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Biomedical subjects

C R Howard

Publications and source records attributed to C R Howard.

At least 19 recordsLinked to original sources
PubMed1995

The ligase chain reaction distinguishes hepatitis B virus S-gene variants.

A novel method for the identification of hepatitis B virus (HBV) variants was developed. The ligase chain reaction (LCR) distinguished the sequences of two isolates from the Gambia showing a change at nucleotide 421 within the region coding for the surface protein a antigenic determinant. One sequence was derived from a child previously immunized with HBV vaccine, while the other, reported here for the first time, was from a chronic carrier. Nucleotide variations within the target sequence at, or up to 3 bases from the point of ligation inhibited the reaction. The LCR recognised variations in as little as 0.9 fmol DNA and will permit the rapid detection of HBV variants in molecular epidemiological studies.

Base Sequence↗
PubMed1995

The structure of hepatitis B envelope and molecular variants of hepatitis B virus.

Accumulated evidence in recent years has shown that the variation of hepatitis B virus (HBV) genomes may have profound implications for our understanding of hepatitis B pathogenesis and prevention. Attention has focused on areas of the outer envelope coded by the S gene which are involved in the induction of a protective neutralising antibody response, and mutations which directly affect the production of C gene products, one of which is considered as a target for immune T cells involved in virus clearance. This review highlights recent experimental data which emphasizes the role of such mutations in the establishment and maintenance of chronic HBV infections and focuses attention on the significance of HBV variants with respect to the expanding use of HBV vaccines for mass immunization.

Amino Acid Sequence↗
PubMed1995

Protection against morbillivirus-induced encephalitis by immunization with a rationally designed synthetic peptide vaccine containing B- and T-cell epitopes from the fusion protein of measles virus.

Synthetic peptides representing T- and B-cell epitopes from the fusion (F) protein of measles virus (MV) were tested for their ability to induce a protective immune response against intracerebral challenge with neuroadapted strains of MV and canine distemper virus (CDV) in mice. Of the panel of peptides tested, only a chimeric peptide consisting of two copies of a promiscuous T-cell epitope (representing residues 288 to 302 of MV F protein) synthesized at the amino terminus of a B-cell epitope (representing residues 404 to 414 of MV F protein) was able to induce a protective response against challenge with MV and CDV in inbred mice. The protective response induced by this peptide (TTB) was associated with a significant reduction in mortality, histological absence of acute encephalitis, and greatly reduced titers of virus in the brains of TTB-immune mice following challenge compared with the results for nonimmunized controls. A chimeric peptide comprising one copy of the T-cell epitope and one copy of the B-cell epitope (TB) did not induce a protective response. A comparison of the antibody responses induced by the two chimeras suggested that differences in protective efficacy following immunization may be a result of the higher affinity of the antibody induced by the TTB peptide than that of the antibody induced by the TB peptide. In addition, differences in the immunoglobulin G subclass of the antipeptide antibody responses were observed, and these may play a role in the differences in protection observed. These results indicate that appropriately designed synthetic peptides have potential as vaccines for the induction of cross-reactive protection against morbilliviruses.

Amino Acid Sequence↗
PubMed1994

A novel hepatitis B virus variant in the sera of immunized children.

A novel hepatitis B virus (HBV) variant was detected in the sera of two children in The Gambia, West Africa. The children had been immunized with plasma-derived vaccine and had developed antibody titres of 1448 international units x 10(-3) (mIU)/ml and 133 mIU/ml respectively against the hepatitis B surface antigen (HBsAg). Despite the protective levels of antibodies, HBV DNA was subsequently detected in both children. The complete surface (S) protein gene sequence demonstrated that this HBV isolate was closely related to the ayw4 subtype. However, five nucleotide changes were identified and two of these were unique to the Gambian isolate. One of these changes was within the region of the S gene coding for the immunodominant a determinant of the S protein. A unique nucleotide change from adenosine to guanosine at nucleotide 421 was found, resulting in an amino acid substitution at residue 141 from lysine to glutamic acid. Previous studies have shown that amino acids 141 to 146 are critical for binding to the protective anti-HBsAg antibodies. The presence of a variant HBV in these children suggests the emergence of a novel strain of HBV which can evade immune recognition. This has potential implications for HBV diagnosis and prophylaxis.

Amino Acid Sequence↗
PubMed1994

Infant formula distribution and advertising in pregnancy: a hospital survey.

A survey was conducted at a 526-bed community hospital in Rochester, New York, to determine the prevalence of formula advertising and distribution during pregnancy to 136 consecutive intrapartum patients. Women answered a questionnaire about their choice of infant feeding methods and prenatal exposure to formula advertising. Of those who received printed information on infant feeding, 78 percent reported that it was published by a formula company, and 65 percent recalled receiving offers for free formula during their pregnancy. The likelihood of having received such offers was the same in women who planned to breastfeed as in those who planned to formula feed. Thirty-eight percent of women obtained formula through a free offer before their infant's birth. Women who were privately cared for were more likely to have received offers for free formula (p < 0.001) than were women cared for in hospital-affiliated clinics. Ninety percent of women who received free formula prenatally reported their prenatal caregiver as a source of samples. Of samples that women obtained prenatally, 93 percent were from companies that advertise only indirectly through hospitals and physicians, whereas 7 percent were from companies that advertise directly to patients. The prevalence of formula company advertising during the prenatal care of women who deliver in this hospital is high. The continued participation of prenatal caregivers in promotion efforts of formula companies provides a negative or mixed message about the importance of breastfeeding and may be a barrier to its success.

Adult↗
PubMed1994

Acetaminophen analgesia in neonatal circumcision: the effect on pain.

OBJECTIVE: Recognizing the concerns about the use of local anesthesia in neonatal circumcision, a painful procedure usually performed without analgesia or anesthesia, we undertook a study of acetaminophen for pain management of this procedure. DESIGN: A prospective, randomized, double-blind, placebo-controlled, clinical trial of acetaminophen analgesia in 44 healthy full-term neonates undergoing circumcision was conducted. Beginning 2 hours before Gomco circumcision, neonates received either acetaminophen (15 mg/kg per dose, 0.15 mL/kg per dose) or placebo (0.15 mL/kg per dose) every 6 hours for 24 hours. Neonates were monitored intraoperatively for changes in heart rate, respiratory rate, and crying time. Postoperative pain was assessed at 30, 60, 90, 120, 360 minutes, and 24 hours using a standardized postoperative comfort scoring system. Feeding behavior was also assessed before and after circumcision by nursing observation. RESULTS: Neonates in both groups showed significant increases in heart rate, respiratory rate, and crying during circumcision with no clinically significant differences observed between the groups. Postoperative comfort scores showed no significant differences between the groups until the 360-minute postoperative assessment, at which time the acetaminophen group had significantly improved scores (P < .05). Feeding behavior deteriorated in breast- and bottle-fed neonates in both groups, and acetaminophen did not seem to influence this deterioration. CONCLUSIONS: This study confirms that circumcision of the newborn causes severe and persistent pain. Acetaminophen was not found to ameliorate either the intraoperative or the immediate postoperative pain of circumcision, although it seems that it may provide some benefit after the immediate postoperative period.

Acetaminophen↗
PubMed1993

Specificity of antibodies reactive with hepatitis B surface antigen following immunization with synthetic peptides.

The amino acid sequence 139-147 from hepatitis B surface antigen (HBsAg) has previously been shown to represent a B-cell epitope with potential as a component of a synthetic peptide vaccine against hepatitis B. In this paper, two regions of HBsAg which act as T-cell epitopes in inbred mice have been identified (residues 23-34 and residues 160-171). The ability of synthetic peptides representing these epitopes to provide help for the production of antibody against the 139-147 epitope has been assessed following their co-linear synthesis with the B-cell epitope and following co-immunization of the peptides in an uncoupled form. Both these strategies result in the induction of anti-peptide antibodies which specifically react with recombinant HBsAg. The results presented give further support to the concept that synthetic peptides representing appropriately chosen B- and T-cell epitopes from HBsAg could form the basis of a synthetic vaccine against hepatitis B.

Amino Acid Sequence↗
PubMed1992

Production of anti-peptide specific antibody in mice following immunization with peptides conjugated to mannan.

In order to investigate the usefulness of polysaccharides as carriers for the induction of antibody to synthetic peptides, peptides representing residues 139-147 of the surface antigen of hepatitis B and residues 129-140 of the pre-S2 region of the protein were coupled to mannan and dextran via an aminocaproic spacer molecule. Of the two conjugates studied, only mannan was useful as a carrier for the efficient production of anti-peptide antibodies.

Aminocaproates↗
PubMed1992

Analysis of the antigenic epitopes of hepatitis B surface antigen involved in the induction of a protective antibody response.

Vaccination with hepatitis B surface antigen (HBsAg) has shown that antibody directed against the common 'a' determinant of this antigen is protective against infection with hepatitis B virus (HBV). In this study the antigenic epitopes of the 'a' determinant have been analysed by competitive inhibition assays and by binding studies to synthetic peptides using a panel of monoclonal antibodies prepared against HBsAg, all of which are shown to recognise the common group determinant. One murine monoclonal antibody used in this study, RFHBs1, has been shown previously to block infectivity of HBV in susceptible chimpanzees ((1983) J. Med. Virol. 16, 89-95). This antibody bound to a cyclical synthetic peptide analogue of amino acids 124 to 137 of the major HBsAg polypeptide.

Antibodies, Monoclonal↗
PubMed1992

A topological model for hepatitis B surface antigen.

A model of hepatitis B surface antigen has been derived, based on extensive sequence analysis and biochemical data. The surface antigen sequences of the human, woodchuck, ground squirrel and duck hepadnaviruses were examined using hydrophobicity, hydrophobic moments, flexibility and secondary structure prediction. The helix phase diagram, which is a modified version of Eisenberg's hydrophobic moment plots and which specifically addresses the problem of transmembrane helices, was used to examine the predicted helices. In this model four transmembrane helices are predicted. The N and C termini and the second hydrophilic region, which bears the major B-cell antigenic determinants, are external. It is suggested that the transmembrane helices may pack to form a channel through the membrane and may also be involved in the mechanisms of cell entry. A significant difference between the duck hepadnavirus and the mammalian HBsAg sequences was found, hence care must be taken when extrapolating data between the duck and the human surface antigen.

Amino Acid Sequence↗
PubMed1991

Analysis of the glycoprotein gene of Tacaribe virus and neutralization-resistant variants.

We have previously generated neutralization-resistant variants of Tacaribe virus in the presence of a monoclonal antibody (MAb) specific for the envelope glycoprotein. The envelope glycoprotein precursor (GPC) genes of two variant viruses were sequenced following polymerase chain reaction amplification of a specific region of the Tacaribe virus S RNA, and compared with the GPC gene of the parental virus. Multiple nucleotide changes in the 3' half of the GPC gene were identified in the variants, suggesting that this part of the gene codes for the envelope glycoprotein of Tacaribe virus recognized by the MAb. Both variants showed unique amino acid substitutions up to 166 residues apart, suggesting that the most likely basis for neutralization resistance was a change in an epitope in which the critical residues are juxtaposed by conformation rather than by proximity in coding.

Amino Acid Sequence↗
PubMed1990

The affinity of anti-HBc antibodies in acute and chronic hepatitis B infection.

Antibodies to hepatitis B core antigen (anti-HBc) are found in the sera of all individuals infected with hepatitis B virus. A role for these antibodies has been suggested in determining the outcome of infection. In this study, the affinity of anti-HBc antibodies in asymptomatic virus carriers was compared with that of antibodies present in the sera of patients with chronic liver disease. Persistently infected individuals with no evidence of clinical disease were found to have anti-HBc antibodies of greater affinity, compared with the chronic liver disease group. Sera from patients with chronic hepatitis contained high levels of low-affinity antibody whereas antibody levels in asymptomatic carriers were significantly lower. These findings are discussed in relation to the predicted role of anti-HBc antibodies in mediating hepatitis B virus-related hepatocellular injury.

Acute Disease↗
PubMed1989

High level expression of genes cloned in phage lambda gt11.

Plasmid cloning vectors have been constructed which allow genes originally cloned in lambda gt11 to be expressed at a high level in Escherichia coli. They are based on the pEMBL and pUC vectors, with the genes transcribed from the lac promoter. The EcoRI site in the vector has been altered to be in the same reading frame as the site used for cloning in lambda gt11. Cloned proteins are expressed fused to a 2-kDa leader sequence containing a run of six Aparagine residues which considerably improves the stability of the recombinant proteins, but does not interfere with immunological assays. Using these vectors, the Mycobacterium leprae 18-kDa protein was expressed at 20 mg per litre of culture and constituted 15% of total cell protein.

Amino Acid Sequence↗
PubMed1988

IgG subclass-associated affinity differences of specific antibodies in humans.

Human IgG subclasses differ in their biologic functions and are restricted as specific antibodies to certain Ag. The basis for this restriction is unknown but in order to characterize it further, we obtained serum preparations containing one single subclass by using subclass-specific mAb in affinity chromatography. Subsequently we determined the affinity of antibodies in the four IgG subclasses for gp30/p25, a hepatitis B surface Ag (HBsAg) complex, for a nine-amino acid cyclical peptide representing residues 139 to 147 of HBsAg, and for a peptide representing residues 126 to 140 of the hepatitis B virus pre-S2 region and the relative avidity of IgG1 and IgG2 antibodies for purified pneumococcal polysaccharide type 3. Affinities to the HBsAg showed a clear pattern of decreasing affinity in the order IgG1 greater than IgG2 greater than IgG3 greater than IgG4 both in sera from vaccinated and from naturally infected individuals. The relative avidities of antibodies to the polysaccharide Ag had a reverse pattern, IgG2 greater than IgG1. In individuals with or without Ig H chain gene deletions where the anti-HBsAg response was restricted to one subclass, the affinity was similar to that observed for the same subclass in sera from individuals who in addition possessed high or low affinity antibodies of other subclasses.

Adult↗
PubMed1988

High-voltage electrical injury: acute pathophysiology.

A reproducible high-voltage electrical injury model was established in the primate using a new approach to energy administration, measurement instrumentation, and data acquisition. Patterns of current repartition and temperature generation were examined in 24 primates. The predominant current load was carried in muscle, which is the tissue group occupying the largest cross-sectional area. Highest temperature values observed were in muscles of small cross-sectional diameter and in tissues of high inherent resistance. Surgeons should be aware of the principles and the pattern of current distribution when performing early debridement and/or definitive coverage procedures.

Animals↗
PubMed1988

Morphogenesis of yellow fever virus 17D in infected cell cultures.

The morphogenesis of yellow fever virus replication was examined in infected Vero cell cultures. Penetration and uncoating occurred by endocytosis with the formation of coated vesicles, similar to that demonstrated for other enveloped and unenveloped viruses. Inclusion bodies associated with newly formed nucleocapsids were evident in the perinuclear region during the growth cycle. No evidence of RNA synthesis in the vicinity of the inclusion bodies was obtained by autoradiography, suggesting that genome replication and assembly of viral nucleocapsids occur at separate cytoplasmic sites. An excessive proliferation of membrane-bound organelles involving both vacuoles and endoplasmic reticula was the most striking feature of virus-infected cells late in infection. No morphological changes in the appearance of nuclei or mitochondria were detected. Virus release appeared to occur by movement of nascent virions through the proliferated endoplasmic reticula followed by exocytic fusion of virus-containing vesicles with the plasmalemma. A possible mechanism whereby the internal nucleocapsid acquires an outer envelope is discussed.

Animals↗