Early expression of a Trypanosoma brucei VSG gene duplicated from an incomplete basic copy

Synthesis of Galactosylated Glycosylphosphatidylinositol Derivatives from Trypanosoma brucei

Trypanosoma brucei uses variant surface glycoproteins (VSGs) to evade the host immune system and ensure parasitic longevity in animals and humans. VSGs are attached to the cell membrane by complex glycosylphosphatidylinositol anchors (GPI). Distinguishing structural feature of VSG GPIs are multiple α- and β-galactosides attached to the conserved GPI core structure. T. brucei GPIs have been associated with macrophage activation and alleviation of parasitemia during infection, acting as disease onset delaying antigens. Literature reports that link structural modifications in the GPIs to changes in biological activity are contradictory. We have established a synthetic route to prepare structurally overlapping GPI derivatives bearing different T. brucei characteristic structural modifications. The GPI collection will be used to assess the effect of galactosylation and phosphorylation on T. brucei GPI immunomodulatory activity, and to perform an epitope mapping of this complex glycolipid as potential diagnostic marker for Trypanosomiasis. A strategy for the synthesis of a complete α-tetragalactoside using the 2-naphthylmethyl protecting group and for subsequent attachment of GPI fragments to peptides is presented.

Pneumocystis jirovecii--from a commensal to pathogen: clinical and diagnostic review

Pneumocystis pneumonia is an opportunistic disease caused by invasion of unicellular fungus Pneumocystis jirovecii. Initially, it was responsible for majority of morbidity and mortality cases among HIV-infected patients, which later have been reduced due to the introduction of anti-retroviral therapy, as well as anti-Pneumocystis prophylaxis among these patients. Pneumocystis pneumonia, however, is still a significant cause of mortality among HIV-negative patients being under immunosuppression caused by different factors, such as transplant recipients as well as oncologically treated ones. The issue of pneumocystosis among these people is particularly emphasized in the article, since rapid onset and fast progression of severe symptoms result in high mortality rate among these patients, who thereby represent the group of highest risk of developing Pneumocystis pneumonia. In contrast, fungal invasion in immunocompetent people usually leads to asymptomatic colonization, which frequent incidence among healthy infants has even suggested the possibility of its association with sudden unexpected infant death syndrome. In the face of emerging strains with different epidemiological profiles resulting from genetic diversity, including drug-resistant genotypes, the colonization phenomenon desires particular attention, discussed in this article. We also summarize specific and sensitive methods, required for detection of Pneumocystis invasion and for distinguish colonization from the disease.

Mosaic VSGs and the scale of Trypanosoma brucei antigenic variation

A main determinant of prolonged Trypanosoma brucei infection and transmission and success of the parasite is the interplay between host acquired immunity and antigenic variation of the parasite variant surface glycoprotein (VSG) coat. About 0.1% of trypanosome divisions produce a switch to a different VSG through differential expression of an archive of hundreds of silent VSG genes and pseudogenes, but the patterns and extent of the trypanosome diversity phenotype, particularly in chronic infection, are unclear. We applied longitudinal VSG cDNA sequencing to estimate variant richness and test whether pseudogenes contribute to antigenic variation. We show that individual growth peaks can contain at least 15 distinct variants, are estimated computationally to comprise many more, and that antigenically distinct 'mosaic' VSGs arise from segmental gene conversion between donor VSG genes or pseudogenes. The potential for trypanosome antigenic variation is probably much greater than VSG archive size; mosaic VSGs are core to antigenic variation and chronic infection.

Gene conversion is a convergent strategy for pathogen antigenic variation

Recent studies on three unrelated vector-borne pathogens, Anaplasma marginale, Borrelia hermsii and Trypanosoma brucei, illustrate the central importance of gene conversion as a mechanism for antigenic variation, which results in subsequent evasion of the immune response and persistence in the reservoir host. The combination of genome sequence data and in vivo studies tracking variant emergence not only provides insight into the genetic mechanisms for variant generation and hierarchy in variant expression but also highlights gaps in our knowledge regarding variant capacity and usage in vivo.

Pneumocystis oryctolagisp. nov., an uncultured fungus causing pneumonia in rabbits at weaning: review of current knowledge, and description of a new taxon on genotypic, phylogenetic and phenotypic bases

The genus Pneumocystis comprises noncultivable, highly diversified fungal pathogens dwelling in the lungs of mammals. The genus includes numerous host-species-specific species that are able to induce severe pneumonitis, especially in severely immunocompromised hosts. Pneumocystis organisms attach specifically to type-1 epithelial alveolar cells, showing a high level of subtle and efficient adaptation to the alveolar microenvironment. Pneumocystis species show little difference at the light microscopy level but DNA sequences of Pneumocystis from humans, other primates, rodents, rabbits, insectivores and other mammals present a host-species-related marked divergence. Consistently, selective infectivity could be proven by cross-infection experiments. Furthermore, phylogeny among primate Pneumocystis species was correlated with the phylogeny of their hosts. This observation suggested that cophylogeny could explain both the current distribution of pathogens in their hosts and the speciation. Thus, molecular, ultrastructural and biological differences among organisms from different mammals strengthen the view of multiple species existing within the genus Pneumocystis. The following species were subsequently described: Pneumocystis jirovecii in humans, Pneumocystis carinii and Pneumocystis wakefieldiae in rats, and Pneumocystis murina in mice. The present work focuses on Pneumocystis oryctolagi sp. nov. from Old-World rabbits. This new species has been described on the basis of both biological and phylogenetic species concepts.

Epitope mapping of a protective monoclonal antibody against Pneumocystis carinii with shared reactivity to Streptococcus pneumoniae surface antigen PspA

Pneumocystis carinii is an opportunistic fungal pathogen that causes pneumonia in the immunocompromised host. A protective monoclonal antibody (MAb) termed 4F11 generated against mouse-derived P. carinii was shown by indirect immunofluorescence assay (IFA) to bind surface antigens of P. carinii derived from multiple host species, including humans. We have identified multiple epitopes recognized by MAb 4F11 in two recombinant mouse P. carinii antigens. The epitopes mapped have similar proline content and positive charge distribution. The consensus 8-mer epitope recognized by MAb 4F11 is K/RPA/RPK/QPA/TP. Immune sera raised against intact mouse P. carinii recognized native antigens affinity purified with MAb 4F11 and a recombinant antigen reactive with MAb 4F11. Database searches for short, nearly exact matches to the mapped MAb 4F11 epitopes identified a bacterial surface antigen, Streptococcus pneumoniae PspA, with a similar proline-rich region. In an IFA, MAb 4F11 detected antigens on the S. pneumoniae surface, and Western blotting identified a protein in S. pneumoniae lysates consistent with the M(r) of PspA. A fragment of the S. pneumoniae PspA gene was cloned and sequenced, and the deduced amino acid sequence contained a region with strong similarity to the MAb 4F11 epitopes identified in P. carinii. The PspA recombinant polypeptide was recognized by MAb 4F11 in a Western blot. The ability of MAb 4F11 to recognize similar proline-rich epitopes may explain its ability to recognize P. carinii derived from multiple hosts and will permit testing of the epitopes recognized by this antibody in immunization against P. carinii.

A new name (Pneumocystis jiroveci) for Pneumocystis from humans

The disease known as Pneumocystis carinii pneumonia (PCP) is a major cause of illness and death in persons with impaired immune systems. While the genus Pneumocystis has been known to science for nearly a century, understanding of its members remained rudimentary until DNA analysis showed its extensive diversity. Pneumocystis organisms from different host species have very different DNA sequences, indicating multiple species. In recognition of its genetic and functional distinctness, the organism that causes human PCP is now named Pneumocystis jiroveci Frenkel 1999. Changing the organism's name does not preclude the use of the acronym PCP because it can be read "Pneumocystis pneumonia." DNA sequence variation exists among samples of P. jiroveci, a feature that allows reexamination of the relationships between host and pathogen. Instead of lifelong latency, transient colonization may be the rule.

Pneumocystis carinii f. sp. hominis is not infectious for SCID mice

The infectious power of Pneumocystis carinii f. sp. hominis was explored by inoculating SCID mice intranasally with either P. carinii f. sp. hominis or P. carinii f. sp. muris isolates. Only mice inoculated with mouse parasites developed Pneumocystis pneumonia, as assessed by microscopy and PCR. These results suggest that humans do not contract pneumocystosis from animals.

Genetic divergence at the SODA locus of six different formae speciales of Pneumocystis carinii

Genetic divergence at the SODA (manganese-dependent superoxide dismutase, MnSOD) locus were compared in six Pneumocystis carinii formae speciales isolated from mouse, rabbit, human, macaque and pig. A degenerate oligonucleotide primer strategy was designed to amplify 85-90% of the full-length SODA gene from P. carinii genomic DNA isolates. DNA sequence analysis revealed an A/T bias in the nucleotide composition (71-77.2%) and the presence of seven small introns (41-142 bp), interrupting each P. carinii open reading frame (ORF) at the same position. The MnSOD deduced amino acid sequences from all P. carinii isolates shared residues which were conserved within the MnSOD family and which are required for enzymatic activity and binding of the cofactor metal. Phylogenetic analysis including MnSOD sequences from representatives of the fungal phyla Basidiomycota and Ascomycota indicated that the P. carinii formae speciales form a monophyletic group that is related to the budding yeasts (subphylum Saccharomycotina, previously called class Hemiascomycetes) in the Ascomycota. In the whole Pneumocystis group, P. carinii f. sp. hominis, P. carinii f. sp. macacae and P. carinii f. sp. oryctolagi MnSOD sequences clustered together, as did the rat-derived P. carinii and P. carinii f. sp. muris sequences.

Ultrastructural and molecular characterization of Pneumocystis carinii isolated from a rhesus monkey (Macaca mulatta)

High levels of heterogeneity have been observed among isolates of Pneumocystis carinii derived from different mammalian host species. We report the characterization of P. carinii isolated from a rhesus monkey (Macaca mulatta), which was immunosuppressed as a result of infection with a chimeric simian-human immunodeficiency virus (SHIVsbg). Histopathological examination showed evidence of severe P. carinii pneumonia with a large predominance of trophozoite forms. Alveolitis consisted of typical foamy, honeycomb exudate, with only a few alveolar macrophages. The lung inflammatory response was rather moderate without type-2 pneumocyte hyperplasia or collagenosis. P. carinii organisms were sometimes observed in the bronchiolar lumen. Ultrastructurally, macaque-derived P. carinii was more similar to human- or rabbit-derived parasites than to mouse-derived P. carinii. Molecular studies were carried out on the macaque-derived P. carinii DNA at two genetic loci: the genes encoding the mitochondrial large subunit ribosomal RNA (mt LSU rRNA) and the mitochondrial small subunit ribosomal RNA (mt SSU rRNA). Comparison of the DNA sequences with those from P. carinii isolated from eight other host species demonstrated that the macaque-derived P. carinii was genetically distinct at both loci, and was more closely related to human-derived P. carinii than to P. carinii derived from non-primate sources. We propose that macaque-derived P. carinii be named Pneumocystis carinii f.sp. macacae.

Analysis of a variant surface glycoprotein gene expression site promoter of Trypanosoma brucei by remodelling the promoter region

Trypanosoma brucei survives in the mammalian bloodstream by antigenic variation of its variant surface glycoprotein (VSG) coat. VSG genes are found in telomeric expression sites (ESs), and only one ES is fully transcribed at a time. The parasite changes its coat by either bringing another VSG gene into the active ES, or by switching on another ES and silencing the first. It has previously been shown that the promoter of an active ES can be replaced by a ribosomal promoter without affecting the function of the ES. This study has now analysed the conserved sequences flanking the ES promoter by deletion or replacement of these sequences in intact trypanosomes. The results show that the sequences 3' of the promoter and extending down to the first protein-coding gene, ESAG 7, are not required in the bloodstream-form parasite either for high-level transcription or for switching of the ES. Transformants in which the sequences 5' of the promoter extending up to simple-sequence 50-bp repeats had been removed were not obtained unless the 5' ES sequences were replaced with exogenous DNA, or unless the ES promoter was replaced by a ribosomal promoter, and even these transformants were rare. Transformants lacking the 5' ES sequences displayed a less complete transcriptional repression of silent ESs. These results indicate that the area 5' of an ES promoter is required for optimal functioning of an ES.

Sequence divergence in a family of variant surface glycoprotein genes from trypanosomes: coding region hypervariability and downstream recombinogenic repeats

The surface of the parasitic protozoan Trypanosoma brucei spp. is covered with a dense coat consisting of a single type of glycoprotein molecule, the variant surface glycoprotein (VSG). There may be as many as 1,000 genes for VSG within the genome of T. brucei, and the switch of expression from one to another is the phenomenon of antigenic variation. As an approach to understanding the evolution of VSG genes we have determined the genomic DNA sequences of the eight genes encoding the variant surface glycoprotein 117 (VSG) family. From these data we have observed a number of features concerning the relationships between these genes: (1) there is a region of high variability confined to the N-terminus of the coding sequence, and comparison of the sequences with the available X-ray diffraction crystal structures suggests that two of the most variable stretches within the N-terminal domain are present on surface-exposed loops, indicating a role for epitope selection in evolution of these genes; (2) the 29 nucleotides surrounding the splice acceptor site are absolutely conserved in all eight 117 VSG genes; (3) numerous insertion/deletion mutations are located within or immediately downstream of the C-terminal protein-coding sequences: (4) within 500 bp downstream of the insertion/deletion mutations are one or two copies of a repeat motif highly homologous to the recombinogenic 76-bp repeat sequences present upstream of many VSG basic copy genes and the expression-linked copy.

Targeting of exogenous DNA into Trypanosoma brucei requires a high degree of homology between donor and target DNA

Integration of exogenous DNA into the trypanosome genome occurs by homologous recombination only. To test whether a high degree of homology between donor and target DNA is required, we have inserted marker genes for drug resistance into the promoter area of variant surface glycoprotein (VSG) gene expression sites of Trypanosoma brucei, using targeting fragments from two expression sites that are 92% identical. We observed integrations into expression sites that are known to be perfectly matched to the donor flanks, and into subsets of uncharacterized expression sites that are specific for each type of targeting fragment, and that could be similar or identical to the donor flanks. This requirement for very high homology was found in both procyclic and bloodstream-form trypanosomes. We speculate that trypanosomes have a mismatch repair system that suppresses recombination between divergent DNA sequences, and we discuss ways in which the trypanosome might circumvent the requirement for perfect DNA homology in the duplicative transposition of a VSG gene into a VSG gene expression site.