Biomedical subjects

G Mayrhofer

Publications and source records attributed to G Mayrhofer.

At least 55 records · Page 3Linked to original sources

PubMed1992

Selection of specific genotypes of Giardia intestinalis by growth in vitro and in vivo.

This study examined whether allelic changes observed when clinical isolates of Giardia intestinalis made in suckling mice were adapted to in vitro growth occurred as a result of gene switching (alternate isoenzymes) or through selection of organisms with different genotypes from mixed infections. Samples were compared electrophoretically at 20 enzyme loci. Marked allelic differences were detected between the uncloned clinical isolates grown in mice and the axenic cultures established from them. Furthermore, the allelic profiles of the uncloned isolates changed during the course of in vivo or in vitro growth. In contrast, all clones produced from each isolate retained identical allelic profiles, regardless of whether they were grown in vivo or in vitro. These findings argue against gene switching as an explanation for the observed allozyme changes and support preferential selection of organisms with specific genotypes by growth conditions. The data indicate the presence of at least 2 and possibly up to 4 distinct genotypes within each clinical isolate. The genetic differences detected between clinical isolates in suckling mice were of similar magnitude to those that separate different axenic isolates of G. intestinalis into cryptic species. Conversely, the genetic differences between the isolates were limited when sampled after establishment in vitro. These findings have significant implications for research on Giardia and other medically important parasites and raise the possibility that culture may exert a similar selective bias on the genotypes isolated from infections with other parasitic protozoa.

Alleles↗

PubMed1992

Uterine epithelial cells synthesize granulocyte-macrophage colony-stimulating factor and interleukin-6 in pregnant and nonpregnant mice.

Cytokine secretion by endometrial cells from estrous and mated mice was measured using specific bioassays. The granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-6 (IL-6) contents of uterine intraluminal fluid were elevated greater than 20-fold and 250-fold respectively following mating, and both cytokines were synthesized in abundance in vitro by uterine cells harvested at estrus and on Day 1 of pregnancy. Synthesis was not impaired in genetically lymphocyte-deficient nude, SCID, or beige mice. To determine the cellular origin of the cytokines, a panning technique employing monoclonal antibodies against a range of leukocyte and other lineage markers was used to isolate uterine cell subsets in vitro. These experiments identified glandular and/or luminal epithelial cells as the major source of GM-CSF and IL-6 in estrous and pregnant uteri. Stromal fibroblasts also synthesized IL-6, as did macrophages in mated mice. Epithelial cells harvested from midgestation uteri secreted GM-CSF and IL-6 in quantities similar to those of cells from estrous and mated mice. Bioactivities of both cytokines derived from epithelial cells were neutralized by specific antibodies, and size-exclusion chromatography of conditioned media from uterine cells revealed peaks of GM-CSF and IL-6 bioactivity with M(r) 23,000 and 23,000-26,000, respectively. Bioassay of luminal fluids and culture supernatants were negative for the cytokines interleukin-1, interleukin-2, interleukin-3, and tumor necrosis factor-alpha. These studies identify murine uterine epithelium as a potent source of the cytokines GM-CSF and IL-6, which we postulate have potentially important functions in pregnancy through actions on target cells in both the uterus and the conceptus.

Animals↗

PubMed1992

Distinct genetic groups of Giardia intestinalis distinguished by restriction fragment length polymorphisms.

The taxonomic status of the parasitic protozoal species Giardia intestinalis depends on the morphological similarity of all Giardia isolated from humans and the presumption that Giardia are host-specific. On the basis of electrophoretic data derived from examination of 26 enzyme loci in Australian isolates, it has been proposed that G. intestinalis is a species complex comprising three or four genetically distinct (but morphologically cryptic) species. These received the tentative designations of genetic groups I-IV (R. H. Andrews, M. Adams, P. F. L. Boreham, G. Mayrhofer & B. P. Meloni. International Journal for Parasitology 19, 183-190, 1989). In the present study, two unrelated DNA probes (one specific for a gene encoding a trophozoite surface protein, the other detecting a non-coding repetitive sequence within the G. intestinalis genome) were used in Southern hybridization analyses to examine 10 axenic isolates of G. intestinalis, established from diverse geographical regions in Australia, together with the Portland-1 isolate from the USA. Both probes identified every isolate unambiguously as belonging to one or other of two genetic clusters. Electrophoretic analysis of the same samples indicated that these clusters correspond to the previously defined genetic groups I and II. No heterogeneity was apparent within the seven group I isolates using either probe. However, when probed with the repetitive sequence, the four isolates belonging to group II exhibited small differences in banding patterns, suggesting that this group may be less homogeneous than group I.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Prevention of chronic erosive streptococcal cell wall-induced arthritis in rats by treatment with a monoclonal antibody against the T cell antigen receptor alpha beta.

Rats treated with an mAb (R73) against the TCR-alpha beta failed to develop chronic persistent arthritis after injection of streptococcal cell walls. Histologically, R73 mAb-treated rats had mild hyperplasia of synovial lining cells and minimal destruction of cartilage. In contrast, control-treated animals developed marked pannus formation, with pronounced infiltration of mononuclear cells and severe destruction of cartilage and subchondral bone. The preventive effect of R73 mAb on streptococcal cell wall-induced arthritis was associated with the marked depletion of alpha beta + T cells by R73 mAb. These results indicate that T cells play a crucial role in chronic erosive streptococcal cell wall-induced arthritis.

Animals↗

PubMed1991

Treatment of collagen-induced arthritis in rats with a monoclonal antibody against the alpha/beta T cell antigen receptor.

A monoclonal antibody (MAb) to the alpha/beta T cell receptor (TCR alpha/beta), R73 MAb, completely blocked the induction of collagen-induced arthritis (CIA) in rats when the MAb was administered at the time of immunization with type II collagen. When administered after CIA had begun, the progression of the arthritis was suppressed significantly by R73 MAb treatment. The preventive and suppressive effects of R73 MAb on CIA were associated with the depletion of peripheral blood alpha/beta-positive T cells. These results indicate that alpha/beta-positive T cells play a role in the progression of existing CIA as well as in its induction.

Animals↗

PubMed1991

Characteristics of thymidine transport in Giardia intestinalis trophozoites.

The transport of thymidine by the protozoan parasite Giardia intestinalis was examined at 0 degrees C. This temperature prevented attachment of the cells to vessel walls, so that a rapid sampling technique could be used. Thymidine influx (distinguished from gross uptake) was readily measurable at 0 degrees C and was specific and saturable. The transporter appears to be a facilitative carrier, exhibiting a high affinity for thymidine (Km = 50 microM). Thymine and uracil were the most effective inhibitors (Ki = 30 microM and 45 microM, respectively), followed by thymidine, deoxyuridine and uridine (Ki = 64-96 microM). Cytosine, cytidine and deoxycytidine were not inhibitory, even at high concentrations. The data indicate that the oxygen at position 4 of the pyrimidine ring is essential for recognition by the transporter, whereas the 5-methyl group of thymine is unimportant. The furanose ring appears not to be recognized, since D-ribose was non-inhibitory and uridine and deoxyuridine were equally inhibitory but less so than uracil and thymine. This carrier probably mediates the transport of uracil, as well as uridine and thymidine, although influx of the base remains to be measured.

Animals↗

PubMed1991

Amino-terminal domain of the El Tor haemolysin of Vibrio cholerae O1 is expressed in classical strains and is cytotoxic.

Previous studies have shown that the classical isolates of Vibrio cholerae possess an 11 bp deletion in the structural gene for the El Tor haemolysin leading to the production of a 27 kDa non-haemolytic truncated product HlyA* compared to the 82 kDa haemolysin, HlyA. These studies were designed to assess whether this truncated product had any biological activity. A KmR cartridge was introduced into the hlyA gene effectively eliminating the haemolysin. This was recombined into the chromosome of a variety of strains and isogenic pairs were examined in a number of systems. These studies suggest that the haemolytic (cytolytic) domain of HlyA resides at the C-terminus and that the N-terminus, which is conserved as HlyA* in classical strains, possesses enterotoxic (cytotoxic) activity. Experiments with the cholera-toxinless vaccine candidate JBK70 and its hlyA::KmR mutant suggest that HlyA* may be responsible for the residual diarrhoea observed in cholera-toxinless vaccine strains.

Animals↗

PubMed1991

Mucosal immune activation and maturation of the small intestine at weaning in the hypothymic (nude) rat.

Activation of the mucosal immune system peaks at weaning on days 21 and 22 of life in the rat. We have investigated activation in the gut associated lymphoid tissue and maturation of intestinal mucosa in hypothymic (nude) and in phenotypically normal heterozygous CBH rats at 22 days of life. Intestinal maturation, as assessed by villus area, crypt length, crypt cell production rate and disaccharidase activity, was similar in hypothymic and normal rats, and indices of mucosal immune function were elevated in both groups at this time. The proportion of mononuclear cells from the mesenteric lymph node expressing IL-2R was 11% in heterozygous and 14% in hypothymic rats as determined by flow cytometry. Immunoperoxidase staining of MLN sections confirmed the presence of IL-2R+ cells in the T-dependent interfollicular areas. However, the number of T-cells was considerably depleted in hypothymic rats. Intraepithelial lymphocyte counts and serum rat mucosal mast cell protease II concentrations were similar in the two groups, while counts of jejunal mucosal mast cells and eosinophils were paradoxically increased in hypothymic animals. As T lymphocyte function is thought to be impaired in hypothymic rats, the intact mucosal immune activity in hypothymic rats could be due to activation of intrinsic "thymic independent" T lymphocytes in hypothymic rats, or to engraftment with extrinsic maternal milk-derived lymphocytes and their activation in the infant rat gut.

Animals↗

PubMed1990

[AIDS of the central nervous system].

The central nervous system of nearly every HIV-positive patient becomes affected by the AIDS virus itself or by one of the associated diseases during the course of the illness. Early diagnosis of lesions which demand therapeutic consequences is of the most importance concerning prolongation of life and improvement in its quality. In spite of the frequent underestimation of cerebral involvement by imaging methods and their unspecific findings they are often the only diagnostic means which permit-timely diagnosis and, at least in some diseases, therapeutic monitoring. Indications for cranial computed tomography (CCT) or magnetic resonance tomography (MRT) are already present with mild or transient neurological or psychiatric symptoms or the extracerebral manifestation of neurotropic organisms or tumours which metastasize to the brain, even in patients without subjective complaints.

AIDS Dementia Complex↗

PubMed1990

Role of the P plasmid in attenuation of Vibrio cholerae O1.

The conjugative plasmid P of Vibrio cholerae has been shown to have a suppressive effect on the virulence of hypertoxigenic strains like 569B. In this study, we have sought to analyze this phenomenon. Utilizing the infant mouse cholera model, we have demonstrated that the presence of P increases the 50% lethal dose of V. cholerae classical Inaba 569B by more than 300-fold. No effect of P on cholera toxin (CT) production, whether measured by GM1 enzyme-linked immunosorbent assay, by CT activity in ligated rabbit ileal loops, or by transcription from the CT promoter, could be discerned. Colonization of the intestine by P+ derivatives was dramatically reduced although only a minor effect could also be demonstrated on in vitro attachment to intestinal strips. Electron microscopic examination suggested that the P plasmid was affecting the production of the TCP pilus. Another conjugative plasmid, V, has also been examined, but it had no effect on virulence.

Animals↗

PubMed1990

Distribution of class II major histocompatibility antigens in enterocytes of the rat jejunum and their association with organelles of the endocytic pathway.

The subcellular distribution of class II major histocompatibility molecules has been investigated in enterocytes in the rat jejunum. Studies have been carried out at both light microscope and ultrastructural levels using an indirect immunoperoxidase technique and monoclonal antisera against rat class II molecules. The results show that the class II molecules have also been demonstrated on the baso-lateral cell membranes of enterocytes, but are absent from the brush borders. The distribution of class II molecules has also been studied during enterocyte maturation. The results suggest that enterocytes might be capable of intracellular processing of antigens and suggest that the encounter between class II molecules and processed antigens within the endocytic pathways of cells may be a general phenomenon in both 'professional' and 'non-professional' antigen-presenting cells.

Animals↗

PubMed1989

Giardia intestinalis: electrophoretic evidence for a species complex.

The technique of allozyme electrophoresis was applied to 29 Australasian stocks and 48 clones of Giardia intestinalis from humans as a means of increasing the number of genetic markers currently available for identification and classification. Fifty different enzymes were examined and of these 26 loci were found to be suitable for use as genetic markers. The data indicate the presence of four discrete genetic groups within the sample of G. intestinalis examined. The groups had fixed genetic differences at 23-69% of loci established. The evidence suggests that G. intestinalis is a species complex. The results have important implications for the systematics of human isolates of Giardia, as well as for studies on the epidemiology and demography of giardiasis in Australia and elsewhere.

Animals↗

PubMed1989

Genetic studies on nucleolus organizer regions (NORs) in cattle.

Experimentally produced monozygotic twins, natural opposite sex blood chimeras (freemartins), and several pedigrees were used to evaluate the genetic influences on the nucleolus organizer region (NOR) patterns in cattle. In monozygotic twins, the NOR patterns of both twins are extremely similar. In chimeras, NOR patterns of genetically identical, peripheral blood lymphocytes (PBL) from the two partners resemble each other. In contrast, genetically different PBL (sib organ) differ significantly in the same environment. A high heritability of the individual NOR patterns is also demonstrated in our 23 pedigrees. In conclusion, our data demonstrate that variation in NOR expression is predominantly due to genetic factors.

Animals↗

PubMed1989

Subcellular distribution of class II major histocompatibility antigens in enterocytes of the human and rat small intestine.

Class II antigens encoded within the major histocompatibility complex (MHC) have been examined at the ultrastructural level in enterocytes from both man and rat. A protocol has been developed for fixation which, in conjunction with a pre-embedding indirect immunoperoxidase technique preserves antigenicity of the class II molecules and allows detection of intracellular antigen. Details of the technique are provided and discussed in relation to the general paucity of information available on ultrastructural localization of class II MHC molecules. Class II MHC antigens have been identified on the basolateral cell membranes of enterocytes in both species and they have also been found in association with intracellular organelles that have the appearance of multivesicular bodies and secondary lysosomes. These observations link class II molecules with the endocytic pathway in enterocytes and suggest a possible role in the handling of gut antigens. The findings may have a more general significance in relation to the site of engagement between processed antigen and MHC molecules in specialized antigen-presenting cells.

Animals↗

PubMed1988

A comparative study of infections with rodent isolates of Giardia duodenalis in inbred strains of rats and mice and in hypothymic nude rats.

Giardia isolated from mice and rats have been identified as Giardia duodenalis by morphological criteria. No differences in the electrophoretic mobilities of 28 enzymes were detected between the mouse and rat isolates or between these isolates and human and cat isolates. Infections with both rodent isolates have been studied in several strains of inbred rats. No significant differences were detected between the rat strains, with the mouse isolate producing a self-limiting infection and the rat isolate a chronic infection. After the primary infection was eradicated with metronidazole, all strains of rats were resistant to reinfection with the homologous isolate. Both isolates produced chronic infections in hypothymic nude rats. BALB/c mice were found to be relatively resistant to primary infection with either isolate but C3H mice became infected chronically with the mouse isolate and experienced a prolonged infection with the rat isolate. These findings resemble those observed with infections with G. muris in the same strains of mice (Roberts-Thomson & Mitchell 1978). It is suggested that infections with G. duodenalis in rats may offer a model for giardiasis that is based on organisms related closely to G. lamblia. Comparative studies using the two rodent isolates may lead to a better understanding of how the parasite establishes as a chronic infection and which antigens induce protective immune responses.

Acute Disease↗

PubMed1988

Biliary antibody response in rats infected with rodent Giardia duodenalis isolates.

Using a sensitive ELISA, specific serum and bile anti-Giardia IgM and IgA responses were studied in rats infected with two strains of Giardia duodenalis: a rat isolate which produces a chronic infection and a mouse isolate which produces a self-limiting infection. Paired samples of serum and bile were collected from groups of DA (RT1avl) rats at various times during primary and secondary infections. Antibody responses to both organisms were similar. Only IgA anti-Giardia antibodies were detected in bile whereas both IgM and IgA antibodies were detected in serum. Biliary IgA antibody titres increased throughout the course of the primary infection and remained at high levels for at least 10 weeks. Biliary IgA titres increased 16-fold during the secondary infection with both isolates. Serum IgA anti-Giardia titres also increased but more slowly than the titres in bile. Serum IgM antibody responses were observed against both organisms during the primary and secondary infections. Trophozoites harvested from the intestinal lumen during primary infections were examined for surface-bound IgA by immunofluorescence microscopy. IgA was detected on 3% of trophozoites on day 7 after infection but on over 70% of trophozoites by the 10th day. The data demonstrate the occurrence of a secretory IgA immune response in rats infected with both G. duodenalis isolates, some of which is directed against surface antigens of the trophozoites.

Animals↗

PubMed1987

Specificity of a mouse monoclonal antibody raised against acute myeloid leukaemia cells for mast cells in human mucosal and connective tissues.

A mouse monoclonal antibody raised against acute myeloid leukaemia cells (YB5.B8 monoclonal antibody; Gadd, S. J. and Ashman, L. K. (1985): Leukaemia Res. 9, 1329-1336) has been found by an indirect immunoperoxidase technique to bind to scattered cells in frozen sections from a number of human tissues. They have been identified as mast cells in fixed sections of skin, tonsil and duodenum by simultaneous staining of glycosaminoglycan with Alcian blue in 0.7 N HCl. The antibody does not distinguish mast cells in mucosal tissues from those in connective tissue, although the level of expression by cells at both sites appears to be heterogeneous. With the exception of low affinity binding to B lymphocytes, no other bone marrow-derived cells were found to bind the antibody. In particular, basophils and eosinophils were not stained, suggesting that they are not related closely to mast cells and that the antigen detected by YB5.B8 monoclonal antibody is not an IgE Fc receptor. Therefore, among all mature haemopoietic lineages, the antibody is specific for mast cells.

Animals↗

PubMed1986

Potentiated IgE response in Nippostrongylus brasiliensis infested rats--sites of synthesis and traffic of cells secreting potentiated antibody.

The distribution and the kinetics of potentiated antibody synthesis have been studied at the cellular level in rats infested with Nippostrongylus brasiliensis using the homologous adoptive cutaneous anaphylaxis technique. In animals immunized in the hind footpads with alum-absorbed ovalbumin 10 days prior to infestation with the parasite, the major sites of potentiated anti-ovalbumin homocytotropic antibody synthesis were the regional lymph nodes of the gut and the lungs. Peyer's patches were weakly active late in the response and the spleen produced considerable amounts of potentiated antibody. The regional lymph nodes of the ovalbumin immunization sites were the only organs in which specific homocytotropic antibody synthesis was detected in uninfested control rats. The kinetics of synthesis of the potentiated antibody by cells correlated well with the levels of anti-ovalbumin IgE antibodies in the sera of the infested rats. A traffic of cells secreting anti-ovalbumin homocytotropic antibody was detected in the thoracic duct lymph, but not the mesenteric lymph of immunized uninfested rats. After infestation, the mesenteric lymph also contained cells secreting potentiated antibody. The mesenteric lymph is a major route by which IgE and potentiated IgE antibodies reach the circulation in infested rats. The possible mechanisms responsible for the effects of the parasite on antibody secretion in distant lymphoid organs are discussed.

Animals↗