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K Vickerman

Publications and source records attributed to K Vickerman.

At least 37 records · Page 2Linked to original sources
PubMed1986

The surface membrane of Leishmania mexicana mexicana: comparison of amastigote and promastigote using freeze-fracture cytochemistry.

The freeze fracture replica technique has been used to compare the plasma membranes of amastigote and promastigote stages of Leishmania mexicana mexicana with respect to intramembranous particle (integral protein) distribution and to beta-hydroxysterols content as revealed by the distribution of lesions induced by the polyene antibiotic filipin. Intramembranous particle (IMP) density was greater in promastigote than in amastigote plasma membranes. Intramembranous particles were more abundant in the protoplasmic face (PF) than in the exoplasmic face (EF) of promastigotes, but this situation was found to be reversed in amastigotes. Filipin-induced lesions in glutaraldehyde-fixed parasites indicated higher levels of beta-hydroxysterols in the amastigote than in the promastigote plasma membrane, and in the promastigote flagellar membrane than in the body membrane. Amphotericin B (a related polyene antibiotic used in chemotherapy of leishmaniasis) induced IMP aggregation in the PF of unfixed amastigotes but did not appear to influence sterol distribution as demonstrated by freeze-fracture of subsequently-fixed and filipin-treated organisms.

Amphotericin B↗
PubMed1986

Similarity in variable antigen type composition of Trypanosoma brucei rhodesiense populations in different sites within the mouse host.

Trypanosoma brucei rhodesiense subpopulations in different sites within the body of infected mice were isolated and enumerated on day 6 of cyclically transmitted infections. Most trypanosomes were in the blood vasculature and spleen but approximately 6% occurred in lymph nodes and about 9% were extravascular. Most of the extravascular trypanosomes were in the peritoneal and pleural cavities; significant numbers also occurred in the brain and kidneys. Six major variable antigen types (VATs) were detected by immunofluorescence using specific antisera and monoclonal antibodies. The prevalence of each VAT was essentially the same in subpopulations in the blood, mesenteric and inguinal lymph nodes, brain, kidneys and peritoneal and pleural cavities. This similarity of VAT composition in different subpopulations is probably caused by high rates of dynamic interchange of trypanosomes between sites. Extravascular trypanosomes, therefore, form a significant proportion of the total population in acute infections of mice but they do not appear to play any special role in the population biology of antigenic variation at this stage of infection.

Animals↗
PubMed1986

Three dimensional structure of the Leishmania amastigote as revealed by computer-aided reconstruction from serial sections.

Computer-aided reconstruction from serial sections has been used to analyse the 3-dimensional structure of entire amastigotes of Leishmania mexicana and to determine the number, arrangement and volume of each organelle. In two reconstructions, the lysosome-like 'megasomes' were the most numerous organelle, there being 34 in one amastigote, and they comprised as much as 15% of the total cell volume. In contrast, as few as 9 glycosomes were present, accounting for less than 1% of the cell volume. The unitary nature of the mitochondrion was confirmed and its complex basket-like structure was revealed. The spatial arrangement of the cell organelles is here displayed in stereo-pairs.

Animals↗
PubMed1986

Independent expression of the metacyclic and bloodstream variable antigen repertoires of Trypanosoma brucei rhodesiense.

The variable antigen repertoire expressed by metacyclic Trypanosoma brucei rhodesiense is not influenced by the anamnestic expression whereby the variable antigen type (VAT) ingested by a tsetse fly is present at high levels in early bloodstream populations of fly-infected mice. This has been demonstrated by feeding to Glossina morsitans a trypanosome line expressing a VAT which is normally a component of the metacyclic repertoire. The VAT did not constitute a significantly increased proportion of the resultant metacyclic population which would have occurred had anamnestic expression and metacyclic expression been linked. Five other metacyclic VATs were also present at control levels. We conclude that the mechanisms of expression of VATs in the fly and in the mammal are independently controlled.

Animals↗
PubMed1986

Kinetoplast DNA of Bodo caudatus: a noncatenated structure.

The kinetoplast DNA (kDNA) of trypanosomes and other parasitic members of the order Kinetoplastida is organized as a complex network containing thousands of catenated circular DNA molecules. We found that the kDNA of a free-living kinetoplastida, Bodo caudatus, exists as a noncatenated structure. The kDNA of B. caudatus represents about 40% of the total cellular DNA, and the major components of this DNA are large circles of 10 and 12 kilobases (kb). Our results indicate that these circles are analogous to trypanosome kDNA minicircles despite their large size and noncatenated form. The kDNA of B. caudatus also contains a minor component of 19 kb which is transcribed. The 19-kb molecules are probably analogous to the maxicircles of trypanosomes. The properties of the B. caudatus kDNA suggest that the catenated network structure of trypanosome kDNA is not required for maxicircle segregation during kinetoplast division or for the expression of the maxicircle genome.

Animals↗
PubMed1985

Kinetoplast DNA from Trypanosoma vivax and T. congolense.

We have analysed kinetoplast DNA (kDNA) of the African trypanosomes Trypanosoma vivax and T. congolense. The maxi-circles from these organisms resemble those of T. brucei in size, but only to a limited extent in sequence as judged from restriction enzyme digests and DNA X DNA hybridization. The kDNA networks of T. vivax have three distinguishing features: they contain the highest maxi-circle concentration of any kDNA (at least twice that of T. brucei); they contain the smallest mini-circles (465 bp) yet found thus far and the width of the kDNA nucleoid in thin sections is correspondingly small (55 nm against 91 nm for T. brucei); they contain a substantial fraction of mini-circle dimers.

Animals↗
PubMed1985

Neutralization of individual variable antigen types in metacyclic populations of Trypanosoma brucei does not prevent their subsequent expression in mice.

The Trypanosoma brucei metacyclic population in the salivary glands of the tsetse fly displays a characteristic set of variable antigen types (VATs) which represents only a restricted part of the parasite's total VAT repertoire. After introduction into the mammalian host by fly bite, the metacyclics transform into bloodstream forms which retain expression of the metacyclic VATs. Specific antibodies, both polyvalent and monoclonal, have been used to neutralize separately 4 individual VATs from metacyclic populations. Control experiments and visual observation confirmed lysis of each VAT. On injection of the surviving trypanosomes, after washing, into mice each neutralized VAT was nevertheless expressed within a few days. Simultaneous neutralization of 2 metacyclic VATs which usually switch to one another in bloodstream infections did not prevent expression of either on subsequent injection into mice. Expression of neutralized VATs was not influenced by the antigenic composition of the population originally ingested by the tsetse fly. Metacyclic forms and their immediate successors thus appear to switch rapidly to expression of other metacyclic VATs in bloodstream populations.

Animals↗
PubMed1985

Differentiation in Trypanosoma brucei: host-parasite cell junctions and their persistence during acquisition of the variable antigen coat.

Acquisition of the variable antigen-containing surface coat of Trypanosoma brucei occurs at the metacyclic stage in the salivary glands of the tsetse fly vector. The differentiation of the metacyclic trypanosome in the gland has been studied by scanning electron microscopy and by transmission electron microscopy of thin sections and freeze-fracture replicas. The uncoated epimastigote trypanosomes (with a prenuclear kinetoplast) divide while attached to the salivary gland epithelium brush border by elaborate branched flagellar outgrowths, which ramify between the host cell microvilli and form punctate hemidesmosome-like attachment plaques where they are indented by the microvilli. These outgrowths become reduced as the epimastigotes transform to uncoated trypomastigotes (with postnuclear kinetoplast), which remain attached and capable of binary fission. The flagellar outgrowths disappear but the attachment plaques persist as the uncoated trypomastigotes (premetacyclics) stop dividing and acquire the surface coat to become 'nascent metacyclics'. Coat acquisition therefore occurs in the attached trypanosome and not, as previously believed, after detachment. Coating is accompanied by morphological changes in the glycosomes and mitochondrion of the parasite. Freeze-fracture replicas of the host-parasite junctional complexes show membrane particle aggregates on the host membrane but not on the parasite membrane. It is suggested that disruption of the complex occurs when maximum packing of the glycoprotein molecules has been achieved in the trypanosome surface coat, releasing the metacyclic trypanosome into the lumen of the gland.

Animals↗
PubMed1984

Cytotoxicity of monoclonal antibodies to Trypanosoma brucei.

Monoclonal antibodies (McAbs) were raised against Metacyclic Variable Antigen Types (M-VATs) of the AnTAR 1 and ETAR 1 serodemes of Trypanosoma brucei. Two dominant M-VATs, one from each serodeme, were labelled by two of the McAbs using the indirect immunofluorescence technique. These McAbs were of the IgM class, and labelled exposed epitopes on living trypanosomes. They showed lytic activity in vitro towards their respective homologous VAT trypanosomes, both in the presence and absence of complement. In vivo, the McAbs promoted lysis and clearance of trypanosomes from the bloodstream of infected mice. Prevention of reinfection with trypanosomes expressing the same VAT was conferred by the McAbs.

Animals↗
PubMed1981

Absence of a surface coat from metacyclic Trypanosoma vivax: possible implications for vaccination against vivax trypanosomiasis.

Trypomastigotes attached to the wall of the hypopharynx in tsetse flies infected with Trypanosoma vivax are believed to represent the true metacyclic stage of this trypanosome. Electron microscopy demonstrates that attachment is mediated by hemidesmosome-like junctions along the flagellar membrane and that none of the trypomastigotes, either attached or free in the hypopharynx lumen, possesses a surface coat comparable with that on the metacyclics of T. brucei and T. congolense and on the bloodstream stages of all salivarian trypanosomes. As the variable antigen of bloodstream and metacyclic T. brucei is located in the surface coat, the absence of the coat from metacyclic T. vivax suggests that the mechanism of antigenic variation in this species may be somewhat different from that of antigenic variation in T. brucei, and that vaccination of cattle against T. vivax may prove a simpler proposition than vaccination against T. brucei.

Animals↗
PubMed1981

Absence of detectable alteration in the kinetoplast DNA of a Trypanosoma brucei clone following loss of ability to infect the insect vector (Glossina morsitans).

A monomorphic bloodstream population of Trypanosoma brucei EATRO 1244 was derived from a cloned pleomorphic parental population by 77 rapid passages through mice. Loss of pleomorphism was accompanied by increased virulence of trypanosomes towards the mammal, by loss of ability to infect the tsetse fly, Glossina morsitans, loss of ability to transform to the procyclic stage in vitro at 26 degrees C, and by loss of oligomycin-sensitive ATPase activity in trypanosome homogenates. No differences in the maxicircle component of the kinetoplast DNAs (kDNA) of the two populations were detected by electron microscopy of kDNA network spreads or by electrophoretic analysis of restriction endonuclease digests. It appears, therefore, that loss of transmissibility and associated ability of the trypanosomes to activate the mitochondrion need not necessarily be the result of deletions in the mitochondrial (maxicircle) genome. We suggest that point mutations in critical mitochondrial genes, undetectable using out methods, or mutations of nuclear genes coding for important mitochondrial enzymes, may account for the observed changes in phenotype.

Animals↗
PubMed1981

Respiration of Leishmania mexicana amastigotes and promastigotes.

Promastigotes of Leishmania mexicana mexicana recently derived from amastigotes by transformation in vitro respired at a rate (17 nmol O2/min per 10(8) parasites) 4-5 times higher than that of amastigotes, but when the difference in cell protein content between the two preparations was taken into account the rates were not significantly different (32 nmol O2/min per mg protein). The respiration of both amastigotes and promastigotes was sensitive to cyanide, azide, antimycin A, 2-n-heptyl-4-hydroxyquinoline-N-oxide and high concentrations of amytal, but insensitive to rotenone and salicyl-hydroxamic acid, indicating that the two developmental forms possess a similar cytochrome-containing respiratory chain. D-Glucose and non-esterified fatty acids stimulated promastigote respiration and amastigote transformation to promastigotes in vitro; possibly these substances are important exogenous energy substrates for both forms of the parasites. Amino acids (incuding L-proline) and proteins did not appear to be used as energy substrates. The respiration rate of promastigotes was found to rise significantly upon continued sub-culture in vitro; at the same time cell size and protein content increased.

Amino Acids↗
PubMed1981

A quick, simple method for purifying Leishmania mexicana amastigotes in large numbers.

A rapid method for the bulk isolation of purified Leishmania mexicana mexicana amastigotes from parasite-induced lesions in experimentally infected mice is described. The procedure includes purification steps based on differences in net cell charge, lysis susceptibility and buoyant density between parasite and host cells. Yields of up to 2 x 10(10) untransformed amastigotes with minimal contamination with host cells and cell debris can be obtained. At least 90% of the purified amastigotes are viable as judged by light and electron microscopy, the staining of their lysosomes with acridine orange, their ability to transform to promastigotes and their infectivity to macrophages in vivo and in vitro.

Animals↗
PubMed1979

Detection of multiple variable antigen types in metacyclic populations of Trypanosoma brucei.

The identification of antigen types in tsetse salivary gland metacyclic populations of Trypanosoma brucei requires the production of monospecific antisera to the corresponding bloodstream variable antigen types. Monospecific antisera against clones from cyclically transmitted populations are difficult to prepare, however, owing to the antigenic lability of such clones. This problem has been overcome by isolating an antigenically stable clone from a syringe-infected rabbit at a time when its serum showed incipient activity towards metacyclic trypanosomes. Monospecific antisera raised against this clone reacted with up to 20% metacyclics in trypanolysis and immunofluorescence tests, confirming that a clone-derived metacyclic population of T. brucei is heterogeneous with respect to variable antigen type.

Animals↗
PubMed1978

Antigenic variation in trypanosomes.

In its mammalian host, Trypanosoma brucei is able to change the antigenic character of its glycoprotein surface coat and so evade the host's immune response. This phenotypic change seems to occur spontaneously in 1 in 10,000 individuals but is not due to genetic mutation: host antibody is not necessary for its induction but plays a selective part in bringing about the gross changes in parasite numbers and antigenic character observed in the bloodstream by destroying the main component of what is actually a heterogeneous population. The infecting trypanosome population injected into the mammalian host by the tsetse fly vector may also be heterogeneous. Such heterogeneity complicates plans to vaccinate cattle and people against the African trypanosomes based on the premise that the metacyclic trypanosomes of a clone bear the same surface antigen.

Animals↗