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Biomedical subjects

A Haworth

Publications and source records attributed to A Haworth.

31 records · Page 2Linked to original sources
PubMed1993

Data acquisition for linac based stereotactic radiosurgery.

In September 1991 a Philips Stereotactic Radiosurgery System (SRS 200) was installed in the Radiotherapy Department at Sir Charles Gairdner Hospital for use with an existing 6MV linear accelerator. The treatment planning software requires tables of Output Factors, Tissue Maximum Ratios (TMRs) and Off-Axis Ratios (OARs) for each specific linac/collimator set combination. Conventional techniques of acquiring radiation dose data for patient treatment planning were not suitable for the very small field sizes (5-30mm diameter) to be measured. Output Factors relative to a 100 x 100 mm field were measured using a large water tank and solid state diode detectors. The SRS 200 base frame which usually supports the special collimators could not be used with the tank in place and so a method for aligning the central axis of the beam, the SRS 200 collimators and diode was developed to improve the accuracy of measurement. TMRs were measured using two independent methods, similarly for the OARs. The first method of measuring TMRs made use of the large water tank and diode detectors. The second method employed the use of solid water phantom slabs seated on the base frame of the SRS 200. OARs were first measured with the solid water phantom slabs and diode; the second method made use of the technique of film dosimetry. Finally, a spherical water phantom was designed and built to check the total system accuracy. Agreement between sets of results measured by the independent methods was within 0.3% on average for TMRs and 0.25mm at the 50% dose level in most cases for the OARs.(ABSTRACT TRUNCATED AT 250 WORDS)

Australia↗
PubMed1990

Differential expression of the HLA class I multigene family by human embryonal carcinoma and choriocarcinoma cell lines.

We have studied the expression of both HLA class and the recently described HLA class I-like genes (HLA-E and HLA-6.0) in two human developmental tumor cell lines, that serologically could not be typed for HLA-A, -B, and -C. Evidence is presented that the teratocarcinoma Tera-2 stem cells express trace amounts of non-beta 2 microglobulin-associated classical HLA-A, -B, and -C Ag on their cell surface. The Jeg-3 human choriocarcinoma cells derived from fetal trophoblast express normal levels of surface beta 2 microglobulin associated with 45-kDa and 41-kDa H chains that display unique isoelectric points in IEF gels. The HLA-6.0 or HLA-E genes may encode the lower molecular mass component on Jeg-3 cells, because these genes express molecules of about 38 kDa and 41 kDa, respectively, when transfected to appropriate host cells. Transcripts homologous to the HLA-6.0 gene are found to be constitutively expressed in the Jeg-3 cells but not in Tera-2 cells, whereas HLA-E is not significantly transcribed in either cell line. Transcription of class I (HLA-A, -B, and -C) and class I-like (HLA-E and HLA-6.0) genes is up-regulated after treatment with IFN-gamma in Tera-2 cells, whereas the corresponding genes in Jeg-3 cells remain essentially unresponsive. The biologic role of trophoblast class I(-like) molecules in the context of the maternal acceptance of the fetal semiallograft is discussed.

Blotting, Northern↗
PubMedDate not supplied

Novel human MHC class I genes are expressed by tumour cell lines representing embryonic and extraembryonic tissues.

The expression of HLA class I(-like) genes was studied in two human developmental tumour cell lines representing embryonic (Tera-2) and extraembryonic (Jeg-3) origins. Neither cell line expresses polymorphic HLA-A, -B, -C antigens as determined by standard serological typing. Tera-2 cells express the HLA class I-like T cell system A (TCA) determinants; Jeg-3 cells are TCA negative. Northern blot analysis using an HLA class I alpha 3 domain specific probe revealed markedly reduced levels of HLA class I(-like) transcripts in both cell lines, which can be upregulated in Tera-2 cells by incubation with gamma interferon (gamma IFN). Immunoprecipitation studies with a large panel of HLA class I/beta-2 microglobulin (beta 2m) monoclonal antibodies (mAbs), detect low quantities of regular HLA class I heavy chains that are not associated with beta 2m on the surface of Tera-2 cells. In contrast, Jeg-3 cells express significant amounts of cell membrane beta 2m associated molecules of 41 and 45 kilodalton (kD). Screening of a Tera-2 cDNA library, yielded 30 clones that hybridize to a full length HLA class I cDNA probe. Sixteen have been characterized and represent HLA class I sequences, consistent with the haplotype of Tera-2. A similar screening of a Jeg-3 cDNA library isolated clones representing a single novel HLA-C-like sequence; this probably codes for the 45 kD cell surface molecules of Jeg-3. The 41 kD molecule may be encoded by the HLA-6.0 gene since this is constitutively expressed in Jeg-3 cells.

Choriocarcinoma↗
PubMedDate not supplied

Reactions to problems of drug abuse in Zambia.

Apart from the cannabis, the abuse of other drugs in Zambia was not considered a major problem in the past. There was obviously a lack of knowledge of the nature and extent of drug abuse. At present, limited information on drugs and drug abuse is incorporated into school curricula. When studies on drug abuse and on attitudes and reactions to abuse were initiated at the request of the United Nations Educational, Scientific and Cultural Organization (UNESCO) and because of rising public awareness, it became apparent that a drug abuse problem was beginning to develop in Zambia although it had not yet reached serious proportions. Such a situation demanded new preventive efforts which should include drug education, information and research components as well as a need to involve the people most concerned at all levels in both programme design and implementation. These components are described in this paper and it is emphasized that the planning of programmes in Zambia must form part of regional activities in cooperation with neighboring countries.

Child↗
PubMedDate not supplied

A preliminary report on self-reported drug use among students in Zambia.

Two studies of drug use among Zambian students are described; the first based on a sample of 336 secondary school students and the second on a sample of 1,836 students from a wide range of educational institutions. All these students belonged to a select group and their patterns of drug use may not be typical of the majority of youth who have not been able to continue with their education. Lifetime prevalence rates are examined and it is shown that while up to 10 per cent of the female students experimented with cannabis, only male students tended to become regular users. Apart from minor tranquillizers, the use of other drugs was relatively uncommon, and there were no reports of the use of morphine, heroin or cocaine. A connection between the frequency of reporting of problems and the drugs used indicates that there is a small proportion of vulnerable students who could be helped if detected early.

Adolescent↗
PubMedDate not supplied

The mutation status of PAX3 and p53 genes in medulloblastoma.

The p53 and PAX3 genes were examined by PCR, SSCP and DNA sequencing methods in 50 and 58 paraffinembedded medullablastoma tissues, respectively. Four novel mutations were identified among these samples in exon 5 of the p53 gene. Two tumours showed a G to A transition. One heterozygous mutation was located on codon 158 which changed the encoded amino acid from Arg (CGC) to His (CAC). Another was located on codon 174 and replaced AGG (Arg) with AAG (Lys). There was a single base deletion of guanine located on codon 160 in another two samples, causing a frameshift. This is the first study of mutation status of PAX gene in medulloblastoma wherein only one polymorphism was identified in the gene. The polymorphism changed codon 43 from GGC to GGT but both encoded glycine.

DNA-Binding Proteins↗