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Biomedical subjects

A Tait

Publications and source records attributed to A Tait.

At least 91 records · Page 5Linked to original sources
PubMed1991

Trypanosoma brucei rhodesiense: characterisation of stocks from Zambia, Kenya, and Uganda using repetitive DNA probes.

We have previously described a system for characterising the relationships between trypanosome stocks of the T.brucei group based on Southern blotting with repetitive DNA probes followed by cluster analysis of resultant banding patterns (G. Hide et al. Molec. Bioch. Parasitol. 39, 213-226, 1990). In this study, we extend this analysis to examine the relationships between trypanosome stocks isolated from major sleeping sickness foci in Zambia, Kenya, and Uganda. We show that the trypanosome strains responsible for disease in Zambia are quite distinct from those sampled from the Kenya/Uganda foci. Furthermore, the human serum resistant stocks isolated from the Kenya/Uganda foci which were isolated from man (or from animals) were found to form a tight group in the cluster analysis, while stocks isolated from nonhuman sources in the same area or stocks from elsewhere were found in separate groups. Thus, the human infective trypanosome strains found in these foci may have common origins and have, perhaps, arisen by clonal selection from a common source.

Animals↗
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↗
PubMed1991

Demonstration of Chlamydia trachomatis in colposcopic cervical biopsy specimens by an immunoperoxidase method.

A total of 31 cervical biopsy specimens were taken from 29 women attending a genitourinary medicine clinic, nine women (11 biopsy specimens) were known to have Chlamydia trachomatis cervicitis and 20 women were known to be free of chlamydial infection. The specimens were routinely processed to paraffin wax and stained by an anti-Chlamydia immunoperoxidase technique to localise the organisms. Of the 11 positive biopsy specimens three showed positive staining of elementary/reticulate bodies. In one case the surface endocervical cells showed large inclusions which were packed with chlamydial bodies. The diagnosis of chlamydial infection is difficult to make clinically and in routine cytological and histological specimens but immunoperoxidase staining can clearly identify C trachomatis inclusions in cervical biopsy specimens provided infection is severe.

Cervix Uteri↗
PubMed1990

Characterisation of an extrachromosomal DNA element from Theileria annulata.

Extrachromosomal nucleic acid elements are found in all organisms, commonly as organelle, viral or plasmid genomes. In this paper we describe the initial characterisation of a novel 6.5-kb linear, double-stranded extrachromosomal element from Theileria annulata, and a 2.6-kb RNA species. The DNA element is present in different stages of the life cycle and in different stocks of the parasite. Northern blots of total RNA isolated from different stages of the parasite, probed with the purified element, detect three major transcripts, of 1.45, 1.05 and 0.24 kb, present in all life-cycle stages examined. The possible origin and function of this element is discussed, together with its possible use as a transfection vector for the introduction of genes into protozoan cells.

Animals↗
PubMed1990

Stage-specific cuticular proteins of Ostertagia circumcincta and Ostertagia ostertagi.

In this study we have shown that NHS-biotin and I125-streptavidin can detect cuticular polypeptides of Ostertagia spp. The labelled polypeptide profile of intact nematodes is simple compared to the profile obtained by labelling homogenates. None of the major internal polypeptides are labelled and the subset of proteins labelled in intact nematodes appears to be mainly surface associated. The results presented here demonstrate that NHS-biotin may be used as a reagent for the analysis of surface polypeptides. The surface polypeptide profiles of the five major developmental stages (L1, L2, L3, L4 and adult) of Ostertagia circumcincta show a series of stage-specific molecules with no polypeptides common to all stages, indicating that the cuticle is a dynamic structure which changes throughout the life cycle. Similarily comparison of Ostertagia ostertagi L3 and L4 stage surface profiles showed that each stage is clearly distinct; comparison of these stages between the two species shows an overall similarity.

Animals↗
PubMed1990

The identification of Trypanosoma brucei subspecies using repetitive DNA sequences.

We describe the use of repetitive DNA probes to characterise the relationships between different stocks of African trypanosomes representing the subspecies of Trypanosoma brucei. Probes derived from the ribosomal RNA genes (coding region and nontranscribed spacer) and another repetitive DNA sequence were used to characterise trypanosome stocks by Southern blotting. Numerical taxonomy methods applied to the resulting restriction enzyme patterns were used to derive a dendrogram depicting the relationships between the stocks examined. We show that three groups of West African human infective stocks can be distinguished: firstly, a group containing exclusively T. b. gambiense; secondly, a group which is indistinguishable from animal isolates in West Africa; and thirdly, a single stock which is indistinguishable from East African T. b. rhodesiense. In addition, we observe that T. b. rhodesiense stocks from East Africa are indistinguishable from animal isolates from the same area. Finally, we show that a group of T. b. rhodesiense stocks, isolated from a 1978 sleeping sickness outbreak in Zambia, are probably derived from a single parasite strain, and that this strain is distinct from T. b. rhodesiense parasites from Kenya and Uganda.

Animals↗
PubMed1990

Developmental expression of a Theileria annulata merozoite surface antigen.

Culture of a lymphoblastoid cell line infected with the macroschizont stage of the protozoan parasite Theileria annulata at 41 degrees C induces differentiation to the next stage, the merozoite. We have demonstrated that this development results in the loss of monoclonal antibody epitopes associated with the macroschizont stage, and the appearance of epitopes associated with the piroplasm (the intra-erythrocytic stages). One of the monoclonals (5E1) was shown by immunoelectron microscopy to bind to the surface of heat-induced culture forms which had size and structural characteristics of the merozoite. The monoclonal was found to detect two polypeptides of 30 kDa and 25 kDa in extracts of piroplasms. The 30-kDa polypeptide was also detected in a merozoite extract, but was not detected in an extract derived from macroschizont-infected lymphoblastoid cells. We conclude that the heat-induced differentiation of T. annulata in vitro results in the expression of a 30-kDa molecule which is located at the surface of the merozoite, and discuss the potential of this molecule as a component in a subunit vaccine.

Animals↗
PubMed1990

Characterisation of protein kinase C like activities in Trypanosoma brucei.

Protein kinase activities in bloodstream and procyclic forms of Trypanosoma brucei have been partially purified and characterised. Cytosolic extracts were separated on DEAE-cellulose and assayed for the ability to phosphorylate histone in the presence of Ca2+ and diacylglycerol. Five peaks of activity were identified in bloodstream T. brucei and only three in procyclic lysates. One of the kinases present in bloodstream T. brucei shares may characteristics with mammalian protein kinase C. Further characterisation of the kinases using an in situ assay after separating proteins by isoelectric focussing confirmed that the kinases present in bloodstream and procyclic stages differed in properties and either bloodstream kinases are more stable or greater in number than procyclic kinases. A protein present in bloodstream T. brucei was shown by Western blot analysis to contain an epitope recognized by a monoclonal antibody raised against mammalian protein kinase C. We thus conclude that the protein kinases are differentially regulated between the two stages of the parasite and that the bloodstream stage has a protein kinase C homologue. The implications of these findings in relation to a cellular signalling pathway in trypanosomes is discussed.

Animals↗
PubMed1990

Genetic exchange in African trypanosomes.

African trypanosomes are important pathogens of humans and domestic animals, but little was known, until recently, of the genetic system of these parasites. Recent results demonstrate the existence of nonobligatory genetic exchange between different stocks of T. brucei. A number of models have been put forward for the mechanism of genetic exchange, including a fusion model with subsequent random loss of chromosomes and a more conventional mendelian system.

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

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

Genetic exchange and evolutionary relationships in protozoan and helminth parasites.

The study of genetic exchange systems and the use of genetic analysis has been relatively limited in parasites leading to considerable gaps in our basic knowledge. This lack of knowledge makes it difficult to draw firm conclusions as to how these systems evolved. An additional problem is also raised by the difficulties in defining evolutionary distances particularly with the unicellular protozoa, using classical ultrastructural and cytological criteria. While these difficulties have by no means been overcome, the use of rapid sequencing techniques applied to the ribosomal genes has allowed measurement of evolutionary distances, and considerable advances in our understanding of the genetic exchange systems in a few parasitic protozoa have recently been made. The conclusions from these recent sets of analyses are reviewed and then examined together in order to discuss the evolution of genetic exchange systems in parasitic protozoa. The evolutionary distances defined by ribosome sequence analysis show that parasites are an extremely divergent group, with distances which, in some cases, are orders of magnitude greater than the distances between mammals and fish; furthermore these studies suggest that the parasitic protozoa or their free-living ancestors are extremely ancient. These findings support the view that parasitism has occurred independently many times and that the parasitic life-style has been adopted by evolutionarily distinct groups. The recent observation of a non-obligatory genetic system in the diploid but evolutionary ancient kinetoplastid Trypanosoma brucei suggests that diploidy and meiosis are extremely old. The observation, in parasitic protozoa and helminths, that selfing or non-obligatory mating is a common feature suggests that these processes may be strategies to overcome the cost of meiosis. In this context, the question of what selective forces maintain genetic exchange is discussed.

Animals↗
PubMed1990

Theileria annulata: control measures, diagnosis and the potential use of subunit vaccines.

Theileria annulata is an important pathogen of domestic Bovidae across a broad region of the world with some 250 million cattle at risk. Our basic knowledge of the incidence and mortality is reviewed together with an outline of current control measures, including the use of acaricides, chemotherapy and attenuated cell line vaccines. The limitations and potential problems of these control measures are discussed and considered in relation to the use of a subunit vaccine. Research over the last ten years on the protective immune response to the disease in both laboratory and field studies suggests that a humoral immune response to the sporozoite could be protective although the primary protective response appears to be mediated by cytotoxic T-cells recognising the macroschizont-infected lymphocyte stage. Recent work on the study of protective antigens using recombinant DNA and hybridoma technologies is discussed together with the potential advantages and problems of such approaches. Possible future developments in our understanding of the immune response and the identification of the relevant antigens are considered in addition to the use of new techniques for diagnosis and the analysis of parasite diversity.

Animals↗
PubMed1990

Antitumor activity of methyl-4 H-1,2,4-benzothiadiazin-3-yl-carbamodithioate-S,S,-dioxide.

The antitumor activity of the methyl-6-chloro-4H-1,2,4-benzothiadiazin-3-yl-S-carbamothioate+ ++-S,S,-dioxide (1) and the methyl-4H-1,2,4-benzothiadiazin-3-yl-carbamodithioate-S,S-di oxide (2), has been evaluated. Compound 2 passed activity criteria for leukemia P388 and was also moderately active against transplanted mouse tumor L1210 leukemia and M5076 sarcoma.

Animals↗
PubMed1990

Carbamimidothioic acid phenylmethyl ester salts and their N,N'-tetramethyl derivatives as possible antimicrobial agents.

A series of carbamimidothioic acid phenylmethyl ester salts and their N,N'-tetramethyl derivatives were synthesized, many of which exert an interesting inhibiting action on Gram-positive and Gram-negative bacteria and also on fungi. This activity is noteworthy in view of the large number of strains antagonized; the (3,4,5-trichlorophenyl) methyl ester chloride of carbamimidothioic acid appeared to be the best term of the series. The possible influence on this activity of decomposition kinetics to the corresponding mercapto-derivatives was investigated and compared with that of a series of N,N'-tetramethyl derivatives of previously studied carbamimidothioic acid phenyl ester salts.

Anti-Bacterial Agents↗