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A Behrens

Publications and source records attributed to A Behrens.

46 records · Page 3Linked to original sources
PubMed1996

Immunoelectron microscopic localization of variable proteins on the surface of Mycoplasma bovis.

The ultrastructural distribution and immunological accessibility of the variable surface proteins VspA, VspB, VspC and VspD were determined by immunoelectron microscopy on the surface of negatively stained cells of Mycoplasma bovis PG45 and 18 subclones, expressing either one or two of the Vsps. The variable proteins VspA, VspB, VspC and VspD, recognized by two monoclonal antibodies (mAb 1E5 and mAb 87-2) and visualized by goat-anti-murine-lgM labelled with gold particles, showed identical distribution patterns on the surfaces of the cells of all M. bovis clones investigated. Gold particles were distributed over the whole cell surface, arranged in clusters. The cell form seemed not to have an influence on the decoration pattern. Gold particles were also observed in irregular distributions around the cells. All clones showed unlabelled cells as well as strongly and weakly labelled cells. There were in general, however, no significant differences in the percentages of unlabelled, weakly labelled and strongly labelled cells, either between clones expressing different Vsps or between individual clones. No correlations were found between the numbers of labelled cells in immunoelectron microscopy and the numbers of labelled colonies in immunobinding assay (IBA) originating from the same broth cultures. The percentage of positive colonies in IBA was generally much higher than the percentage of positive cells in immunoelectron microscopy. The results show that the cells of the M. bovis clones are not identical, but differ in their surface antigens, and reveal the high variable potential of this species.

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PubMed1994

Antigen heterogeneity among isolates of Mycoplasma bovis is generated by high-frequency variation of diverse membrane surface proteins.

The protein and antigen profiles of 11 isolates of Mycoplasma bovis were compared by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblot analysis of whole organisms. The isolates examined included the type strain PG45 and 10 other filter-cloned strains or purified isolates both from animals without clinical signs and from clinical cases of bovine mastitis, arthritis, or pneumonia. While the overall protein patterns visualized by silver staining were very similar, marked differences in the antigen banding profiles were detected by rabbit antiserum prepared against whole organisms from one of the strains analyzed. This antigenic heterogeneity was shown to be independent of the geographical origin, the type of clinical disease, and the site of isolation and was also observed among serial isolates from a single animal. Antigen profiles were further monitored throughout sequentially subcloned populations of the PG45 strain. This clonal analysis revealed a high-frequency variation in the expression levels of several prominent antigens. All of these variable antigens were defined by detergent-phase fractionation with Triton X-114 as amphiphilic integral membrane proteins. A subset of different-sized membrane proteins was identified by a monoclonal antibody raised against a PG45 subclone expressing a 63- and a 46-kDa variant antigen within that set. The selective susceptibility of these proteins to trypsin treatment of intact organisms and their ability to bind the monoclonal antibody in colony immunoblots demonstrated that they were exposed on the cell surface. In addition, their preferential recognition by serum antibodies from individual cattle with naturally induced M. bovis mastitis or arthritis confirmed that they were major immunogens of this organism. These studies establish that the apparent antigenic heterogeneity among M. bovis isolates reported here does not represent stable phenotypic strain differences generated from accumulated mutational events but reflects distinct expression patterns of diverse, highly variable membrane surface proteins.

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PubMed1994

A family of phase- and size-variant membrane surface lipoprotein antigens (Vsps) of Mycoplasma bovis.

A set of strain- and size-variant highly immunogenic membrane surface protein antigens of Mycoplasma bovis, which has been identified by a monoclonal antibody, is shown in this report to make up a family of antigenically and structurally related lipid-modified proteins, designated Vsps (variable surface proteins). By systematic analysis of several isogenic clonal lineages of the type strain PG45, three members of this family have been identified, VspA, VspB, and VspC, each of which was shown to undergo independent high-frequency changes in size as well as noncoordinate phase variation between ON and OFF expression states. The monoclonal antibody-defined epitope common to VspA, VspB, and VspC was accessible on the cell surface in most, but not all, of the clonal populations analyzed and was present on a C-terminal limit tryptic fragment of each Vsp variant that was released from the membrane surface. VspA and VspC were distinguished from VspB by their selective detection with colloidal gold and by their distinctive reaction with a polyclonal antibody against M. bovis D490. VspA, VspB, and VspC were further distinguishable from one another by their characteristic patterns of degradation at carboxypeptidase Y pause sites. While these Vsp-specific structural fingerprints with an irregular periodic spacing were constant for similarly sized variants of a defined Vsp product, they showed distinct differences among variants differing in size. This variability included gain or loss of individual bands within distinct subsets of bands, as well as shifts of the entire banding patterns up- or downwards, indicating that insertions or deletions underlying Vsp size variation can occur at various locations either within the C-terminal domain or within other regions of these proteins. This was similarly confirmed by comparative epitope mapping analysis of tryptic cleavage products generated from different Vsp size variants. The Vsp family of M. bovis described in this study represents a newly discovered system of surface antigenic variation in mycoplasmas displaying features which closely resemble but are also different from the characteristics reported for the Vlp (variable lipoprotein) system of M. hyorhinis. The isogenic lineages established here provide key populations for subsequent analysis of corresponding genes to further elucidate Vsp structure and variation, which may have important relevance for a better understanding of the pathogenicity of this agent.

Animals↗
PubMed1982

Lactose absorption and malabsorption in healthy German children: improved phenotypic resolution by simultaneous determination of breath hydrogen and carbon dioxide.

A total of 124 apparently healthy German children aged 8 to 10 years were examined for lactose absorption employing the breath hydrogen test with multiple breath collection. Analysis of the maximal change of breath hydrogen concentration (delta maxH2) 110 and 150 min after a lactose load of 30 g failed to yield a bimodal distribution separating lactose absorbers and malabsorbers as observed in adults. Comparison with an adult control group of 120 subjects showed that the mean CO2 concentration was significantly lower and the coefficient of variation was considerably higher in the breath samples of the children. The difference between the highest and the lowest CO2 concentration in the three samples obtained from each individual was also significantly higher in the group of children. Normalizing the children's H2 concentration values to the mean CO2 concentration in the total group (3.04%) yielded a bimodal distribution of the delta maxH2 values. Of 124 children, 18 were identified as lactose malabsorbers. The 14.5% frequency is similar to that observed in German adults.

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PubMedDate not supplied

Transient induction of 7-ethoxyresorufin-O-deethylase (EROD) activity by medium change in the rainbow trout liver cell line, RTL-W1.

Cytochrome P4501A (CYP1A) metabolizes a wide array of lipophilic xenobiotics. In fish liver, CYP1A is constitutively expressed at low levels, but xenobiotics can strongly induce CYP1A expression via a receptor-mediated pathway. While induction of hepatic CYP1A in teleosts by xenobiotics is well investigated, very little is known on the regulation of constitutive CYP1A expression and its induction by factors other than xenobiotics. In the present study we show that in the rainbow trout liver cell line, RTL-W1, CYP1A-catalyzed 7-ethoxyresorufin-O-deethylase (EROD) activity can be induced by a change of the culture medium, in the absence of xenobiotics. The increase in cellular EROD levels is of transient nature. Experiments with cell incubation solutions supplemented with various medium components indicate that photooxidized tryptophan is the agent causing the increase of EROD activity after medium change.

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PubMedDate not supplied

Evaluation of corneal flap dimensions and cut quality using a manually guided microkeratome.

BACKGROUND: To evaluate reproducibility of corneal flap dimensions and cut quality with repeated blade use with a manually guided microkeratome in pig eyes. METHODS: Corneal flaps were created using a manually guided microkeratome (Model One, Moria) with an intended 130-microns cut depth in 130 enucleated pig eyes. Flap thickness was calculated by pachymetry and diameter was estimated by means of applanation lenses compared to planimetry. Histology and scanning electron microscopy of samples and blades were performed to evaluate the keratectomy surface and blade cutting edge after repeated use of the blades. RESULTS: Mean flap central thickness was 135 microns (SD, 37 microns). The mean diameter of 8.4 mm (SD, 0.4 mm) correlated significantly (P < .001) to the intended diameter (r = .79). Mean difference from the intended diameter was 0.8 mm (SD, 0.3 mm; range, 0.04 to 1.4 mm). Scanning electron microscopy showed even and smooth cuts with chatter lines at the keratectomy edge using new blades. After repeated blade use, increasing cut irregularity, folds, and tissue remnants on the corneal bed surface, and nicks and tissue remnants at the cutting edge of the blades were observed. CONCLUSION: Reproducible flap dimensions were obtained using the Moria One microkeratome on pig eyes. The cut surface was regular and smooth with a new blade, but surface quality deteriorated considerably after repeated use of the same blade.

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PubMedDate not supplied

Evaluation of corneal flap dimensions and cut quality using the Automated Corneal Shaper microkeratome.

PURPOSE: To evaluate flap dimensions and cut deterioration with repeated blade use in an automated microkeratome. METHODS: The Automated Corneal Shaper (Chiron-Adatomed, Munich, Germany), 160-microm plate attached, was used to make a corneal flap in 90 pig cadaver eyes, reusing blades up to five times. Flap diameter was measured by planimetry and thickness was calculated by ultrasound pachymetry. Scanning electron microscopy of stromal beds and blade cutting edges was performed to assess cut deterioration after repeated blade use. RESULTS: Mean flap central thickness was 125 +/- 32 microm. Mean vertical flap diameter was 7.6 +/- 0.4 mm. No correlation was found between thickness and diameter (r = 0.15, P = .45). Progressive thinning of the flap was observed in the direction of the flap hinge. Smooth cuts (using new blades) with periodic chatter lines at the keratectomy edge and in the stromal bed were observed with scanning electron microscopy. Increasing tissue remnants on the stromal bed and decreasing cut quality occurred with repeated blade use. Blades showed larger tissue remnants, nicks, and even folds on the cutting edge proportional to the number of times blades were used. CONCLUSION: Satisfactory cut quality and reproducibility were obtained after a single use of stainless steel blades in the Automated Corneal Shaper microkeratome. Cut quality was degraded dramatically by repeated use of blades.

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