Haptoglobin-hemoglobin receptor independent killing of African trypanosomes by human serum and trypanosome lytic factors

The haptoglobin-hemoglobin receptor (HpHbR) of African trypanosomes plays a critical role in human innate immunity against these parasites. Localized to the flagellar pocket of the veterinary pathogen Trypanosoma brucei brucei this receptor binds Trypanosome Lytic Factor-1 (TLF-1), a subclass of human high-density lipoprotein (HDL) facilitating endocytosis, lysosomal trafficking and subsequent killing. Recently, we found that group 1 Trypanosoma brucei gambiense does not express a functional HpHbR. We now show that loss of the TbbHpHbR reduces the susceptibility of T. b. brucei to human serum and TLF-1 by 100- and 10,000-fold, respectively. The relatively high concentrations of human serum and TLF-1 needed to kill trypanosomes lacking the HpHbR indicates that high affinity TbbHpHbR binding enhances the cytotoxicity; however, in the absence of TbbHpHbR, other receptors or fluid phase endocytosis are sufficient to provide some level of susceptibility. Human serum contains a second innate immune factor, TLF-2, that has been suggested to kill trypanosomes independently of the TbbHpHbR. We found that T. b. brucei killing by TLF-2 was reduced in TbbHpHbR-deficient cells but to a lesser extent than TLF-1. This suggests that both TLF-1 and TLF-2 can be taken up via the TbbHpHbR but that alternative pathways exist for the uptake of these toxins. Together the findings reported here extend our previously published studies and suggest that group 1 T. b. gambiense has evolved multiple mechanisms to avoid killing by trypanolytic human serum factors

Genetic analysis of Trypanosoma brucei

Analysis of trypanosomes derived from laboratory crosses showed that minisatellite inheritance is in agreement with a Mendelian system and that such markers are particularly useful for the detection of cross and self-fertilization. Examination of the F1 hybrids from these crosses has identified some hybrids as being trisomic, but that, contrary to previous reports, triploidy is rare. The rate of recombination between homologous chromosomes was also examined and used to estimate the physical distance per centiMorgan (4.9-25kb/cM).Although sexual recombination has been demonstrated to occur in laboratory experiments the extent of genetic exchange in natural populations remained to be elucidated. Analysis of a series of field samples isolated from tsetse flies indicated that a high proportion of tsetse flies harboured mixed T. brucei infections, a prerequisite for genetic exchange to occur in the field.Minisatellite variant repeat PCR (MVR-PCR) was employed, to map the interspersion patterns of variant repeat units within a minisatellite locus, a ternary code for a number of different alleles was generated and from this the underlying mechanism of mutation for one minisatellite (MS42) were inferred. This method of allele mapping was applied to a collection of field samples to study the relationship between T. b. brucei and T. b. rhodesiense populations and the extent of sexual recombination in natural populations in each sub-species. The analysis revealed that there is considerable sub-structuring in T. brucei populations, due to geographical barriers and host specificities. T. b. rhodesiense populations are distinct from T. b. brucei and a T. b. rhodesiense-specific marker has been identified for the Busoga (Uganda) focus

Genetic exchange in <i>Trypanosoma brucei</i>: evidence for mating prior to metacyclic stage development

It is well established that genetic exchange occurs between Trypanosoma brucei parasites when two stocks are used to infect tsetse flies under laboratory conditions and a number of such crosses have been undertaken. Both cross and self-fertilisation can take place and, with the products of mating being the equivalent of F1 progeny in a Mendelian system and. Recently, analysis of a large collection of independent progeny using a series of polymorphic micro and minisatellite markers, has formally demonstrated that the allelic segregation at loci on each of the 11-megabase chromosomes conforms to ratios predicted for a classical diploid genetic system involving meiosis as well as independent assortment of markers on different chromosomes. Further extensive analysis of these F1 progeny, using a large panel of micro and minisatellite markers, has led to the construction of a genetic map of one parasite stock A. MacLeod, A. Tweedie and S. McLellan et al., The genetic map of Trypanosoma brucei, Nucleic Acids Res 33 (2005), pp. 6688–6693. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (10)

Allelic segregation and independent assortment in <i>T. brucei</i> crosses: proof that the genetic system is Mendelian and involves meiosis

The genetic system on Trypanosoma brucei has been analysed by generating large numbers of independent progeny clones from two crosses, one between two cloned isolates of Trypanosoma brucei brucei and one between cloned isolates of T. b. brucei and Trypanosoma brucei gambiense, Type 2. Micro and minisatellite markers (located on each of the 11 megabase housekeeping chromosomes) were identified, that are heterozygous in one or more of the parental strains and the segregation of alleles at each locus was then determined in each of the progeny clones. The results unequivocally show that alleles segregate in the predicted ratios and that alleles at loci on different chromosomes segregate independently. These data provide statistically robust proof that the genetic system is Mendelian and that meiosis occurs. Segregation distortion is observed with the minisatellite locus located on chromosome I of T. b. gambiense Type 2 and neighboring markers, but analysis of markers further along this chromosome did not show distortion leading to the conclusion that this is due to selection acting on one part of this chromosome. The results obtained are discussed in relation to previously proposed models of mating and support the occurrence of meiosis to form haploid gametes that then fuse to form the diploid progeny in a single round of mating

Novel African trypanocidal agents: membrane rigidifying peptides

The bloodstream developmental forms of pathogenic African trypanosomes are uniquely susceptible to killing by small hydrophobic peptides. Trypanocidal activity is conferred by peptide hydrophobicity and charge distribution and results from increased rigidity of the plasma membrane. Structural analysis of lipid-associated peptide suggests a mechanism of phospholipid clamping in which an internal hydrophobic bulge anchors the peptide in the membrane and positively charged moieties at the termini coordinate phosphates of the polar lipid headgroups. This mechanism reveals a necessary phenotype in bloodstream form African trypanosomes, high membrane fluidity, and we suggest that targeting the plasma membrane lipid bilayer as a whole may be a novel strategy for the development of new pharmaceutical agents. Additionally, the peptides we have described may be valuable tools for probing the biosynthetic machinery responsible for the unique composition and characteristics of African trypanosome plasma membranes

Case of Nigeria-Acquired Human African Trypanosomiasis in United Kingdom, 2016.

Human African trypanosomiasis has not been reported in Nigeria since 2012. Nevertheless, limitations of current surveillance programs mean that undetected infections may persist. We report a recent case of stage 2 trypanosomiasis caused by Trypanosoma brucei gambiense acquired in Nigeria and imported into the United Kingdom

Digital gene expression analysis of two life cycle stages of the human-infective parasite, Trypanosoma brucei gambiense reveals differentially expressed clusters of co-regulated genes

&lt;p&gt;&lt;b&gt;Background&lt;/b&gt;&lt;/p&gt; &lt;p&gt;The evolutionarily ancient parasite, Trypanosoma brucei, is unusual in that the majority of its genes are regulated post-transcriptionally, leading to the suggestion that transcript abundance of most genes does not vary significantly between different life cycle stages despite the fact that the parasite undergoes substantial cellular remodelling and metabolic changes throughout its complex life cycle. To investigate this in the clinically relevant sub-species, Trypanosoma brucei gambiense, which is the causative agent of the fatal human disease African sleeping sickness, we have compared the transcriptome of two different life cycle stages, the potentially human-infective bloodstream forms with the non-human-infective procyclic stage using digital gene expression (DGE) analysis.&lt;/p&gt; &lt;p&gt;&lt;b&gt;Results&lt;/b&gt;&lt;/p&gt; &lt;p&gt;Over eleven million unique tags were generated, producing expression data for 7360 genes, covering 81% of the genes in the genome. Compared to microarray analysis of the related T. b. brucei parasite, approximately 10 times more genes with a 2.5-fold change in expression levels were detected. The transcriptome analysis revealed the existence of several differentially expressed gene clusters within the genome, indicating that contiguous genes, presumably from the same polycistronic unit, are co-regulated either at the level of transcription or transcript stability.&lt;/p&gt; &lt;p&gt;&lt;b&gt;Conclusions&lt;/b&gt;&lt;/p&gt; &lt;p&gt;DGE analysis is extremely sensitive for detecting gene expression differences, revealing firstly that a far greater number of genes are stage-regulated than had previously been identified and secondly and more importantly, this analysis has revealed the existence of several differentially expressed clusters of genes present on what appears to be the same polycistronic units, a phenomenon which had not previously been observed in microarray studies. These differentially regulated clusters of genes are in addition to the previously identified RNA polymerase I polycistronic units of variant surface glycoproteins and procyclin expression sites, which encode the major surface proteins of the parasite. This raises a number of questions regarding the function and regulation of the gene clusters that clearly warrant further study.&lt;/p&gt

THE IMPACT OF COVID-19 ON INFORMAL CAREGIVERS IN THE US

Background: Caregiver burden has negative effects on mental and physical health along with quality of life. Meanwhile, social and physical distancing protocols during the COVID-19 pandemic have created additional impacts on informal caregiving in a rapidly changing environment. Early research over the past year suggests that the pandemic has caused increased caregiver burden as well as caregiving intensity among these individuals. Purpose: Our primary purpose in this informational literature review is to describe the impacts of the pandemic on informal caregiver burden and the sudden shift in roles and responsibilities as a result of pandemic-related changes in caregiving. This review will describe emerging effects on various aspects of health among informal caregivers and explore the growing need to support unpaid caregiving during this time. Methods: A streamlined search was conducted to fit the scope of this review, with key terms determined to identify relevant publications. Common research databases and up-to-date mainstream resources were utilized. Notably, we focused on research published or released since March 2020, primarily rapidly reviewed studies, to align with the timing of the COVID-19 pandemic in the US. Results: Early research suggests that the pandemic has worsened caregiver burden and increased caregiving intensity and hours of care among unpaid, informal family caregivers. Reported health impacts include higher stress, pain, and depression, along with decreased social connectedness and quality of life. Notably, however, COVID-related research generally does not focus on the positive aspects of caregiving, such as its role as a source of purpose in life, creating an opportunity to explore ways to boost certain valuable personal resources among caregivers. Conclusions: Informal family caregivers face their own negative health outcomes and distress as a result of greater caregiver burden, intensity, and the changing landscape of caregiving during the ongoing COVID-19 pandemic. Immediate policy and support recommendations should be considered to alleviate informal caregiver burden and provide ongoing resources over the longer term. In addition, future work should explore the potential of boosting positive resources such as resilience and purpose to ease caregiver burden

Human and animal Trypanosomes in Côte d'Ivoire form a single breeding population.

BACKGROUND: Trypanosoma brucei is the causative agent of African Sleeping Sickness in humans and contributes to the related veterinary disease, Nagana. T. brucei is segregated into three subspecies based on host specificity, geography and pathology. T. b. brucei is limited to animals (excluding some primates) throughout sub-Saharan Africa and is non-infective to humans due to trypanolytic factors found in human serum. T. b. gambiense and T. b. rhodesiense are human infective sub-species. T. b. gambiense is the more prevalent human, causing over 97% of human cases. Study of T. b. gambiense is complicated in that there are two distinct groups delineated by genetics and phenotype. The relationships between the two groups and local T. b. brucei are unclear and may have a bearing on the evolution of the human infectivity traits. METHODOLOGY/PRINCIPAL FINDINGS: A collection of sympatric T. brucei isolates from Côte d'Ivoire, consisting of T. b. brucei and both groups of T. b. gambiense have previously been categorized by isoenzymes, RFLPs and Blood Incubation Infectivity Tests. These samples were further characterized using the group 1 specific marker, TgSGP, and seven microsatellites. The relationships between the T. b. brucei and T. b. gambiense isolates were determined using principal components analysis, neighbor-joining phylogenetics, STRUCTURE, FST, Hardy-Weinberg equilibrium and linkage disequilibrium. CONCLUSIONS/SIGNIFICANCE: Group 1 T. b. gambiense form a clonal genetic group, distinct from group 2 and T. b. brucei, whereas group 2 T. b. gambiense are genetically indistinguishable from local T. b. brucei. There is strong evidence for mating within and between group 2 T. b. gambiense and T. b. brucei. We found no evidence to support the hypothesis that group 2 T. b. gambiense are hybrids of group 1 and T. b. brucei, suggesting that human infectivity has evolved independently in groups 1 and 2 T. b. gambiense