The aim of this immunocytochemical study was to compare mannose-binding lectin (MBL) production induced by avian coronavirus in the spleen and caecal tonsil (CT). One-day-old specific-pathogen-free (SPF) chickens were experimentally infected with six QX field isolates and the H120 vaccine strain. In the negative control birds, the spleen was MBL negative, while the CT showed scattered MBL-positive cells in close proximity and within the surface epithelium and germinal centre (GC)-like cell clusters. MBL was detectable in the ellipsoid-associated cells (EACs) and cell clusters in the periarterial lymphoid sheath (PALS) by 7 days post infection (dpi). In both organs, the MBL-positive cells occupy antigen-exposed areas, indicating that GC formation depends on resident precursors of dendritic cells. The majority of MBL-positive EACs express the CD83 antigen, providing evidence that coronavirus infection facilitated the maturation of dendritic cell precursors. Surprisingly, co-localisation of MBL and CD83 was not detectable in the CT. In the spleen (associated with circulation), the EACs producing MBL and expressing CD83 are a common precursor of both follicular (FDC) and interdigitating dendritic cells (IDC). In the CT (gut-associated lymphoid tissue, GALT) the precursors of FDC and IDC are MBL-producing cells and CD83-positive cells, respectively. In the CT the two separate precursors of lymphoid dendritic cells provide some 'autonomy' for the GALT.
In the medulla of bursal follicle, only the secretory dendritic cell (BSDC) is furnished with secretory machinery. The granular discharge of BSDC appears in membrane-bound and solubilized forms. Movat pentachrome staining proves that the solubilized form is a glycoprotein, which fills up the extracellular space of follicular medulla. The glycoprotein contributes to bursal microenvironment and may be attached to the surface of medullary lymphocytes. The secretory granules of BSDC may be fused, resulting in large, irregular dense bodies, which are the first sign of BSDC transformation to macrophage-like cells (Mal). To determine the effect of infectious bursal disease virus (IBDV) infection on the extracellular glycoprotein and BSDC, SPF chickens were experimentally infected with IBDV. On the surface of BSDC, the secretory substance is in high concentration, which may contribute to primary binding of IBDV to BSDC. The early distribution of IBDV infected cells is in consent with that BSDC. The IBDV infected BSDC rapidly transforms to Mal in which the glycoprotein staining appears. In the dense bodies, the packed virus particles inhibit the virus particles preventing the granular discharge, which may represent the first, early phase of virus replication cycle. The absence of extracellular glycoprotein results in alteration in the medullary microenvironment and subsequently B cell apoptosis. On the surface of medullary B cells, the solubilized secretory substance can be in much lower concentration, which results in secondary binding of IBDV to B cells. In secondary, late phase of virus replication cycle, the virus particles are not packed in electron dense substance which results in cytolytic lymphocytes and presence of virus in extracellular space. The Mal emigrates into the cortex, where induces inflammation, recruiting heterophil granulocyte and monocyte.
Abstract SCL, Lmo2 and GATA factors form common transcription complexes during hematopoietic differentiation. The overlapping expression of SCL with GATA‐2 and GATA‐3 in the developing brain indicated that these factors might collaborate also in the course of neural tissue differentiation. The expression pattern of Lmo2 in the developing CNS, however, is not well understood. Here, we show that neural cells in the early embryonic chick mid‐ and hindbrain express SCL and GATA‐2, while Lmo2 is expressed only in vascular elements. The lack of Lmo2 transcripts in neural cells demonstrated that SCL and GATA‐2 cannot form common complexes with Lmo2 in the developing brain. In the course of neural tissue genesis, GATA‐2 mRNA appeared prior to the SCL transcript. While GATA‐2 expression decreased with maturation, SCL expression persisted at a high level also in post‐neurogenic periods. The temporal pattern of SCL and GATA‐2/3 expression was investigated also in vitro, in the course of induced neurogenesis by NE‐4C neural stem cells. While GATA‐2 expression increased from the very beginning of differentiation, SCL expression appeared only in more differentiated cells expressing proneural genes. GATA‐3 expression, on the other hand, was detected only in advanced stages of the neuronal maturation, which were characterised by the activation of the Math2 neuronal gene. Similarly to the hematopoietic differentiation, GATA‐2 expression precedes the activation of both SCL and GATA‐3, and may play roles in the activation of the SCL gene in neuronal development. In contrast to hematopoietic differentiation, however, our results failed to demonstrate co‐assembling of GATA factors or SCL with Lmo2. While overlapping expression of GATA‐2/3 and SCL was detected, Lmo2 activation could not be demonstrated in neural cells in the investigated period of neuronal development.
In the chicken bursa of Fabricius (BF), the interfollicular epithelium (IFE) consists of cylindrical- and cuboidal-shaped cells. Among the cylindrical-shaped epithelial cells, mucus-producing and caveolin-1 (Cav-1)-expressing cells can be distinguished. Occasionally, the cuboidal-shaped cells also express Cav-1, which suggests that they are precursors of both mucus-producing and Cav-1-expressing cells. Very virulent infectious bursal disease virus (IBDV) impedes the differentiation of Cav-1-expressing cells and shifts the differentiation of cuboidal cells towards mucus-producing cells. In control birds exclusively, the IFE surface shows a mucous membrane, but after IBDV infection, the surfaces of both IFE and FAE are also covered by a mucous membrane. After IBDV infection, the cells of FAE also produce mucus, providing evidence for cell transformation. In late postinfection (pi; 28 d pi), the Cav-1 expression returned in the IFE cells, whereas the follicle (the primary lymphoid organ) underwent atrophy. The appearance of the renewed Cav-1-positive cells is similar to that of the normal basal cell, but they randomly locate in different levels of IFE, suggesting the loss of epithelial polarity. Between days 2 and 7 pi, the Cav-1 expression in the endothelial cells of the cortico-medullary capillary web is variable, which may explain the hemorrhage in several infected birds. The IBDV infection stops the Cav-1 expression and subsequently the cholesterol efflux into the bursal lumen. In the infected birds, the high cholesterol level may further worsen the clinical syndrome of IBDV.
The classical histological features of the thymus are the cortex and medulla, the Hassall's bodies as well as the lobules. Anti-pan-cytokeratin immunocytochemistry shows that the keratin staining pattern of the cortical and medullary epithelial cells is different. The medulla is further compartmentalized: it consists of keratin-positive network and keratin-negative areas. Histology of the keratin-negative area is identical with the connective tissue of the septae. The basal lamina is continuous at the capsule and septae, but it becomes discontinuous at the border between the keratin-positive network and keratin-negative area. This immunohistochemical finding is the first histological sign, which may explain that the medulla has no blood-thymus barrier. The supporting tissue of the keratin-negative area is identical with that of the septae. The connective tissue of thymic capsule and septae develops from the cranial neural crest cells, therefore we hypothesize that the keratin-negative area has neural crest origin. Blood vessels of the thymic medulla localize in the keratin-negative area. Every emigrating or immigrating immunologically competent cells should enter the keratin-negative area, therefore this area is the transit zone of the thymus. The hematoxylin-eosin staining of the thymus shows that the thymic cortico-medullary border does not represent cellular background. However, the border between keratin-positive network and keratin-negative area is determined by cellular identity (epithelial and mesenchymal tissues). Therefore, it can be assumed that the real histological and functional border is the border between the keratin-positive network and the keratin-negative area. Orv Hetil. 2019; 160(5): 163-171.Absztrakt: A thymus klasszikus hisztológiai tulajdonságai: a kéreg- és velőállomány, a Hassall-testek és a mirigyekre jellemző lebenyezettség. Az anti-páncitokeratin festése azt mutatja, hogy a kérgi és velőhámsejtek keratinmintázata különböző. A velőállomány további kompartmentekre különül: keratinpozitív hálózatra és keratinnegatív területre. A keratinpozitív hálózat összeköttetésben áll a kérgi hámreticulummal, míg a keratinnegatív terület folyamatos a septumok kötőszöveti állományával. A keratinnegatív területnek, a toknak és a septumnak a támasztószövete reticularis kötőszövet. A kéregállományt a tok és a septumok reticularis kötőszövetétől folyamatos bazális membrán választja el, de a keratinnegatív területek és a keratinpozitív hálózat határánál a bazális membrán szakadozottá válik. Ez az immunhisztokémiai lelet az első, amely magyarázhatja, hogy miért nincs a velőállományában vér-thymus barrier. A keratinnegatív terület és a septumok támasztószövetének azonossága azt sugallja, hogy a sövények és a keratinnegatív területek azonos eredetűek. A thymus tokja és sövényei a cranialis ganglionlécből származnak, ezért feltételezzük, hogy a keratinnegatív terület is ganglionléc-eredetű. A velőállomány vérerei a keratinnegatív területben helyezkednek el, ezért minden, a thymusból kilépő vagy abba belépő, immunológiailag kompetens sejtnek keresztül kell mennie a keratinnegatív területen. Ez azt sugallja, hogy a keratinnegatív terület a thymus tranzitzónája. A hematoxilin-eozin festés alapján megjelenő kéreg-velő határt nem reprezentálja sejtes háttér, de a keratinpozitív hálózat és a keratinnegatív terület között húzódó határt sejtes összetétele határozza meg (epithelium-mesenchyma). Feltételezzük, hogy a keratinnegatív terület és a keratinpozitív hálózat között lévő határ a thymus valódi szövettani és funkcionális határa. Orv Hetil. 2019; 160(5): 163–171.
The surface epithelium of the bursa of Fabricius consists of interfollicular (IFE) and follicle-associated epithelium (FAE). The IFE comprises (i) cylindrical-shaped secretory cells (SC) and (ii) cuboidal basal cells (BCs). The FAE provides histological and two-way functional connections between the bursal lumen and medulla of the follicle. We used a carbon solution and anti-caveolin-1 (Cav-1) to study the endocytic activity of FAE. Carbon particles entered the intercellular space of FAE, but the carbon particles were not internalized by the FAE cells. Cav-1 was not detectable in the FAE cells or the medulla of the bursal follicle. The absence of Cav-1 indicates that no caveolin-mediated endocytosis occurs in the FAE cells, B cells, bursal secretory dendritic cells (BSDC), or reticular epithelial cells. Surprisingly, a significant number of Cav-1 positive cells can be found among the SC, which are designated SC II. Cav-1 negative cell are called SC I, and they produce mucin for lubricating the bursal lumen and duct. Occasionally, BCs also express Cav-1, which suggests that BC is a precursor of a SC. Transmission electron microscopy confirmed the existence of type I and II SC. The SC II are highly polarized and have an extensive trans-Golgi network that is rich in different granules and vesicles. Western blot analysis of bursa lysates revealed a 21-23 kDa compound (caveolin) and Filipin fluorescence histochemistry provided evidence for intracellular cholesterol. High amount of cholesterol in the feces shows the cholesterol efflux from SC II. The presence of Cav-1 and cholesterol in SC II indicates, that the bursa is a complex organ in addition to possessing immunological function contributes to the cholesterol homeostasis in the chickens.
