Development of Accessory Cells in B-Cell Compartments Is Retarted in B-Cell-Depleted Fetal Sheep

Accessory-cell populations in the lymphoid tissues of fetal sheep were investigated following depletion of B cells. An intraperitoneal injection of an anti-IgM antibody early in gestation resulted in a marked depletion of IgM+ cells in lymphoid tissues. Immune and enzyme histochemical techniques were used to identify accessory-cell populations in the ileal Peyer's patch, spleen, and lymph nodes of B-cell-depleted fetal sheep. The rudimentary follicles in the ileal Peyer's patch showed strong enzyme reactivity for 5′ nucleotidase, indicating the presence of follicular dendritic cells (FDCs). Enzyme reactivities for FDCs in primary follicles of the spleen and lymph nodes were absent, as were reactivities for metallophilic macrophages in the marginal zone of the spleen. MgATPase reactivity associated with dendritic-cell populations in the gut-associated lymphoid tissues was detected. A monoclonal antibody against complement receptor-2 (CD21) reacted with FDCs in the rudimentary follicles of the ileal Peyer's patch and immature FDCs in lymph nodes. The results suggest that the development of accessory-cell populations in B-cell compartments of peripheral but not central lymphoid tissues is dependent on the presence of B cells

PrP Expression, PrPSc Accumulation and Innervation of Splenic Compartments in Sheep Experimentally Infected with Scrapie

BACKGROUND: In prion disease, the peripheral expression of PrP(C) is necessary for the transfer of infectivity to the central nervous system. The spleen is involved in neuroinvasion and neural dissemination in prion diseases but the nature of this involvement is not known. The present study undertook the investigation of the spatial relationship between sites of PrP(Sc) accumulation, localisation of nerve fibres and PrP(C) expression in the tissue compartments of the spleen of scrapie-inoculated and control sheep. METHODOLOGY/PRINCIPAL FINDINGS: Laser microdissection and quantitative PCR were used to determine PrP mRNA levels and results were compared with immunohistochemical protocols to distinguish PrP(C) and PrP(Sc) in tissue compartments of the spleen. In sheep experimentally infected with scrapie, the major sites of accumulation of PrP(Sc) in the spleen, namely the lymphoid nodules and the marginal zone, expressed low levels of PrP mRNA. Double immunohistochemical labelling for PrP(Sc) and the pan-nerve fibre marker, PGP, was used to evaluate the density of innervation of splenic tissue compartments and the intimacy of association between PrP(Sc) and nerves. Some nerve fibres were observed to accompany blood vessels into the PrP(Sc)-laden germinal centres. However, the close association between nerves and PrP(Sc) was most apparent in the marginal zone. Other sites of close association were adjacent to the wall of the central artery of PALS and the outer rim of germinal centres. CONCLUSIONS/SIGNIFICANCE: The findings suggest that the degree of PrP(Sc) accumulation does not depend on the expression level of PrP(C). Though several splenic compartments may contribute to neuroinvasion, the marginal zone may play a central role in being the compartment with most apparent association between nerves and PrP(Sc)

Exosome-Producing Follicle Associated Epithelium Is Not Involved in Uptake of PrPd from the Gut of Sheep (Ovis aries): An Ultrastructural Study

In natural or experimental oral scrapie infection of sheep, disease associated prion protein (PrPd) often first accumulates in Peyer's patch (PP) follicles. The route by which infectivity reaches the follicles is unknown, however, intestinal epithelial cells may participate in intestinal antigenic presentation by delivering exosomes as vehicles of luminal antigens. In a previous study using an intestinal loop model, following inoculation of scrapie brain homogenate, inoculum associated PrPd was detected by light microscopy shortly (15 minutes to 3.5 hours) after inoculation in the villous lacteals and sub-mucosal lymphatics. No PrPd was located within the follicle-associated epithelium (FAE), sub-FAE domes or the PP follicles. To evaluate this gut loop model and the transportation routes in more detail, we used electron microscopy (EM) to study intestinal tissues exposed to scrapie or control homogenates for 15 minutes to 10 days. In addition, immuno-EM was used to investigate whether exosomes produced in the FAE may possess small amounts of PrPd that were not detectable by light microscopy. This study showed that the integrity of the intestinal epithelium was sustained in the intestinal loop model. Despite prominent transcytotic activity and exosome release from the FAE of the ileal PP in sheep, these structures were not associated with transportation of PrPd across the mucosa. The study did not determine how infectivity reaches the follicles of PPs. The possibility that the infectious agent is transported across the FAE remains a possibility if it occurs in a form that is undetectable by the methods used in this study. Infectivity may also be transported via lymph to the blood and further to all other lymphoid tissues including the PP follicles, but the early presence of PrPd in the PP follicles during scrapie infection argues against such a mechanism

Development of Accessory Cells in B-Cell Compartments Is Retarted in B-Cell-Depleted Fetal Sheep

Accessory-cell populations in the lymphoid tissues of fetal sheep were investigated following depletion ofB cells. An intraperitoneal injection of an anti-IgM antibody early in gestation resulted in a marked depletion of IgM+cells in lymphoid tissues. Immune and enzyme histochemical techniques were used to identify accessory-cellpopulations in the ileal Peyer's patch, spleen, and lymph nodes of B-cell-depleted fetal sheep. The rudimentaryfollicles in the ileal Peyer's patch showed strong enzyme reactivity for 5′ nucleotidase, indicating the presenceof follicular dendritic cells (FDCs). Enzyme reactivities for FDCs in primary follicles of the spleen and lymph nodeswere absent, as were reactivities for metallophilic macrophages in the marginal zone of the spleen. MgATPasereactivity associated with dendritic-cell populations in the gut-associated lymphoid tissues was detected.A monoclonal antibody against complement receptor-2 (CD21) reacted with FDCs in the rudimentary follicles ofthe ileal Peyer's patch and immature FDCs in lymph nodes. The results suggest that the development of accessory-cellpopulations in B-cell compartments of peripheral but not central lymphoid tissues is dependent on the presence of B cells.Peer Reviewe

Response of Leucocyte Populations in the Ileal Peyer's Patch of Fetal Lambs Treated with Ferritin Per Os

A combination of immunohistochemical techniques, a panel of monoclonal antibodies, and computer-assisted morphometric analysis was used to examine the response of the ileal Peyerr's patch of fetal lambs 7 days after treatment with ferritin per os. Consistent with previous studies in fetal lambs that have reported the ileal Peyer's patch to be indifferent to antigen, the present study did not find any significant changes in the size of the predominantly B-cell dome/follicle compartment or the predominantly T-cell interfollicular area, nor were differences identified in the distribution of IgM-positive (+), CD4 +, and CD8+ cells in these two compartments. However, both compartments showed a significant increase (P < 0.05) in the percentage of area occupied by MHC II + cells and a significant decrease (P < 0.05) in the percentage of area occupied by CD44+ and B5+ cells. These changes show that the ileal Peyer’s patch of fetal lambs is not indifferent to antigen and may represent the transition of a purely primary lymphoid organ to an organ that has both primary and secondary lymphoid functions

NCR1+ cells appear early in GALT development of the ovine foetus and acquire a c-kit+ phenotype towards the end of gestation

International audienceThe amount, distribution and phenotype of ovine NCR1+ cells were investigated during developing GALT from day 70 of gestation. Antibodies against CD3 and CD79 were used to identify the compartments of GALT, and the localization of NCR1+ cells were correlated within these structures. Markers CD34 and c-kit, in addition to Ki67, were used to investigate possible origin and the stage of development of the NCR1+ cells. NCR1+ cells were present as single cells in the subepithelial tissue as early as 70 days of gestation, and were predominantly present in the T cell rich IFAs and domes as these intestinal wall compartments developed. While NCR1+ cells proliferated more intensively at mid-gestation (70-104 days), the number of NCR1+ cells also expressing c-kit, increased at the end of gestation. In conclusion, NCR1+ cells appeared early in T cell areas of the gut and displayed a phenotype consistent with intermediate stages of cNK cells and/or a subpopulation of ILC22. (C) 2016 Elsevier B.V. All rights reserved

PrP mRNA expression in splenic compartments.

<p>PrP mRNA expression levels in compartments of spleen of five VRQ/VRQ lambs after oral inoculation with scrapie (black columns) and five control lambs (gray columns). The y axis represents mRNA levels relative to GAPDH expression obtained by real-time RT-PCR analysis. Error bars represent standard deviation. There was no significant difference in PrP mRNA levels between the scrapie-inoculated and control animals. The level of PrP mRNA expression in the red pulp (RP) was significantly higher than in all other tissue compartments, namely the periarterial lymphatic sheaths (PALS), lymphoid nodules (LN), marginal zone (MZ) and trabeculae (TR).</p

Immunohistochemistry for PrP^Sc.

<p>Scrapie inoculated sheep. Immunolabelling was most abundant in the light zone of the germinal centre (GC) but a few scattered strongly labelled cells were also present in the dark zone near the outer rim of the lymphoid nodule delineated by spindle-shaped cells (arrowheads, also in inset). In the marginal zone (MZ), an abundant finely granular labelling was prominent and in the PALS (P) a few medium-sized granules (arrow), often close to the arteriole (a), were labelled. RP: red pulp. Bar, 100 µm. Nuclei were stained with haematoxylin.</p

Immunohistochemistry, double labelling for PrP^Sc (<i>brown colour</i>) and nerves (<i>PGP, red colour</i>).

<p>Scrapie inoculated sheep. A, B. In the germinal centres (GC), a few nerve fibres were present in close association with cells strongly immunolabelled for PrP^Sc (A; inset). In some areas, the lymphoid nodules were separated from the PALS by a narrow rim of spindle-shaped cells (A, B; arrowheads) with PrP^Sc labelling mostly confined to the nodule side of the rim. In the PALS, nerves were most abundant around the arteriole (a), sometimes with PrP^Sc-labelled granules close to the nerve fibres (A; arrow). Among the lymphoid cells of the PALS, a few nerve fibres and small granules labelled for PrP^Sc were generally not co-localised. In the red pulp (A; RP) and the marginal zone (B; MZ), longitudinally and cross-sectioned small nerve fibres (B; white arrows) were abundant. C. High power view of B, showing the PALS-germinal centre transition (arrowheads), PGP labelled nerve fibres (white arrows) and PrP^Sc (black arrows). D. In the marginal zone, the nerve fibres (white arrow) were often close to numerous small granules labelled for PrP^Sc (black arrows). Bars, 100 µm (A, B), 10 µm (C, D). Nuclei were stained with haematoxylin.</p