ABSTRACT
In pathogenesis of celiac disease, the significance of prolamin peptide interactions with enterocytes is controversial. Changes in cellular metabolism induced by gliadin peptides, as well as uptake and presentation by enterocytes, are discussed. We analyzed peptide binding to enterocytic membranes as a potential key event. Binding capacities of brush border membranes isolated from small intestinal biopsies of untreated (n = 49) and treated celiac patients on a gluten-free diet (n = 30), as well as control subjects (n = 43), were measured with a dot blot chemiluminescence assay. Synthetic gliadin peptides comprising amino acid position 8-19 (G XIV) and 30-41 (G XI) of alpha-gliadins, a peptic-tryptic digest of gliadin (PT-GLI), and a synthetic zein peptide were used. Comparing treated celiac patients with controls, we observed significantly enhanced membrane-binding of PT-GLI [mean 122.4 densitometric units/microg (95% confidence interval 116.0-128.9) vs 108.9 (102.1-115.7)] and of zein peptide [50.2 (38.4-61.9) vs 28.8 (13.4-44.2)], but only slightly increased binding of the synthetic gliadin peptides G XIV [65.5 (60.6-70.5) vs 62.4 (56.3-68.5) and G XI [75.2 (69.8-80.6) vs 65.9 (55.2-76.5)]. Independent of patient group, membrane-binding capacities for celiac-active gliadin peptides exceeded those of the zein peptide. Thus, interaction of gliadin peptides with the apical enterocytic membrane was not found exclusively in celiac disease. Furthermore, increased binding capacities in treated celiac disease were not confined to celiac-active peptides. Quantitative differences in gliadin peptide binding as a primary characteristic in celiac disease might contribute to pathogenetic effects exerted on small intestinal epithelial cells.
Subject(s)
Celiac Disease/metabolism , Gliadin/metabolism , Intestine, Small/metabolism , Microvilli/metabolism , Adolescent , Celiac Disease/pathology , Child , Child, Preschool , Female , Humans , Infant , Intestine, Small/ultrastructure , Male , Peptides/metabolism , Protein BindingABSTRACT
A comparison between the intestinal epithelial cell lines Caco-2 and T84 was made to assess the influence of enterocytic differentiation on food protein binding capacities of the brush border membrane. Cell morphology and expression of brush border-associated enzymes were studied as differentiation markers. Food protein binding to isolated brush border membranes was measured with a dot blot chemiluminescence assay. Early at confluence, Caco-2 cells exhibited a more differentiated state compared to T84 cells. Brush border membranes of both cell lines bound gliadin peptides, beta-lactoglobulin and ovalbumin specifically. Binding capacities increased from gliadin peptides to ovalbumin to beta-lactoglobulin. There was correlation of membrane binding capacity with degree of cell differentiation. Due to their similarity to small intestinal epithelial cells, the colon carcinoma cell lines Caco-2 and T84 represent models for studying food protein-enterocytic brush border membrane interactions in relation to varying degrees of cell differentiation.
Subject(s)
Dietary Proteins/metabolism , Intestinal Mucosa/metabolism , Microvilli/metabolism , Caco-2 Cells , Cell Differentiation , Cell Line , Colonic Neoplasms/metabolism , Epithelial Cells/metabolism , Freeze Fracturing , Gliadin/metabolism , Humans , Lactoglobulins/metabolism , Luminescent Measurements , Microscopy, Electron , Ovalbumin/metabolismABSTRACT
Diffraction efficiencies of 44.8-5.4-A x rays by a free-standing gold transmission grating of 1.0-microm period have been measured, using characteristic line radiation. Partial transparency of the grating affects the efficiency at the shorter wavelengths and causes an increase in the efficiencies for orders m>/=1 over the longwavelength values. Model calculations for a trapezoidal wire cross section are in good agreement with the measured efficiencies and allow the wire cross section to be determined. Gratings of this type have a high efficiency for wavelengths as short as 5 A and are, therefore, well suited for applications both in x-ray and extreme uv astronomy.
ABSTRACT
The manufacturing process of open transmission gratings with high efficiency and high line density is described. This process is developed by Dr. Johannes Heidenhain GmbH in cooperation with the Max- Planck-Institut and involves two steps, the mechanical ruling of the original master and the photochemical replication of the individual grating facets. The freestanding transmission grating is added by a regular support structure obstructing about one-third of the grating area. For application in space astronomy, gratings have been subjected to vibration and acoustic-noise tests.
ABSTRACT
The aberrations of various types of curved constant-period transmission gratings are discussed, using Fermat's principle. We show that optimal performance is achieved with a grating assembled from individual facets which form a nonclosed surface. For this geometry, primary coma and astigmatism are proportional to the facet size and, hence, may be adapted to the angular resolution of a Wolter-type telescope.
ABSTRACT
Third-order aberrations are discussed of a transmission grating positioned behind a Wolter type I telescope, using Fermat's principle. We describe the conditions required to obtain a coma-free grating. The performance of a grating spectrometer for cosmic x-ray spectroscopy is discussed in some detail.
