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Biomedical subjects

C M Turner

Publications and source records attributed to C M Turner.

At least 55 records · Page 3Linked to original sources
PubMed1993

Comparison of the effects of immune killing mechanisms on Trypanosoma brucei parasites of slender and stumpy morphology.

Trypanosoma brucei slender forms predominate over stumpy forms as the parasite population grows but at the peak of a parasitaemic wave and during remission of infection stumpy forms predominate. To determine whether this change in predominance might be caused by selective killing of slender forms, the fates of slender and stumpy form trypanosomes in two in vitro assays of immune-mediated killing were compared. Parasite populations in which > 90% of cells were of slender morphology were observed to be killed by antibody-dependent complement-mediated lysis approximately five times faster than populations in which < 15% of cells were slender and most were of intermediate or stumpy morphology. Quantification of the relationship between the proportion of slender forms in the population and the rate of lysis indicated that slender forms were killed approximately 7.3 times faster than other forms. In an opsonization assay, no differences were observed between slender and stumpy forms in the extent to which they attached to macrophages in an antibody-dependent manner. These results suggest that the change in proportions of slender and stumpy forms at the peak of a parasitaemic wave results from slender forms being more susceptible to complement-mediated killing as the antibody response develops.

Animals↗
PubMed1992

The relationship of variable antigen expression and population growth rates in Trypanosoma brucei.

The relationship between variable antigen type (VAT) expression and trypanosome growth rates was investigated. Growth rates in mice were compared between pairs of cloned trypanosome populations, each of which homogeneously expressed a different VAT. All three pairwise combinations of GUTats (Glasgow University Trypanozoon antigen types) 7.3, 7.4 and 7.5 were analysed twice and all three combinations of GUTats 8.2, 8.3 and 8.4 were compared once. The lines expressing different VATs were of the same passage history within each group. In a sensitive assay of relative growth, no significant differences were found in four of six experiments using GUTats 7.3, 7.4 and 7.5 or in one of three experiments using GUTats 8.2, 8.3 and 8.4. In the experiments in which differences were observed, the data were analysed further to compare the population doubling times of lines. These times differed by less than 10% in all cases. We conclude that variable antigen expression exerts a small (possibly negligible) effect on rates of trypanosome population growth.

Animals↗
PubMed1991

The dynamics of antigenic variation and growth of African trypanosomes.

Antigenic variation in African trypanosomes, which is a simple strategy for survival in the immune host, is rendered complex by its magnitude. For protection from nonspecific immunity and escape from specific immunity, each trypanosome is covered by a replaceable surface coat composed of the variant surface glycoprotein (VSG), which specifies the variable antigen type (VAT) of the trypanosome. Antigenic variation is the process by which the trypanosome switches from one coat to another. Here, David Barry and Michael Turner consider this phenomenon within the context of the course of trypanosome infection.

Journal Article↗
PubMed1991

The effects of genetic exchange on variable antigen expression in Trypanosoma brucei.

The inheritance of variant surface antigens in Trypanosoma brucei has been determined by identifying variable antigen types (VATs) in each of two cloned parental stocks and then examining the presence and abundance of these VATs in hybrid progeny produced when these stocks undergo genetic exchange during co-transmission through tsetse flies. Nine VATs have been identified from the repertoire of the parental stock STIB 247L and 5 VATs have been identified from the parental stock STIB 386AA; the identified VATs were exclusive to each stock. Their inheritance was elucidated using two assays. In the first, repertoire antisera (RAS) containing antibody specificities to many different VATs were raised in rabbits to the 2 parental stocks and 6 progeny clones. The presence of VAT-specific antibodies in these RAS was then determined by antibody-dependent complement-mediated lysis. In the second assay, the 2 parental stocks and 4 hybrid progeny clones were each independently transmitted through tsetse flies and VATs observed using VAT-specific antisera in indirect immunofluorescence of metacyclic trypanosomes and in bloodstream forms of fly-bitten mice. The results from both assays showed that (1) both metacyclic- and bloodstream-VATs were inherited into the progeny, (2) each hybrid progeny clone contained some VATs from both parents, (3) hybrids did not express all the VATs from either parent, (4) there was little apparent pattern as to which VATs had been inherited and which had not and (5) the VAT repertoires of the hybrid progeny appeared to be larger than those of the parents. In addition, two results indicated that control of VAT expression remains unaltered after genetic exchange.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Genetic exchange in Trypanosoma brucei.

The discovery of genetic exchange in African trypanosomes belonging to the Trypanosoma brucei group is an important development in our understanding of these organisms. Genetic exchange is a feature of major importance in relation to population structure and speciation. Furthermore, a convenient laboratory-based mating system would be of considerable value as a tool in trypanosomiasis research. It is now known that although cyclical development of trypanosomes within the tsetse fly does not require mating to occur, genetic exchange may take place under Conditions in which genetically distinct trypanosomes develop within the same fly. During the past few years there has been a considerable body of research on laboratory crosses, and a number of controversial and apparently contradictory models of the mechanism of genetic exchange and the ploidy of different life cycle stages have been proposed. In this article, Andy Tait and Mike Turner review the present state of knowledge regarding gene exchange in T. brucei, and attempt to reconcile the various observations and models available.

Journal Article↗
PubMed1990

The use of experimental artefacts in African trypanosome research.

When trypanosomes are removed from the field and maintained in laboratory conditions, phenotypic changes commonly occur such that the lines used by many investigators in routine work show several differences from the populations that affect humans and cattle in Africa. Whether these differences are important or irrelevant of course depends on the purpose of each particular experiment, but an awareness of what the differences are can be a useful aid in the interpretation of results. Furthermore, trypanosomes can be manipulated in the laboratory to possess particular characteristics that aid in the testing of hypotheses that are difficult to test using 'wild-type' trypanosomes. In this article, Mike Turner describes how some defined trypanosome lines have been created, how they differ from one another and several of their uses.

Journal Article↗
PubMed1990

Evidence that the mechanism of gene exchange in Trypanosoma brucei involves meiosis and syngamy.

All pairwise combinations of three cloned stocks of Trypanosoma brucei (STIB 247L, STIB 386AA and TREU 927/4) were co-transmitted through tsetse flies (Glossina morsitans) and screened for the production of hybrid trypanosomes. Clones of metacyclic and bloodstream trypanosomes from flies harbouring mature infections containing hybrid trypanosomes were established and screened for several isoenzyme and restriction fragment length polymorphisms. For each of the three combinations of parents, some progeny clones were observed to be of a phenotype and genotype indicating that genetic exchange had occurred during development of the trypanosomes in flies. These hybrid clones shared three salient features: (1) where the parents were homozygous variants the progeny were heterozygous, (2) where one of the parents was heterozygous, allelic segregation was observed and (3) the progeny clones were shown to be recombinant when two or more markers for which one of the parents was heterozygous were examined. These results are consistent with the progeny being an F1 in a diploid mendelian genetic system involving meiosis and syngamy. Our observations show that all possible combinations of the three stocks may undergo genetic exchange. A marker analysis of a series of clones each derived from single metacyclic trypanosomes showed that individual flies transmit a mixture of trypanosome genotypes corresponding to F1 progeny and to parental types, indicating that genetic exchange was a non-obligatory event in the life-cycle of the trypanosome. In addition, a preliminary analysis of the phenotype of procyclic stage trypanosomes derived from flies infected with two stocks, indicates that genetic exchange is unlikely to occur at this stage.

Alleles↗
PubMed1990

A comparison of multiplication rates in primary and challenge infections of Trypanosoma brucei bloodstream forms.

The hypothesis that division of Trypanosoma brucei slender bloodstream forms is dependent upon the availability of a host-derived growth factor has been tested by superimposing challenge doses of slender-form trypanosomes onto preexisting infections at a time during the primary infection when stumpy forms predominated. The challenge populations grew in the doubly-infected mice indicating that depletion of a putative growth factor by the expanding population of the primary infection had not prevented division of the trypanosomes although slight reductions in multiplication rates were observed. This effect was independent of the variable antigen type (VAT) of the trypanosomes and of their stock of origin.

Animals↗
PubMed1989

Gene exchange in African trypanosomes: frequency and allelic segregation.

The existence of a system of genetic exchange in Trypanosoma brucei is now established, but the frequency with which mating occurs and the mechanisms by which genes are exchanged are still unknown. This paper presents the results of a study of one pair of trypanosome stocks, which show that mating is a non-obligatory but frequent event in a life-cycle stage within the insect vector. Analysis of ten progeny clones using a total of eleven markers (iso-enzymes and DNA probes detecting restriction fragment length polymorphisms) has indicated that segregation of alleles occurs at five of these loci. The segregation patterns of a polymorphic EcoRI site in the maxi-circle of the kinetoplast DNA (kDNA) show that the progeny inherit one or other of the parental kDNA types. These results demonstrate that segregation of alleles occurs and that new combinations of alleles at different loci are generated in the progeny clones. The implications of these findings for defining the mechanism of gene exchange are discussed in relation to a simple mendelian genetic system involving meiosis and syngamy.

Alleles↗
PubMed1989

Genetic evidence that metacyclic forms of Trypanosoma brucei are diploid.

The hypothesis that metacyclic trypanosomes are haploid has been tested genetically. Five cloned stocks of Trypanosoma brucei (each having four known isoenzyme markers and six known restriction fragment length polymorphisms) have been independently transmitted through tsetse flies. Fifteen individual metacyclic organisms were taken from flies with mature cyclical infections and used to establish fresh clones. All the sub-clones from all the flies proved to be identical to the starting (parental) stocks, with respect to all the markers examined, including those markers which were heterozygous in the parental stocks. We conclude that metacyclic trypanosomes are diploid, and are not the product of an obligatory meiosis.

Animals↗
PubMed1989

High frequency of antigenic variation in Trypanosoma brucei rhodesiense infections.

Rates at which Trypanosoma brucei rhodesiense trypanosomes switch from expression of one variable antigen type (VAT) to that of another have been determined in cloned populations that have been recently tsetse-fly transmitted. Switching rates have been determined between several, specific pairs of VATs in each population. High rates of switching were observed in 2 cloned trypanosome lines, each derived from a separate cyclical transmission of the same parental stock and each expressing a different major VAT. Five estimates of the switching rate between one particular pair of VATs were consistently high (approximately 1 x 10(-3) switches/cell/generation). These high switching rates were similar both in bloodstream populations of mice and in populations confined to subcutaneously implanted growth chambers in mice, thus indicating that the interaction of the bloodstream population with other trypanosome populations in the lymphatics or extravascular sites in systemic infections did not influence the estimates of the rate of switching. Fourteen estimates were made of VAT-specific switching rates in bloodstream infections involving 8 combinations from among 6 VATs. Switching rate estimates were VAT-specific and showed considerable variation between different combinations of VATs--from 1.9 x 10(-6) to 6.9 x 10(-3) switches/cell/generation. The rates of switching to different metacyclic-VATs were, however, very similar. Summation of between 3 and 5 VAT-specific switching rate values in each of 4 experiments conducted in bloodstream infections has provided minimum estimates of the overall rate of antigenic variation: 2.0-9.3 x 10(-3) switches/cell/generation. These values are between 20 and 66,000-fold higher than previously published estimates.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Loss of variable antigen during transformation of Trypanosoma brucei rhodesiense from bloodstream to procyclic forms in the tsetse fly.

A pleomorphic line of Trypanosoma brucei rhodesiense expressing a single variable antigen was used to quantify the rate of loss of the surface coat from bloodstream forms transforming to procyclics in the tsetse fly, Glossina morsitans, and in in vitro culture. Loss of variable antigen occurred at similar rates in the crop and anterior portion of the midgut of tsetse flies and in in vitro culture, but in the posterior portion of the fly midgut it occurred 2-3 times faster. The posterior portion of the midgut is the most important site for transformation of bloodstream-form trypanosomes to procyclics, and the dynamics of at least one component of this process are therefore not accurately paralleled in vitro.

Animals↗
PubMed1988

Biology of African trypanosomes in the tsetse fly.

African trypanosomes present several features of interest to cell biologists. These include: a repressible single mitochondrion with a large mass of mitochondrial DNA, the kinetoplast; a special organelle, the glycosome, which houses the enzymes of the glycolytic chain; a surface coat of variable glycoprotein which enables the parasite to evade the mammalian host's immune response; and a unique flagellum-to-host attachment mechanism associated with novel cytoskeletal elements. Trypanosome development during the life cycle involves cyclical activation and repression of genes controlling these activities. Understanding the complexity of parasite development in the tsetse fly vector is especially challenging but may help to suggest new methods for the control of trypanosomiasis.

Animals↗
PubMed1988

An estimate of the size of the metacyclic variable antigen repertoire of Trypanosoma brucei rhodesiense.

A group of 27 variable antigen type (VAT)-specific monoclonal antibodies (McAbs) have been made against metacyclic forms of a cloned stock of Trypanosoma brucei rhodesiense. In combination, these labelled in immunofluorescence 99.3% of trypanosomes in salivary probes from tsetse flies. The 0.7% of unlabelled trypanosomes were believed to be uncoated forms. The ability of a mixture of antibodies to kill metacyclics in vitro by complement-mediated lysis, thus neutralizing their infectivity for mice, was tested. The antibody mixture consisted of 24 McAbs plus 3 VAT-specific rabbit antisera. In 12 replicate experiments this mixture of antibodies prevented infection of mice. Parallel controls showed that neutralization was probably antibody-mediated and VAT specific. However, we have not been able to repeat these results on a long-term basis; this may be due to a loss of neutralizing activity by one of the McAbs. The successful neutralization experiments indicate that the number of VATs in the metacyclic repertoire of one stock of T. b. rhodesiense is limited to at most 27.

Animals↗
PubMed1987

Prospective randomized controlled trial of urethral versus suprapubic catheterization.

Sixty-six patients requiring catheterization in the course of general surgical operations were randomly allocated into two groups. Of the 34 patients catheterized urethrally 16 developed urinary tract infections whereas of the 32 suprapubically catheterized patients only 2 developed an infection (P less than 0.001). Five patients required recatheterization after removal of their urethral catheters. There were no major complications associated with the use of suprapubic catheters. We propose that, when catheterization is required during a general surgical procedure, the suprapubic route is to be preferred.

Catheters, Indwelling↗