Support person interventions to increase use of quitline services among racially diverse low-income smokers: A pilot study

INTRODUCTION

Social support from nonsmokers may have a role in prompting smokers to use evidence-based cessation treatment. Prior studies found that an intervention for nonsmoking support persons (SPs) was effective for promoting smokers' use of free, state quitline services. This pilot study adapted and assessed feasibility of this intervention for a racially diverse, low-income population.

METHODS

Single group, non-randomized design enrolling SP-smoker dyads with low income status enrolled in one of three study "waves" of 10 pairs each. Participants were recruited using flyers and in-person outreach methods. The SP intervention included a 1-session coaching call and written materials; study waves 2 and 3 also included text messaging and a monetary incentive for smokers who used quitline services. Using content analysis, the intervention was iteratively adapted based on SP feedback. Baseline measures assessed socio-demographics, dyad and tobacco use characteristics. Follow-up assessments were conducted among SPs at 1-month follow-up and among smokers at 3-months follow-up. Feasibility indicators were recruitment, retention, and SP intervention acceptability and adherence. Secondary outcomes were smokers' use of any quitline service verified by quitline staff and 7-day, point prevalence, biochemically verified smoking abstinence at 3 months.

RESULTS

Recruitment of 30 dyads was feasible; in-person recruitment methods were the most successful. SPs who completed follow-up assessments found the intervention acceptable, suggesting only minor content modifications, and they perceived the quitline information as novel. But the study had some feasibility challenges (e.g., SP coaching call completion: 60% and SP study retention: 53%). At 3 months, 2 smokers (7%) had used any quitline service and 13% were biochemically confirmed smoking abstinent.

CONCLUSIONS

This pilot study demonstrated feasibility of recruiting SP-smoker dyads from diverse, low-income communities. While the intervention was well received, its delivery was not feasible in this population. Results suggest that further consumer adaptation of the intervention is needed among both SPs and smokers.

Changes in Quitline Caller Characteristics During a National Tobacco Education Campaign

INTRODUCTION

The Centers for Disease Control and Prevention launched the first federally-funded national tobacco education campaign, "Tips From Former Smokers" (Tips), in 2012. This study examined changes in quitline caller characteristics, including demographics and smoking-related behaviors before and during the Tips campaign.

METHODS

Using quitline data from 20 U.S. states and the District of Columbia, we examined characteristics of 76,933 callers during the Tips campaign (March 19, 2012 to June 10, 2012) compared to 44,710 callers from a similar time period in 2011 (March 21, 2011 to June 12, 2011). We also examined whether characteristics differed by self-reported awareness of Tips during the campaign in 13 quitlines that added a Tips awareness question. Group differences were assessed using chi-square and t tests, adjusted for clustering by state.

RESULTS

Overall, few meaningful differences in caller characteristic existed, indicating broad reach of the Tips campaign across demographic groups. Compared with 2011, the number of callers during Tips increased by 72% and callers were twice as likely to hear about the quitline through television media. The proportion of uninsured callers was slightly higher during the Tips campaign than in 2011. Persons aware of the campaign were slightly more likely to be non-Hispanic Blacks, younger than age 55 years, and uninsured than those unaware of the campaign.

CONCLUSIONS

The Tips campaign increased the reach of quitline services to the general population of smokers, with increases across all demographic and tobacco use groups, but particularly among those who were uninsured. Such campaigns have the potential to increase access to cessation services for the uninsured.

Intermediate cessation outcomes among quitline callers during a national tobacco education campaign

INTRODUCTION

From March 19 through June 10, 2012, the Centers for Disease Control and Prevention launched the first federally funded National Tobacco Education Campaign: Tips From Former Smokers (Tips). This study examined the campaign's impact on quitline callers' intermediate cessation outcomes.

METHODS

We used quitline data from 23 states to examine changes in enrollment, service utilization, quit attempts, and self-reported quitting for 7 days or longer during Tips versus a similar time period in 2011. We used multivariate models to examine the relationship between Tips exposure (measured as gross rating points [GRPs]) and cessation outcomes during the campaign in 2012. We also assessed whether the Tips campaign's impact differed by state tobacco control funding.

RESULTS

Compared with similar weeks in 2011, the number of quitline callers and callers who received counseling and/or nicotine replacement therapies increased by 88.6% (48,738 in 2011 vs. 91,911 during Tips) and 70.8% (40,546 in 2011 vs. 69,254 during Tips), respectively. Greater numbers of callers reported having made 24-hr quit attempts or quitting for 7 days or longer during the campaign. Higher Tips campaign GRPs were positively associated with quit attempts and with quitting for 7 days or longer among persons from states with higher tobacco control funding. In states with lower funding, the highest GRP group (2,000+ GRPs) had lower levels of cessation compared with the middle GRP group (1,200-1,999 GRPs).

CONCLUSIONS

An evidence-based national tobacco education campaign with adequate reach and frequency can lead to substantial increases in quitline use and, to a lesser degree, intermediate cessation outcomes.

Communication and frightening behavior among couples with past and recent histories of physical marital aggression

The present study compares observed communication and couples' reports of husbands' frightening behaviors among couples with no history of husbands' physical marital aggression, a past history of such aggression, and recent history of such aggression. Ninety community couples reported on husbands' physical marital aggression during two visits to the lab, approximately 1.5 years apart. During the second visit, we videotaped couples' discussions of conflictual marital issues. Poor communication, as indexed by high hostility, low problem-description and low warmth, characterized couples with recent aggression, as compared to past aggression or no aggression. Husbands' frightening behavior characterized the couples with either recent or past aggression, compared to no aggression. In addition, for couples who had experienced severe aggression, the rates of husbands' frightening behavior were similar regardless of whether husbands persisted, reduced or desisted in the severe aggression. Discussion addresses possible reasons that reductions and desistance in husbands' aggression may be associated with more positive communication patterns but with continued reports of frightening behavior.

Estimating the growth potential of the soil protozoan community

We have developed a method for determining the potential abundance of free-living protozoa in soil. The method permits enumeration of four major functional groups (flagellates, naked amoebae, testate amoebae, and ciliates) and it overcomes some limitations and problems of the usual 'direct' and 'most probable number' methods. Potential abundance is determined using light microscopy, at specific time intervals, after quantitative re-wetting of air-dried soil with rain water. No exogenous carbon substrates or mineral nutrients are employed, so the protozoan community that develops is a function of the resources and inhibitors present in the original field sample. The method was applied to 100 soil samples (25 plots x 4 seasons) from an upland grassland (Sourhope, Southern Scotland) in the UK. Median abundances for all four functional groups lie close to those derived from the literature on protozoa living in diverse soil types. Flagellates are the most abundant group in soil, followed by the naked amoebae, then the testate amoebae and ciliates. This order is inversely related to typical organism size in each group. Moreover, preliminary evidence indicates that each functional group contains roughly the same number of species. All of these observations would be consistent with soil having fractal structure across the size-scale perceived by protozoa. The method described will be useful for comparing the effects on the soil protozoan community of different soil treatments (e.g. liming and biocides).

Protozoan paradigms for cell biology

This article introduces a miniseries of three commentaries on parasite cell biology. The reviews were written as a tribute to Keith Vickerman FRS on his retirement as Regius Professor of Zoology at the University of Glasgow and are based on presentations given at a symposium held to honour his pioneering work in the field. On page 2799 of this issue, Michael Ferguson reviews the structure and function of GPI anchors, and the contributions that studies of trypanosomes have made. In subsequent issues, James Alexander, Abhay Satoskar and David Russell discuss Leishmania species as models of intracellular parasitism, and Michael Turner presents a holistic view of antigenic variation in Trypanosoma brucei infections.

In vitro cultivation and developmental cycle in culture of a parasitic dinoflagellate (Hematodinium sp.) associated with mortality of the Norway lobster (Nephrops norvegicus) in British waters

Dinoflagellates are common and often important parasites of aquatic organisms, but their developmental cycles are poorly known and have not been established in in vitro culture. The parasitic dinoflagellate (Hematodinium sp.) associated with mortality of the Norway lobster (Nephrops norvegicus) in British waters has been cultivated in vitro in 10% foetal calf serum in a balanced Nephrops saline. In culture the parasite undergoes a characteristic cycle of development. Circulating sporoblasts from the host's haemolymph in vitro generate 2 kinds of flagellated uninucleate dinospore, macrospores and microspores, either of which will, after 5 weeks in fresh medium, germinate to produce multinucleate unattached filamentous trophonts. These trophonts multiply by fragmentation and growth and may be serially subcultured in this form, at 2 week intervals, indefinitely. If not subcultured, the filamentous trophonts give rise to colonies of radiating filaments ('gorgonlocks') which subsequently attach to the substratum to form flattened web-like 'arachnoid' multinucleate trophonts. Arachnoid trophonts become arachnoid sporonts when they synthesize trichocysts and flagellar hairs and may give rise to secondary arachnoid sporonts or to dinospores which initiate a new cycle.

Preface to Immune effector mechanisms in parasitic infections, a Discussion held at The Royal Society on the 19 and 20 February 1997

Preface to the published proceedings of Immune effector mechanisms in parasitic infections, a Discussion held at The Royal Society on the 19 and 20 February 1997, organized and edited by F. Y. Liew and K. Vickerman.

Presence of apicomplexan-type micropores in a parasitic dinoflagellate, Hematodinium sp

Structures resembling apicomplexan micropores were found by transmission electron microscopy in in vitro-cultured and in in vivo forms of the parasitic dinoflagellate Hematodinium sp. from crustacean hosts. Uptake of colloidal gold indicated a cytostomal function for the micropores.

The evolutionary expansion of the trypanosomatid flagellates

The trypanosomatids combine a relatively uniform morphology with ability to parasitise a very diverse range of hosts including animals, plants and other protists. Along with their sister family, the biflagellate bodonids, they are set apart from other eukaryotes by distinctive organisational features, such as the kinetoplast-mitochondrion and RNA editing, isolation of glycolysis enzymes in the glycosome, use of the flagellar pocket for molecular traffic into and out of the cell, a unique method of generating cortical microtubules, and bizarre nuclear organisation. These features testify to the antiquity and isolation of the kinetoplast-bearing flagellates (Kinetoplastida). Molecular sequencing techniques (especially small subunit ribosomal RNA gene sequencing) are now radically reshaping previous ideas on the phylogeny of these organisms. The idea that the monogenetic (MG) trypanosomatids gave rise to the digenetic (DG) genera is losing ground to a view that, after the bodonids, the African trypanosomes (DG) represent the most ancient lineage, followed by Trypanosoma cruzi (DG), then Blastocrithidia (MG), Herpetomonas (MG) and Phytomonas (DG), with Leptomonas (MG), Crithidia (MG), Leishmania (DG) and Endotrypanum (DG) forming the crown of the evolutionary tree. Vast genetic distances (12% divergence) separate T. brucei and T. cruzi, while the Leishmania species are separated by very short distances (less than 1% divergence). These phylogenetic conclusions are supported by studies on RNA editing and on the nature of the parasite surface. The trypanosomatids seem to be able to adapt with ease their energy metabolism to the availability of substrates and oxygen, and this may give them the ability to institute new life cycles if host behaviour patterns allow. Sexual processes, though present in at least some trypanosomatids, may have played only a minor part in generating diversity during trypanosomatid evolution. On the other hand, the development of altruistic behaviour on the part of some life cycle stages may be a hitherto unconsidered way of maximising fitness in this group. It is concluded that, owing to organisational constraints, the trypanosomatids can undergo substantial molecular variation while registering very little in the way of morphological change.

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.

The glycosomes of trypanosomes: number and distribution as revealed by electron spectroscopic imaging and 3-D reconstruction

Computer-aided 3-D reconstruction of trypanosomes from 0.35-micron-thick sections imaged on the Zeiss 902 electron microscope are being used to study the dynamics of cell organization. Segregation of glycolytic enzymes into glycosomes raises questions concerning the distribution and biogenesis of these organelles. Direct counts of glycosomes from Trypanosoma evansi indicate 30-40 per cell and for the closely related T. brucei, 65 per cell. These figures contrast with the estimates of others who have used model-based morphometric methods to obtain a value of 230 per cell.

Multinuclear forms in a dyskinetoplastic strain of Trypanosoma evansi in mice

The production of short stumpy and multinuclear trypanosomes in a Chinese strain of dyskinetoplastic Trypanosoma evansi maintained in rabbits and mice is described. Production of multinuclear trypanosomes was increased following passage through a reptile (gecko), in which the trypanosomes did not multiply, and transfer back to mice. The multinuclear trypanosomes showed more nuclei than flagella indicating that disruption of the normal cell cycle had taken place and not simply inhibition of cleavage. A Chinese kinetoplastic T. evansi treated similarly rarely produced stumpy or multinuclear forms.

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.

Trypanosome sociology and antigenic variation

Survival of the trypanosome (Trypanosoma brucei) population in the mammalian body depends upon paced stimulation of the host's humoral immune response by different antigenic variants and serial sacrifice of the dominant variant (homotype) so that minority variants (heterotypes) can continue the infection and each become a homotype in its turn. New variants are generated by a spontaneous switch in gene expression so that the trypanosome puts on a surface coat of a glycoprotein differing in antigenic specificity from its predecessor. Homotypes appear in a characteristic order for a given trypanosome clone but what determines this order and the pacing of homotype generation so that the trypanosome does not quickly exhaust its repertoire of variable antigens, is not clear. The tendency of some genes to be expressed more frequently than others may reflect the location within the genome and mode of expression of the genes concerned and may influence homotype succession. Differences in the doubling time of different variants or in the rate at which trypanosomes belonging to a particular variant differentiate into non-dividing (vector infective) stumpy forms have also been invoked to explain how a heterotype's growth characteristics may determine when it becomes a homotype. Recent estimations of the frequency of variable antigen switching in trypanosome populations after transmission through the tsetse fly vector, however, suggest a much higher figure (0.97-2.2 x 10(-3) switches per cell per generation) than that obtained for syringe-passed infections (10(-5)-10(-7) switches per cell per generation) and it seems probable that most of the variable antigen genes are expressed as minority variable antigen types very early in the infection. Instability of expression is a feature of trypanosome clones derived from infective tsetse salivary gland (metacyclic) trypanosomes and it is suggested that high switching rates in tsetse-transmitted infections may delay the growth of certain variants to homotype status until later in the infection.

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.

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.

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.

The requirement for epimastigote attachment during division and metacyclogenesis in Trypanosoma congolense

In cultures of tsetse proboscis stages during the development of Trypanosoma congolense, attached epimastigote forms multiply and give rise to free nondividing metacyclic trypanosomes. Prevention of attachment by shaking the cultures or by providing a polypropylene substratum does not inhibit epimastigote division but does prevent the differentiation of metacyclics. We conclude that epimastigote attachment forms a necessary part of the program of metacyclic development.

Onset of expression of the variant surface glycoproteins of Trypanosoma brucei in the tsetse fly studied using immunoelectron microscopy

The acquisition of the variant surface glycoprotein (variable antigen) coat by metacyclic stage Trypanosoma brucei in the salivary glands of the tsetse fly, Glossina morsitans, has been studied in situ by transmission and scanning electron microscopy using monoclonal antibodies raised against metacyclic variable antigen types and complexed with horseradish peroxidase or colloidal gold. The coat is acquired after binary fission has ceased but while the parasite is still attached to the gland epithelium, i.e. before the mature metacyclic is released into the gland lumen. The variable antigen type heterogeneity previously observed in discharged mature metacyclics is here demonstrated in the nascent (attached) metacyclic population. The variant surface glycoprotein genes are thus not expressed in a fixed sequence since different metacyclic variable antigen types are present ab initio. The distribution of immunogold-marked nascent metacyclics of a particular variable antigen type, as shown by quadrat analysis of a scanning electron micrograph montage of the infected salivary gland epithelium, conforms to a Poisson series. This provides evidence that individual variant surface glycoprotein genes are stochastically activated and suggests that selective activation occurs after trypanosome division has ceased.

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.

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.

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.

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.

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.

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.

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.

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.

Instability of the Trypanosoma brucei rhodesiense metacyclic variable antigen repertoire

Trypanosoma brucei rhodesiense undergoes antigenic variation in its mammalian host by changing the glycoprotein composing its surface coat. Trypanosome clones which have the same repertoire of variable antigen types (VATs) are said to belong to the same serodeme. Tsetse flies infected with a particular serodeme extrude infective metacyclic trypanosomes which express only a restricted part of this repertoire. As the only known acquired immunity in African trypanosomiasis is VAT-specific this limitation of metacyclic VAT (M-VAT) repertoire could be important in devising a vaccine. This possibility of immunoprophylaxis could depend, however, on whether or not the M-VAT repertoire is conserved over long periods of repeated cyclical transmission and between epidemics. Studies reported here on isolates made from an East African focus of sleeping sickness over a 20-yr period suggest substantial changes in the M-VATs expressed during this time. Furthermore, we have detected change in expression of 3 M-VATs during sequential tsetse transmission of a clone in the laboratory indicating a possible instability in the organization of M-VAT genes.

All metacyclic variable antigen types of Trypanosoma congolense identified using monoclonal antibodies

Vaccination against the tsetse-borne trypanosomiases has proved impossible because of the trypanosome's ability to generate a seemingly inexhaustible number of variable antigen types in the blood or tissues of the host. Each variable antigen is a glycoprotein which forms a surface coat on the trypanosome and each glycoprotein is the product of a single gene. The full repertoire of such antigens has not been identified for any trypanosome serodeme (genotype) as yet, but the number of genes coding for variable antigen glycoproteins is estimated to be between 100 and 1,000. We have previously postulated that for Trypanosoma brucei the antigen repertoire of the infective metacyclic stage trypanosomes inoculated by the tsetse fly may be considerably smaller than that expressed in the mammalian host. If this is so then protection against infection by the vector becomes an easier proposition, but the actual scale of the metacyclic repertoire is also unknown. We present here evidence that the metacyclic repertoire of a stock of T. congolense, the most important of the pathogenic cattle trypanosomes, is limited to 12 variable antigen types.

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.

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.

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.

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.

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.

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.

Fusion of host cell secondary lysosomes with the parasitophorous vacuoles of Leishmania mexicana-infected macrophages

Secondary lysosomes of cultured mouse peritoneal macrophages were labeled with the electron-dense colloid saccharated iron oxide; the identity of the labeled structures was checked by the Gomori reaction for acid phosphatase. Amastigotes of Leishmania mexicana mexicana derived from mouse lesions were used to infect these macrophages in vitro. In electron micrographs of thin sections of infected macrophages the labeled secondary lysosomes were seen fused with the parasitophorous vacuoles without preventing subsequent multiplication of the parasites. A similar fusion probably occurs in vivo, and may provide a pathway through which not only nutrients but also drugs and host antibodies could reach the intracellular parasite.