Leishmania major Friedlin chromosome 1 has an unusual distribution of protein-coding genes

Leishmania are evolutionarily ancient protozoans (Kinetoplastidae) and important human pathogens that cause a spectrum of diseases ranging from the asymptomatic to the lethal. The Leishmania genome is relatively small [ approximately 34 megabases (Mb)], lacks substantial repetitive DNA, and is distributed among 36 chromosomes pairs ranging in size from 0.3 Mb to 2.5 Mb, making it a useful candidate for complete genome sequence determination. We report here the nucleotide sequence of the smallest chromosome, chr1. The sequence of chr1 has a 257-kilobase region that is densely packed with 79 protein-coding genes. This region is flanked by telomeric and subtelomeric repetitive elements that vary in number and content among the chr1 homologs, resulting in an approximately 27.5-kilobase size difference. Strikingly, the first 29 genes are all encoded on one DNA strand, whereas the remaining 50 genes are encoded on the opposite strand. Based on the gene density of chr1, we predict a total of approximately 9,800 genes in Leishmania, of which 40% may encode unknown proteins.

Increased expression of LD1 genes transcribed by RNA polymerase I in Leishmania donovani as a result of duplication into the rRNA gene locus

Eukaryotic protein-coding genes are generally transcribed by RNA polymerase II (Pol II), which has a lower transcription rate than that of Pol I. We report here the duplication of two LD1 genes into the rRNA locus and their resultant transcription by Pol I. The multigenic LD1 locus is present in a 2.2-Mb chromosome in all stocks of Leishmania spp. and is also present in multicopy 200- to 450-kb linear chromosomes or multicopy circular DNAs in over 15% of stocks examined. Genomic rearrangement in Leishmania donovani LSB-51.1 resulted in duplication of a 3.9-kb segment of LD1 containing two genes (orfF and orfG) and of a 1.3-kb segment from approximately 10 kb downstream into the rRNA gene repeat region of the 1.2-Mb chromosome. Short sequences (12 or 13 bp) common to the 2.2-Mb LD1 and 1.2-Mb rRNA loci suggest that this gene conversion occurred by homologous recombination. Transcription of the duplicated genes is alpha-amanitin resistant, indicating transcription by Pol I, in contrast to the alpha-amanitin-sensitive (Pol II) transcription of the genes in the 2.2-Mb LD1 locus. This results in higher transcript abundance than expected from the gene copy number in LSB-51.1 and in elevated expression of at least the orfF gene product.

The mucosal and systemic response to phosphorylcholine in mice infected with Trichinella spiralis

The presence of phosphorylcholine (PC) in Trichinella was confirmed by ELISA and Western blot experiments with the PC-specific myeloma TEPC-15. Anti-PC antibody production was detected in ELISA by cross-reaction with the PC-positive somatic polysaccharide of Aspergillus and the synthetic conjugate phosphorylcholine-bovine serum albumin conjugate and by inhibition with phosphorylcholine chloride (PCCl). The kinetics of the serum and mucosal anti-PC immunoglobulin response were determined following infection of CFW mice. Anti-PC IgA was a minor fraction of the serum response. In primary infections IgG binding to Trichinella antigen was partially inhibited by PCCl incubation, but by Day 6 following challenge infections, incubation with PCCl did not reduce IgG binding. PCCl incubation also reduced serum IgM binding to Trichinella antigen following primary infections, and in contrast to IgG, a reduction occurred following challenge infection as well. Following primary and challenge infections PCCl incubations also reduced bile IgA binding to Trichinella antigen. The kinetics and subclass distribution of the anti-Trichinella PC response were equivalent to the group I response reported for synthetic PC-protein conjugates. Anti-PC IgA production indicates that class switching occurred without maturation of the response. Immunization by feeding Trichinella antigen plus cholera toxin, in contrast to infection with larvae, did not affect anti-PC antibody production following infection. Since the response was not anamnestic and the serum IgG response was not downregulated, larval infection and antigen feeding differ in the anti-PC responses they induce. The anti-PC response does not appear to be protective in Trichinella infections in mice.

Trichinella spiralis: the effect of oral immunization and the adjuvancy of cholera toxin on the mucosal and systemic immune response of mice

The effect of oral immunization and the adjuvancy of cholera toxin (CT) were examined in mice infected with Trichinella spiralis. The mean of total muscle larvae was reduced by 36% in mice infected with Trichinella larvae in combination with CT. In mice fed soluble, particulate, or soluble/particulate antigens in combination with CT on Days 0, 14, and 21, and challenged with Trichinella larvae on Day 28, there was a significant reduction in adult worm fecundity (50%), worm size (20-30%), and the mean of total muscle larvae (75%) but no apparent effect on the rate of expulsion on Day 6 postchallenge. Following antigen feeding, but prior to challenge with Trichinella (Day 28), the immunoglobulin response was positive in only a small proportion of mice. On Day 6 following challenge with Trichinella larvae, the biliary immunoglobulin response was enhanced approximately 10-fold (P < 0.05) in all antigen-feeding treatments which included CT, compared with nonimmunized controls or antigen-feeding treatments which did not include CT. Similarly, the serum IgG response was enhanced following challenge with Trichinella larvae in treatments fed soluble, particulate, or soluble/particulate antigens with CT. The response was also enhanced in the particulate, but not in soluble or soluble/particulate antigen treatments without CT.

Characterization of cholinesterases from the parasitic nematode Trichinella spiralis

1. Trichinella cholinesterases occur in multiple molecular forms which differ in size, kinetics, activity with butyrylthiocholine, and effects of inhibitors. 2. The 5.3 and 13S forms identified in Trichinella extracts are also found in C. elegans and other nematodes but the 7S form which occurs in other nematodes was absent from Trichinella detergent extracts. Differences in kinetic and inhibition properties among nematode species were also evident. 3. The level of cholinesterases in excretory/secretory products is low. 4. Trichinella cholinesterases did not elicit a detectable antibody response in mice.

Trichinella spiralis: dose dependence and kinetics of the mucosal immune response in mice

The role of the mucosal immune response in helminth infections is not clear. In this study, the dose dependence and kinetics of the mucosal immune response to Trichinella spiralis were determined in experimentally infected Swiss Webster and BALB/c mice. The primary mucosal isotype was sIgA, although IgG was also detected, and primary infections with 10 and 150 larvae produced an anamnestic response on challenge. The mucosal and systemic immunoglobulin responses were dose dependent in both primary and challenge infections. The fecundity and length of worms and the rate of expulsion from the gut were determined on Day 6 postchallenge in Swiss Webster mice. Adult worm recovery and fecundity were reduced by greater than 50% and worm length by 28% in mice infected and challenged with 10 larvae and by 90, 85, and 35%, respectively, in mice infected and challenged with 150 larvae. The rate of expulsion was correlated with the size of both primary and challenge doses and a reduction in fecundity was correlated with the size of the primary dose only. The reduction in worm length did not differ significantly between the infection doses, but the trend was similar to that for expulsion. In BALB/c mice the expulsion response was dissociated from a reduction in fecundity and worm length, the latter two being positively correlated with sIgA levels, supporting a role for sIgA and/or IgG in these effects. However, expulsion does not appear to be dependent on the mucosal immunoglobulin response.

The use of the polymerase chain reaction to identify porcine isolates of Trichinella

A method was developed to identify domestic isolates of Trichinella using the polymerase chain reaction. Oligonucleotide primers, based on the repetitive DNA sequence (pPRA) from the P1 isolate of Trichinella, were used to amplify genomic DNA from 13 domestic isolates and tested against sylvatic isolates of Trichinella. Pattern differences were observed among domestic isolates, indicating divergence of this repetitive sequence. The primers were specific for domestic Trichinella as no amplification was detected for sylvatic isolates or Trichinella pseudospiralis. It was possible to identify an isolate from a single larva following digestion or in situ in muscle tissue.

A rapid method to determine the isotype and specificity of coproantibodies in mice infected with Trichinella or fed cholera toxin

A method was developed to isolate and test coproantibodies from mice infected with Trichinella or mice fed cholera toxin. It was rapid as results were obtained within 3 h, and it was applicable to a single faecal pellet. It reduced the number of experimental animals required 7-fold, and reduced variability, since samples were obtained from the same experimental animal over time. As it was noninvasive, it did not alter normal gut physiology, nor the course of the parasitic infection. The immune response was monitored over time in individual mice, and specific sIgA and IgG isotypes were detected for both Trichinella and cholera toxin by ELISA.

Identification of two isolates of Trichinella recovered from humans in France

Two Trichinella isolates from humans in France were characterized using reproductive capacity indices and a combination of molecular methods. The isolate TRLL hybridized with the pig type-specific probe pPra and had pig type restriction profiles and rDNA patterns. It was therefore identified as a domestic or pig type isolate. The isolate CTRD-85 had similarities and differences in restriction profiles and rDNA patterns with both AF1 and Trichinella nelsoni and was identified as a sylvatic type. Pattern comparisons also show that T. nelsoni is similar to variants of the North American sylvatic type.

Characterization of the ribosomal DNA from Trichinella spiralis

Ribosomal DNA (rDNA) from three isolates of Trichinella was cloned into phage and sublcloned into the plasmid pBR322. The basic repeat unit of rDNA was variable in size, with the mapped clones ranging from 10-12 kb. There were differences in restriction sites within the genic region among the three isolates which were due to variations in the internal transcribed region (ITS) and the intergenic spacer (IGS). Three RsaI sites were mapped to the IGS repeat unit of the isolate AF1, and one RsaI site was mapped to the IGS repeat unit of Trichinella spiralis pseudospiralis (isolate Tp). The number of repetitive units in the IGS region varied markedly within and between the isolates. It was estimated that the basic repeat unit for the rDNA of isolate P1 was 10.6-28 kb, for AF1 10.7-37 kb, and for Tp it was 11-14.9 kb. There appeared to be a greater frequency of some sizes of the basic repeat unit in each of the populations, based on the relative intensity with which certain bands hybridize to the probe.