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  • Title: The epithelium covering Peyer's patches in young milk-fed calves. An ultrastructural and enzyme histochemical investigation.
    Author: Landsverk T.
    Journal: Acta Vet Scand; 1981; 22(2):198-210. PubMed ID: 7304361.
    Abstract:
    Between the ordinary villi over Peyer’s patches there are small domes or “pseudovilli” caused by bulges in the lymphoid tissue. These “pseudovilli” were studied in 5 healthy milk-fed, about 3-week-old, pre-ruminant calves. Scanning electron microscopy revealed that the “pseudovilli” were covered by a specialized follicle associated epithelium (FAE). The FAE had poorly developed microvilli and often extensive folding of the cell surface close to the cell borders. By transmission electron microscopy the tips of the marginal folds of the FAE seemed to fuse, probably in the process of enfolding bulk material from the lumen. The FAE apical cytoplasm contained numerous thick-walled and bristle-coated invaginations, tubules and vesicles indicative of micropinocytosis. Multivesicular bodies and large vacuoles were frequent. Indications of extracellular unloading of residual bodies were found. Intraepithelial lymphocytes tended to group together, and some were rich in rough endoplasmic reticulum. Enzyme histochemistry showed weak reactions of adenosine triphosphate splitting enzyme and aminopeptidase in the FAE luminal cell border. Cytoplasmic acid phosrphatase showed a marked basal-apical decrease along the “pseudovillus” probably caused by the onset of endocytosis. The results of this study appear compatible with the concept that the FAE takes up macromolecules from the lumen by pinocytosis and sensitizes lymphocytes. Mellom de ordinære villi over Peyerplettene hos unge kalver er det små fremhvelvninger av lymfoid vev. Disse fremhvelvninger eller „pseudovilli“ ble studert hos 5 friske, omkring 3 uker gamle, melkeförede kalver. Skanning elektron mikroskopi viste at „pseudovilli“ var utkledt av et spesialisert follikel-assosiert epitel (FAE) som hadde sparsom utvikling av mikrovilli og karakteristiske konsentriske folder i den luminale celleoverflate. Transmisjonselektronmikroskopisk undersøkelse tydet på at disse foldene kunne smelte sammen og inkorporere partikler i cytoplasmaet. Invaginasjoner av cellemembranen var hyppige, spesielt under foldene. Noen invaginasjoner viste tydelige „børster“ på cytoplasmaoverflaten, et forhold som ble tatt til inntekt for en slik pinocyttose. Vakuoler, multivesikulære legemer og residuallegemer forekom ofte i FAE; noen ganger syntes innholdet i residuallegemene å bli avlevert til intercellulærspaltene ved eksocyttose. Intraepitheliale lymfocytter opptrådte ofte gruppevis og noen hadde rikelig med endoplasmatisk retikulum. Enzymhistokjemi ga svake reaksjoner av adenosin trifosfat-sp alten de enzym og aminopeptidase i FAE’s celleoverflate. Sur fosfatase i cytoplasma av FAE viste en markert reduksjon fra basis til apicale partier av „pseudovilli“, antagelig i forbindelse med endocyttose. Resultatene fra dette studiet synes forenlige med den oppfatning at FAE pinocytterer makromolekyler og sensiterer lymfocytter.
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