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R Hamers

Publications and source records attributed to R Hamers.

At least 55 records · Page 3Linked to original sources
PubMed1991

Chromosome rearrangement in Leishmania mexicana M379.

Circular extrachromosomal elements were observed in a variety of Leishmania species. We show here that two lines originating from the same isolate have been found to contain a circular DNA molecule of 26.6 kb and a linear chromosome of about 250 kb, respectively, which share a homology of more than 20 kb. The circular DNA molecule and its related region on the linear chromosome were cloned and their restriction maps compared. This investigation reveals information about chromosome rearrangement in L. mexicana M379. Further examination will enable us to understand the nature of chromosome rearrangement such as circularization or linearization.

Animals↗
PubMed1991

Evidence for widespread asymptomatic Trypanosoma rhodesiense human infection in the Luangwa Valley (Zambia).

The RoTat 1/2 CATT test developed for Trypanosoma evansi was used in comparison with other diagnostic tests for the detection of T. rhodesiense infection in the northern part of the Luangwa Valley. The human population, the domestic and a large number of game animals were positive with the RoTat 1/2 CATT, the Ag-ELISA, the IFAT and the radioimmunoprecipitation tests. Human sera from these areas precipitated the same trypanosome-antigen components 35S-methionine labelled whereas few differences in band patterns were found between individual game animals. Surprisingly, however, T. rhodesiense could not be isolated from the "Ag-ELISA and radioimmunoprecipitation" positive patients from the Musenga and Kasyasya localities. The fact that the CATT positive humans were positive in antigen detection tests, does indicate that in all probability they carry or had been carrying a subpatent infection. These results suggest that the reservoir for T. rhodesiense in that region is considerable, comprising the game animals and probably to an even greater extent, the human population.

Agglutination Tests↗
PubMed1991

Infectivity of Trypanosoma (Trypanozoon) brucei gambiense for baboons (Papio hamadryas, Papio papio).

In order to study sensitivity or resistance of T.b. gambiense to baboon serum, two species of baboons, P. hamadryas and P. papio were inoculated with T.b. gambiense clone LiTat 1.1. Both species were receptive to infection but, parasitological and immunological parameters showed that P. papio was more trypanotolerant than P. hamadryas. The VAT-specific trypanolysis test and the ELISA, using MoAb for circulating antigen detection may be appropriate for the diagnosis of human trypanosomiasis due to T.b. gambiense.

Animals↗
PubMed1990

Evidence for kinetoplast and nuclear DNA homogeneity in Trypanosoma evansi isolates.

The kinetoplast DNA minicircles from 13 stocks of trypanosomes designated as Trypanosoma evansi were digested with various restriction enzymes. We also examined the distribution of restriction site polymorphisms in the nuclear DNA of 9 of these stocks, using 7 different variable surface glycoprotein (VSG) and non-VSG probes. Restricted kinetoplast DNA (kDNA) fragments of some of these strains were cloned into M13 or PUC 18 vectors and sequenced. The restriction and sequence mapping showed that most of T. evansi isolates belonged to the A1 and A2 types of Borst and to two new closely related types A3 and A4. A notable exception was RoTat 4/1 derived from a Sudanese stock which was found to display a characteristic brucei-like minicircle heterogeneity. The T. evansi minicircles analysed are not only homogeneous in sequence but also the region similar to the conserved region in Trypanosoma brucei and Trypanosoma equiperdum is flanked on its 5' end by a palindromic repeat of part of the conserved region. The highly conserved sequence GGGCGGT which appears to correspond to the initiation of synthesis of one of the Okazaki fragments contains an additional G and is located as in T. brucei and T. equiperdum about 73 bp 5' from the ORI. The nuclear DNA analysis confirms the kDNA study in that all the T. evansi stocks are members of a very homogeneous group in terms of sequence divergence. Moreover, our analysis also confirms that T. evansi is more closely related to the West African T. b. brucei and T. b. gambiense than to other African trypanosomes.

Animals↗
PubMed1990

Molecular cloning and sequence analysis of the gene encoding the major merozoite surface antigen of Plasmodium chabaudi chabaudi IP-PC1.

The complete nucleotide sequence of the gene encoding the precursor to the major merozoite surface antigens of Plasmodium chabaudi chabaudi strain IP-PC1 has been determined. A single open reading frame was detected, that coded for a protein of 199 kDa. The encoded protein (p199) contains putative signal and membrane anchor sequences and shows a clustering of Cys residues in the last 120 amino acids. Incompletely conserved tandem repeat oligopeptides are present at different positions in the molecule. P199 shows 69% overall homology to the analogous antigen in Plasmodium yoelii yoelii strain YM. The divergence between these antigens is largely confined to 4 areas where a number of insertions and/or deletions have occurred. All repeats occur in these divergent regions. The overall homology with both alleles of Plasmodium falciparum PMMSA is 33%.

Amino Acid Sequence↗
PubMed1989

Different mechanisms account for the suppression of interleukin 2 production and the suppression of interleukin 2 receptor expression in Trypanosoma brucei-infected mice.

Lymph node cell populations derived from Trypanosoma brucei-infected mice failed to produce interleukin 2 (IL 2) in response to a potent mitogenic trigger and suppress the potential of normal lymph node cells to secrete IL 2 in co-culture assays. This suppression is promptly restored by the addition of indomethacin, which blocks prostaglandin synthesis, but is not markedly affected by the addition of catalase, which degrades H2O2. The suppression of the IL 2 receptor expression, on the other hand, is not restored by the addition of indomethacin, nor by the simultaneous supply of both indomethacin and catalase. This discrepancy is not caused by an extreme susceptibility of the receptor expression to low prostaglandin (PG) concentrations, but rather by the presence of suppressive cells that operate through a PG-independent mechanism. This suppressive mechanism accounts for the loss of the IL 2 receptors on both the Ly-2+ and the L3T4+ T cell compartment. The indomethacin-treated co-cultures, which manifest a normal IL 2 production but lack the IL 2 receptors, manifest an impaired DNA synthesis and contain a decreased number of T cell blasts.

Animals↗
PubMed1989

Dual role of macrophages in the suppression of interleukin 2 production and interleukin 2 receptor expression in trypanosome-infected mice.

Lymph node cells derived from T. brucei-infected mice fail to produce interleukin 2-(IL2) subsequent to a potent mitogenic trigger and actively suppress the capacity of normal cells to produce IL2 in co-culture experiments. The depletion of Thy-1+ cells does not decrease but rather increases the suppressive potential of the LNC derived from infected mice. A T cell-enriched nylon wool-nonadherent fraction, on the other hand, is not suppressive. The suppression of IL2 production is promptly restored by the addition of prostaglandin synthesis inhibitors suggesting a key role of the prostaglandin-producing macrophages. Our data indicate that such macrophages do not act indirectly through the induction of suppressor T cells, but rather directly interfere with the normal lymph node cells. In contrast to the essential role of prostaglandins in the impairment of IL2 production, these mediators are not involved in the suppression of IL2 receptor expression. Lymph node cells derived from Trypanosoma brucei-infected mice fail to produce interleukin 2 (IL2) subsequent to a potent mitogenic trigger and actively suppress the capacity of normal cells to produce IL2 in co-culture experiments. The depletion of Thy-1+ cells does not decrease but rather increases the suppressive potential of the LNC derived from infected mice. A T cell-enriched nylon wool-nonadherent fraction, on the other hand, is not suppressive. The suppression of IL2 production is promptly restored by the addition of prostaglandin synthesis inhibitors suggesting a key role of the prostaglandin-producing macrophages. Our data indicate that such macrophages do not act indirectly through the induction of suppressor T cells, but rather interfere directly with the normal lymph node cells.

Animals↗
PubMed1989

Identification of virus-like particles in Eimeria stiedae.

When nucleic acid samples purified from sporozoites of Eimeria stiedae were analyzed by agarose gel electrophoresis, an ethidium-stainable band with an apparent electrophoretic mobility of 6.5 kb was consistently observed. The band was readily degradable upon RNAse treatment, and its susceptibility towards ribonuclease A on a decreasing ionic strength was suggestive of double-stranded RNA (dsRNA). Electron microscopy revealed spherical, probably icosahedral, virus-like particles (VLP) with a diameter of 35 nm in sporozoite lysates. The VLP were purified by CsCl buoyant density gradient centrifugation. Upon extraction, these particles yielded dsRNA molecules of a uniform length of 1.63 microns. The presence of the VLP was investigated in different Eimeria strains. All E. stiedae isolates contained the RNA virus, whereas the Eimeria intestinalis and Eimeria magna isolates tested did not. RNA/RNA hybridization experiments where the E. stiedae VLP dsRNA was probed to the genomes of the dsRNA viruses of Trichomonas vaginalis and Giardia intestinalis revealed a strong relatedness of the E. stiedae virus to the G. intestinalis virus, in contrast with the T. vaginalis virus, where no homology could be detected.

Animals↗
PubMed1989

A gene expressed only in serum-resistant variants of Trypanosoma brucei rhodesiense.

The human infective African trypanosomes are host range variants of Trypanosoma brucei which are resistant to a lytic component in primate serum. T. b. rhodesiense occurs both as a form sensitive to lysis by normal human serum and as a form resistant to this lysis. Switching from one phenotype to the other has been observed in both directions. In the cloned T. b. rhodesiense ETAR1-repertoire we have detected 1.5-kb mRNAs only present in the resistant forms. In T. b. gambiense, which always occurs as a normal human serum-resistant form, no such transcript could be detected, indicating that another mechanism of resistance is involved here. Starting from an independent non-cloned T. b. rhodesiense population isolated from an infected patient, both resistant and sensitive trypanosomes have been prepared. Northern blot analysis of the total RNA prepared from these populations has revealed again the differential occurrence of the resistance-specific transcript, indicating that we are dealing with a general phenomenon associated with serum resistance in T. b. rhodesiense. As expected, Southern blot analyses have demonstrated that both serum-resistant and serum-sensitive forms of T. b. rhodesiense contain the gene coding for this transcript.

Amino Acid Sequence↗
PubMed1989

Detection of circulating trypanosomal antigens in Trypanosoma evansi-infected animals using a T. brucei group-specific monoclonal antibody.

An antigen-detection enzyme immunoassay based on a T. brucei group-specific monoclonal antibody was used for the detection of circulating antigens in several animal species experimentally infected with T. evansi stocks from Sudan, Indonesia, Thailand and South America. Circulating antigens were detected as early as 6 days after infection, and they persisted throughout the observation period of up to 60 days postinfection. In an analysis of sera from naturally infected water buffaloes from Thailand, the test identified all the animals with positive parasitological findings, and 3 additional cases that had not been diagnosed by parasitological techniques. In an analysis of sera from pigs on a farm in Thailand suspected of a T. evansi outbreak, the assay detected "antigenaemia" in 66.7% of the animals, with antigen titres ranging from 1:2 to 1.512.

Animals↗
PubMed1989

Modulation of IL-1 production and IL-1 release during experimental trypanosome infections.

Macrophage populations derived from Trypanosoma brucei-infected mice suppress both interleukin-2 (IL-2) production and IL-2 receptor expression. To try to identify the regulatory level by which the T-cell activation is switched off, we have analysed the potential of the suppressive macrophage-like cells to block the secretion of the accessory cell-derived T cell co-stimulator interleukin-1 (IL-1). The IL-1 secretion, however, was found to be greatly increased rather than decreased. The increased secretion was in part caused by an increased release rather than by an increased synthesis. In the presence of an in vitro trigger (lipopolysaccharide), the IL-1 secretion was increased 20-30-fold by the infection whereas the total IL-1 production increased only 1.5-2-fold. Macrophages from infected mice thus manifested a marginally increased IL-1 synthesis but released a markedly larger proportion of the synthesized monokine than normal macrophages. In the absence of an in vitro trigger, the infection caused a 10-15-fold increase in IL-1 synthesis as a consequence of an in vivo preactivation. This increase was only observed when the synthesis of prostaglandins was blocked by addition of indomethacin.

Animals↗
PubMed1988

ELISA assay for melarsoprol.

A sensitive ELISA method has been developed for measuring the trypanocidal drug melarsoprol. The test allows for the detection of the drug in human sera and in cerebrospinal fluid at the ng/ml level. Preliminary analyses on patient sera and CSF confirm the feasibility of the method. Further application of the test will enable to conduct the necessary pharmacokinetic and metabolic studies; the drug monitoring should hopefully result in improved treatment schedules minimizing the undesired side effects, e.g. lethal encephalopathies.

Arsenicals↗
PubMed1987

Experimental Trypanosoma brucei infections selectively suppress both interleukin 2 production and interleukin 2 receptor expression.

Experimental infections with Trypanosoma brucei AnTat 1.1.E not only account for a suppression of interleukin 2 (IL 2) production, but also induce an impairment of IL 2 receptor expression. Indeed, lymph node cells derived from infected mice failed to express IL 2 receptors following mitogenic stimulation as compared to normal controls. This impairment was not attributed to a modulation of the number of T cells and was not caused by the presence of living parasites. Furthermore, the basal level of IL 2 receptor expression could not be re-established through the exogenous supply of recombinant IL 2. This impairment of receptor expression was found to be mediated by suppressive cells that affect the relative number of receptor-positive cells as well as the mean receptor density. On the other hand, the mitogen-induced secretion of other T cell-derived lymphokines was not inhibited during infection, indicating that the severe suppression of IL 2 regulation was not attributed to a total paralysis of the T cell responsiveness.

Animals↗