 1975 an International Standard for Thrombin of low purity has been used. While this standard was stable and of value for calibrating thrombins of unknown potency the need for a pure alpha-thrombin standard arose both for accurate calibration and for precise measurement of thrombin inhibitors, notably hirudin. An international collaborative study was undertaken to establish the potency and stability of an ampouled pure alpha-thrombin preparation. A potency of 97.5 international units (95% confidence limits 86.5-98.5) was established for the new alpha-thrombin standard (89/588) using a clotting-assay procedure. Stability data at various elevated temperatures indicated that the standard could be transported and stored with no significant loss of potency. Ampoules of lyophilised alpha-thrombin (coded 89/588) have been recommended as an International Standard for alpha-thrombin with an assigned potency of 100 international units per ampoule by the International Society for Thrombosis and Haemostasis (Thrombin and its Inhibitors Sub-Committee) in Barcelona, Spain in July 1990 while the Expert Committee on Biological Standardisation and Control of the World Health Organisation will consider its status at its next meeting in Geneva in 1991.

Drug Stability↗
PubMed1992

The genetic evolution of the envelope gene of simian immunodeficiency virus in cynomolgus macaques infected with a complex virus pool.

Two cynomolgus macaques were infected with a complex, but characterized, challenge stock of simian immunodeficiency virus (SIVmac251 32H). The polymerase chain reaction was applied in a temporal sequence analysis to determine the sequences of the gp120 region of the SIV env gene, which were present in the blood of both macaques at 1, 6, and 15 months postinfection (p.i.). At 1 month p.i. selected sequences, which had been present in the original virus challenge stock, were reisolated. At later times, new sequences emerged, which had not been detected in the original virus challenge stock. Changes in sequence were restricted to specific regions of gp120, notably those equivalent to V1, V2, V4, and V5 of HIV-1, but not V3. The diversity and the rate of appearance of new sequences in the V1 region suggest that genetic evolution occurs by mechanisms in addition to nucleotide substitutions. These results are discussed in relation to the role of the envelope protein in the generation of protective immunity against infection with immunodeficiency viruses.

Amino Acid Sequence↗
PubMed1992

The assessment of nucleotide sequence diversity by the polymerase chain reaction is highly reproducible.

The polymerase chain reaction (PCR) is often used to assess the diversity of viral nucleotide sequences present in various biological samples (e.g., blood and tissues). However, it is not clear how reproducible this approach may be. DNA was extracted from the peripheral blood lymphocytes of a macaque that had been infected, experimentally, with SIVmac251-32H 6 months previously. The nef gene was then amplified by the PCR on three separate occasions from this same template preparation. A panel of clones was prepared from the product of each PCR, the entire nef gene was sequenced and the sequences obtained compared with each other. Phenogram analysis revealed that within each panel the same degree of sequence diversity was observed between clones. Furthermore, when the sequences obtained from all three panels were compared, the overall sequence diversity observed was no greater than that observed for each panel individually. These data indicate that the analysis of sequence diversity in SIV 'quasi-species' populations by the PCR is reliable and, more important, reproducible.

Animals↗
PubMed1992

A collaborative study to examine the sensitivity and reproducibility of assays for the detection of DNA in biologicals derived from continuous cell lines.

This report describes the results of a collaborative study which was set up to examine the sensitivity and reproducibility of DNA assays performed by different laboratories. Fifteen laboratories analysed 12 samples containing different amounts of DNA and protein. The study revealed a high degree of variability between laboratories in determining the DNA content of the test samples.

Animals↗
PubMed1992

The Second International Standard for anti-poliovirus sera types 1, 2 and 3.

The Second International Standard for anti-poliovirus sera types 1, 2 and 3 was established by the WHO Expert Committee on Biological Standardization in 1991 on the basis of an extensive collaborative study. Nine laboratories from eight countries participated and all used neutralizing antibody assays. The standard is a human serum pool which contains antibodies to all three poliovirus types and replaces the three previously established monovalent standards which were all hyperimmune monkey sera. The standard was assigned an activity of 25 IU of anti-poliovirus serum (type 1) human: 50 IU of anti-poliovirus serum (type 2) human; and 5 IU of anti-poliovirus serum (type 3) human. The study also showed significant interlaboratory differences in relative potency are observed when human sera are compared to hyperimmune monkey sera. It was therefore recommended that National laboratory references are established from human sera.

Animals↗
PubMed1992

A collaborative study to assess the proficiency of laboratory estimates of potency of live measles vaccines.

A collaborative study was undertaken to assess the variability in estimates of the potency of measles vaccines. Overall a median variation of 2.0 log10 between estimates was observed. This was reduced to a median of 1.0 log10 when the potencies were expressed relative to a reference vaccine. A difference in the sensitivity between plaque assays and TCID50 assays was also reduced when relative potencies were used. The benefit of including a common reference preparation in vaccine assays was therefore demonstrated. For the vaccines assayed in this study, it was not necessary to use a measles reference of the same strain as the vaccines tested. We therefore recommend that measles vaccines be assayed against a single international reference preparation.

Analysis of Variance↗
PubMed1992

Comparability of poliovirus neutralizing antibody tests.

A serology panel was used to assess the comparability of results of poliovirus neutralizing antibody assays. Five laboratories from three countries provided results with seven in-house methods. A high degree of within-laboratory reproducibility was seen for all laboratories and methods, with 94% of results for repeat titrations within plus or minus one twofold dilution. Considerable differences in sensitivity between methods were, however, observed. The period of serum/virus incubation prior to inoculation of cells was shown by one laboratory to have a 10-fold effect on titres, and another laboratory showed that use of Sabin or wild-type challenge virus significantly influenced results for types 1 and 3. Expression of results as relative potencies abolished these difference due to method. The difference in sensitivity between laboratories for end-point titres (if one very sensitive method was excluded) was around fourfold for types 1 and 2, and ninefold for type 3. This range increased to 15-fold for type 2; and 20-fold for types 1 and 3 if the most sensitive method was included. Expression of results relative to a standard considerably improved agreement with a residual variation of around fourfold. Therefore, expression of results from serological studies, including vaccine trials, in International Units (i.e. relative to the new International Standard) will assure that comparisons between studies can be made with confidence.

Animals↗
PubMed1992

Role of horizontal genetic exchange in the antigenic variation of the class 1 outer membrane protein of Neisseria meningitidis.

The nucleotide sequences of the genes encoding the class 1 outer membrane protein of Neisseria meningitidis (PorA) from 15 meningococcal isolates have been examined. These strains, isolated over a number of years, represented a variety of serological types, clonal groups, and geographical locations. Analysis of the aligned nucleotide sequences showed that the known serological relationships between these proteins were not necessarily reflected throughout the nucleotide sequences of their genes. The uneven distribution of base substitutions, revealed by a comparison of the informative bases, suggested that these genes possessed a mosaic structure. This structure probably resulted from the horizontal transfer of DNA between strains and would have contributed to both the generation and the spread of novel antigenic variants of the protein. In addition, the nucleotide differences between porA genes from different strains were not consistent with the nucleotide sequence divergence of the whole chromosome, as indicated by pulsed-field gel electrophoresis (PFGE) fingerprinting techniques: some strains with divergent PFGE fingerprints shared porA genes with extensive regions of nucleotide sequence identity and, conversely, some strains with similar chromosome structures possessed porA genes with different nucleotide sequences and serological properties. This suggested that entire genes had been exchanged between strains. Given that the meningococcal class 1 OMP is a major component in novel vaccines, some of which are currently undergoing field trials, the potential of horizontal genetic exchange to generate antigenic diversity has implications for the design of such vaccines.

Antigenic Variation↗
PubMed1992

Molecular analysis of the serotyping antigens of Neisseria meningitidis.

Molecular approaches to the rapid analysis of the serotyping antigens of Neisseria meningitidis, the class 2 and 3 outer membrane proteins (OMPs), were developed, evaluated, and used to study 12 antigenic variants of these proteins. A primer set for the polymerase chain reaction (PCR) amplification of the genes encoding these antigens was devised. Low-stringency amplification of meningococcal chromosomal DNA with this primer set resulted in the amplification of two products from each strain, whereas at higher stringencies only one product was amplified in most strains. Southern hybridization techniques and restriction analyses were used to differentiate the PCR products amplified at high stringencies from strains expressing class 2 or class 3 OMPs; these PCR products were further characterized by the determination of their nucleotide sequences, confirming that they represented the amplified class 2 and class 3 OMP genes. Analyses of these and other nucleotide sequences enabled the construction of a phenogram illustrating the interrelationships between Neisseria OMP genes. The comparative analysis of deduced amino acid sequences revealed conserved and variable regions of the proteins; the latter probably correspond to surface loops on the protein and hence are potentially exposed to the immune system. Further analyses of the primary structures of these related porins from Neisseria species enabled construction of models of the secondary structure of these antigens and comparison of these models with those previously published. The methods reported in the present work are rapid reproducible procedures for the analysis of antigenic variants of these proteins.

Amino Acid Sequence↗
PubMed1991

Serological responses in volunteers to inactivated trivalent subunit influenza vaccine: antibody reactivity with epidemic influenza A and B strains and evidence of a rapid immune response.

A study of the immunogenicity of the inactivated trivalent subunit influenza vaccine for the 1989/90 season was performed in what proved to be an influenza epidemic year. One hundred student volunteers at The London Hospital Medical College participated in the study and the findings indicated that there was an excellent serological match between the epidemic strain of influenza A (H3N2) and the vaccine strain. Before vaccination, the geometric mean titre (GMT) to A/England/308/89, a representative H3N2 epidemic strain in the United Kingdom from the 1989/90 season, was 46. Post-vaccination the antibody levels rose and 99% of vaccinees had HI titres of greater than or equal to 40, the GMT being 131. The serological responses were also investigated against other circulating influenza A (H3N2 and H1N1) and B strains. Preliminary results of an evaluation of the rapidity of the immune response showed that in three of six subjects rises in HI antibody appeared within two days of vaccination.

Adult↗
PubMed1991

The 1st International Standard for anti-measles serum.

The 1st International Standard for anti-measles serum has been established on the basis of a collaborative study. There were four participating laboratories in four countries and three types of assay used. This standard has been assigned a potency of 5 IU anti-measles antibody per ampoule.

Antibodies, Viral↗
PubMed1990

A collaborative study to establish a standard for high molecular weight urinary-type plasminogen activator (HMW/u-PA).

An international collaborative study involving eleven laboratories located in eight countries was undertaken to establish an International Standard for high molecular weight urinary-type plasminogen activator (HMW/u-PA). The current International Reference Preparation (IRP code numbered 66/46) for urinary-type plasminogen activator (u-PA) or urokinase (see Nomenclature footnote) is a 66/34 molar ratio mixture of low molecular weight (LMW)--and high molecular weight (HMW)--u-PA's and is considered unsuitable as a standard for homogeneous preparations of HMW/u-PA. The putative standard for HMW/u-PA (code number, 87/594) was compared for potency in a clot lysis assay with the current IRP for u-PA (code number, 66/46) and a lyophilised preparation of single chain urinary-type plasminogen activator (SCuPA), the latter being used in the assay without prior activation by plasmin to its active two chain form (TCuPA). Both the proposed standard for HMW/u-PA (87/594) and the SCuPA compared in a statistically satisfactory manner in parallel line bioassays with the current IRP for u-PA (66/46), thus allowing potency estimates to be obtained for these two materials in relation to defined international units. Data from the eleven laboratories indicated that each ampoule of the proposed standard for HMW/u-PA contained 4,300 i.u. of activity and was stable for over 1 year at 4 degrees C. Most participants indicated that SCuPA expressed only a small amount of its activity without a prior activator step and this suggests that SCuPA assays need to be preceded by a plasmin activation step.(ABSTRACT TRUNCATED AT 250 WORDS)

Enzyme Stability↗