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R Hamers

Publications and source records attributed to R Hamers.

At least 37 records · Page 2Linked to original sources
PubMed1994

[Evaluation of a direct serologic card agglutination test for the diagnosis of camel trypanosomiasis caused by Trypanosoma evansi].

The results of a novel direct serological card agglutination test for the diagnosis of camel trypanosomosis due to Trypanosoma evansi (CATT/T. evansi) were compared with those obtained by direct detection of parasites in a study using 1,093 sera from camels raised in northern Mali. A good correlation was revealed between the percentage of positive results obtained by CATT and the presence of trypanosomes (89%), as well as a good coincidence between the percentage of positive results obtained by CATT and low haematocrit values (packed cell volume). CATT revealed a global serological prevalence of 30.6%, whereas trypanosomes were found in only 5.85% of the corresponding animals. CATT/T. evansi is a quick and easy-to-read test, which merits further evaluation in camel-rearing countries.

Age Factors↗
PubMed1993

Naturally occurring antibodies devoid of light chains.

Random association of VL and VH repertoires contributes considerably to antibody diversity. The diversity and the affinity are then increased by hypermutation in B cells located in germinal centres. Except in the case of 'heavy chain' disease, naturally occurring heavy-chain antibodies have not been described, although antigen binding has been demonstrated for separated heavy chains or cloned VH domains. Here we investigate the presence of considerable amounts of IgG-like material of M(r) 100K in the serum of the camel (Camelus dromedarius). These molecules are composed of heavy-chain dimers and are devoid of light chains, but nevertheless have an extensive antigen-binding repertoire, a finding that calls into question the role of light chains in the camel. Camel heavy-chain IgGs lack CH1, which in one IgG class might be structurally replaced by an extended hinge. Heavy-chain IgGs are a feature of all camelids. These findings open new perspectives in the engineering of antibodies.

Amino Acid Sequence↗
PubMed1993

Polymerase chain reaction-mediated cloning and in vitro translation of the genes coding for the structural proteins of hog cholera virus.

After amplification by PCR, the 5' region of the genome of hog cholera virus (HCV) strain Alfort 187 was cloned and sequenced. The nucleotide and deduced amino acid sequences were compared with the ones of other pestiviruses. By in vitro translation experiments we were able to demonstrate the protease activity of the p 20 protein of HCV.

Base Sequence↗
PubMed1993

Characterization of structural and non-structural proteins of hog cholera virus by means of monoclonal antibodies.

A panel of 15 monoclonal antibodies, produced against the hog cholera virus, were characterized by radioimmunoprecipitation assays. Using this panel, we were able to identify 4 sets of monoclonal antibodies precipitating each a different viral protein with relative molecular weight of 40, 46, 120 kDa, respectively, and a protein complex containing 15, 16, 27, and 55 kDa polypeptides which were further characterized. One monoclonal antibody recognized an antigenic determinant at the C-terminal cleavage product of the non-structural p 125 of BVDV. The 40 kDa protein was precipitated from the pelleted virions, indicating its structural importance. On the contrary the 46 kDa protein could only be precipitated from the cell lysate and not from the pelleted virions. The glycosylated 15/16 kDa-55 kDa proteins form a disulfide linked heterodimer on the virus particle with a relative molecular weight of 65 kDa.

Animals↗
PubMed1993

IMOL 881, a new trypanocidal compound.

A new drug molecule (IMOL 881) was synthesized and is showing interesting trypanocidal properties. The test results on animal models indicate activity against several trypanosome species, both in the veterinary and in the human medicine application fields. The species tested so far include: T. evansi, T. equiperdum, T. gambiense and T. rhodesiense. The good activity combined with a relatively low toxicity results in a high therapeutic index (> 100). In addition to its curative properties, the drug also seems to exhibit a prophylactic potential, as evidenced by tests on drug treated mice, subsequently infected with T. evansi.

Animals↗
PubMed1993

Murine tumour necrosis factor plays a protective role during the initial phase of the experimental infection with Trypanosoma brucei brucei.

Soluble extracts from salivarian trypanosomes (Trypanosoma brucei brucei, T. evansi and T. congolense) were shown to be capable of inducing murine tumour necrosis factor (mTNF) secretion, both in vivo and in vitro, whereas the soluble extract of an intracellular trypanosome (T. cruzi) failed to do so. Furthermore, the role of mTNF during the initial phase of experimental infections with T. brucei was studied by treating infected mice with mTNF-inducing trypanosoma soluble extract and with neutralizing monoclonal anti-mTNF antibodies. Treatment of the infected animals with different doses of T. brucei soluble extract resulted in a lower first parasitaemia peak (low lysate dose) and in a longer survival time or in a nearly total inhibition of parasite development (high lysate dose). Cotreatment of the infected mice with both anti-mTNF antibodies and a high dose of soluble extract completely restored the parasite development in both trypanosusceptible C3H/He mice and trypanosubtolerant CBA Ca mice, indicating a protective role of mTNF during the parasitaemia. Collectively these results suggest a negative influence of mTNF on T. brucei development in vivo.

Animals↗
PubMed1993

Phosphorylation of infected erythrocyte membrane proteins in Plasmodium chabaudi.

We identify phosphoproteins that are associated to the infected erythrocyte membrane of Plasmodium chabaudi. The specific antibodies that recognize the erythrocyte membrane-associated antigens, namely PcEMA1 and PcLEMA, are studied. According to sequencing analysis, neither the gene structure nor the predicted properties of these two antigens are completely distinct. The PcEMA1 is a 50 kDa acidic protein, with a pI of about 4.4, that contains 25 phosphorylation sites principally located in the repetitive sequence. Almost all of this molecule is hydrophilic. The predicted (predictment ability) of this protein is, hence, associated to the host's erythrocyte cytoskeleton and it is synthesized through an entire erythrocyte cycle. PcLEMA, instead, is a 74 kDa basic protein, with a pI of about 9.8, that contains 11 possible phosphorylation sites. This gene contains two exons: exon 1 shows transmembrane characteristics while exon 2 contains part of the hydrophilic repetitive sequences. Thus this protein is predicted as a transmembrane-associated protein and is synthesized only at the last stages of the erythrocytic cycle. In in-vitro phosphorylation experiments, both PcEMA1 and PcLEMA are phosphorylated by endogenous kinases activities. However, the degree of phosphorylation differs between the two in that PcEMA1 reveals a higher phosphorylation intensity than PcLEMA.

Animals↗
PubMed1993

Karyotype polymorphism and conserved characters in the Leishmania (Viannia) braziliensis complex explored with chromosome-derived probes.

Molecular karyotype of 45 reference populations of Neotropical leishmanias was analyzed with ethidium bromide staining and with 6 chromosome-derived probes selected from a genomic library of Leishmania (Viannia) braziliensis. Size-conserved patterns were identified and found to be specific to subgenus Viannia and to its constitutive species. An important issue for epidemiology and clinical investigations was the discrimination between L. (V.) peruviana and L. (V.) braziliensis, 2 species found very similar by other genetic techniques, but responsible for totally different clinical patterns. The suggested existence of genetically distinct demes, or karyodemes, within the group-species might also show to be of importance, as these populations might differ in virulence, host-specificity and clinical manifestations.

Animals↗
PubMed1992

Dynamics and size polymorphisms of minichromosomes in Leishmania major LV-561 cloned lines.

Various lines and cloned lines of Leishmania major of varying degrees of virulence in BALB/c mice possessed size polymorphic multicopy minichromosomes related to previously described LD1/CD1 and 715-class DNAs of Leishmania. The minichromosomes were not necessary for virulence. Two of these DNAs (M180 and M210), coexisting in a single cloned line, showed remarkable dynamics in terms of loss or gain when followed through multiple transfers during in vitro culture and in vivo passage in BALB/c mice. Although there was significant sequence heterogeneity among minichromosomes, M180 sequences were present within large (megabase) and in intermediate (550-760 kb) chromosomes in the L. major lines analysed. M180 related small DNAs were also detected in Leishmania mexicana and Leishmania donovani isolates, suggesting that the generation of these molecules involves a common, probably functional basic mechanism widespread in Leishmania.

Animals↗
PubMed1992

Structure of a Plasmodium chabaudi acidic phosphoprotein that is associated with the host erythrocyte membrane.

We have characterized by molecular cloning and sequencing a Plasmodium chabaudi antigen that is associated with the membrane of the infected erythrocyte throughout the entire intraerythrocytic cycle. The protein (PcEMA1) has a predicted size of 50 kDa and contains a major tandem repeat array of 16 octapeptides that constitutes almost 30% of the protein. At its amino-terminus, PcEMA1 has a string of hydrophobic residues characteristic of a secreted protein, but does not contain a hydrophobic membrane-spanning segment. The antigen appears to reside on the cytoplasmic face of the erythrocytic membrane. PcEMA1 has a predicted pI of 4.4 and is a potential phosphoprotein.

Amino Acid Sequence↗
PubMed1992

Only the serum-resistant bloodstream forms of Trypanosoma brucei rhodesiense express the serum resistance associated (SRA) protein.

The Trypanosoma brucei species consists of three subspecies. T. b. rhodesiense and T. b. gambiense are human infective forms, while T. b. brucei is lysed upon exposure to the cytotoxic factor in normal human serum. T. b. rhodesiense can however occur as a serum-resistant (R) and as a serum-sensitive form (S). In a study of the molecular basis of serum resistance in T. b. rhodesiense it was shown that in the cloned ETaR1-repertoire only the serum-resistant variants express specific transcripts, encoding a protein with VSG-characteristics. When a serial of freshly isolated T. b. rhodesiense isolates was tested, the presence of the R-transcripts in the serum-resistant populations was confirmed. The absence of the serum resistance associated (SRA) mRNAs in several isolates from T. b. brucei and especially T. b. gambiense (including an a-typical one), indicates that more than one mechanism might be involved in the phenomenon of serum resistance in the T. brucei group. Neither T. evansi, nor T. equiperdum expresses the SRA-transcripts. Interestingly, the transcription of the R-specific transcripts is not maintained during the life cycle of T. b. rhodesiense; in the procyclic forms the SRA-mRNAs are no longer present.

Animals↗
PubMed1992

Mechanisms underlying trypanosome-elicited immunosuppression.

T-cell proliferative responses of lymph node cells are profoundly suppressed during experimental infections of mice with Trypanosoma brucei. The active suppression of lymph node T-cell proliferative responses is attributed to the coexistence of at least two unlinked suppressive mechanisms that block different T-cell regulatory steps and operate through different effector mechanisms. The generation of prostaglandin-producing macrophages is entirely responsible for the suppression of IL-2 production whereas the induction of a prostaglandin-independent suppressive mechanism accounts for the suppression of the expression of IL-2 receptors (IL-2R). Both mechanisms are mediated by the cells that co-purify which macrophages. Despite an impairment at the level of T-cell proliferation, lymph node cells from T. brucei infected animals produce substantial amounts of interferon-gamma (IFN-gamma) and this lymphokine participates in the down-regulation of IL-2R expression. T-brucei-pulsed macrophage cell lines acquire concomitantly the potential to suppress T-cell proliferative responses and to stimulate CD8+ T-cells to secrete IFN-gamma. The sensibilization of CD8+ T cells by T. brucei-pulsed macrophages might be mediated by TNF-alpha. Collectively, these results indicate that the uptake of T. brucei by macrophages, either in vivo or in vitro, results in the generation of suppressive cells that annihilate T-cell proliferative responses. Furthermore, at least two cytokines (i.e., TNF-alpha and IFN-gamma) are released during these interactions. Besides playing a role in the pathway of T-cell immunosuppression, TNF-alpha and IFN-gamma could also contribute to immunopathological features that occur during trypanosome infections.

Animals↗
PubMed1991

In vitro study on the impact of fish sera on the survival and fine structure of the eel-pathogenic acanthocephalan Paratenuisentis ambiguus.

The effects of fish sera on the growth and fine structure of infective larvae of the eel-pathogenic acanthocephalan Paratenuisentis ambiguus (Eoacanthocephala: Tenuisentidae) were studied under in vitro conditions using sera from the final host Anguilla anguilla and from two accidental fish hosts as well as fetal calf serum. As controls larvae were also kept in medium in the absence of serum and in experimentally infected eels. Sera from the accidental fish hosts carp and rainbow trout exerted toxic effects on the acanthocephalans. Worms maintained in medium containing sera from these two fish were contracted and displayed inverted probosces. Moreover, the tegument exhibited vacuolization and the formation of necrotic areas, including lysis of the mitochondria. Due to these effects, the parasites died at 21 (rainbow trout) or 21-50 days (carp) post-incubation. Eel sera had no toxic effect on the infective larvae. The growth of the larvae in medium depended on the composition of the latter, but was reduced as compared with that in the natural final host. Based on these results, we conclude that components of the hosts' blood sera play a role in the determination of the host specificity of P. ambiguus.

Acanthocephala↗