Purine metabolism and B-lymphocyte development in the chicken bursa of fabricius.

The activity of three enzymes involved in the salvage pathway of purine nucleosides--purine nucleoside phosphorylase (PNP), xanthine dehydrogenase (XDH), and hypoxanthine-guanine phosphoribosyl transferase (HGPRT)--was investigated in cellular fractions of the chicken bursa of Fabricius differentially enriched in epithelial cells or lymphocytes. Markedly increasing levels of PNP and XDH were observed along with the enrichment in epithelial cells together with a slight, though significant, decrease in HGPRT activity. By contrast, a dramatic fall in PNP and XDH activities was detected along with the enrichment in lymphocytes together with a slight, though significant, increase in HGPRT activity. This sharply different distribution of the three enzymes, all sharing hypoxanthine as a substrate, clearly indicates that lymphocytes preferentially channel hypoxanthine into the salvage and interconversion pathways, phosphorylating it to IMP, while epithelial cells rapidly catabolize such a purine base to uric acid. Moreover, epithelial cells, unlike lymphocytes, are able to retain high intracellular levels of both hypoxanthine and inosine. These results support the possibility that epithelial cells contribute to the normal development of bursal lymphocytes by supplying such actively proliferating cells with purine rings and at the same time by preventing them from accumulating potentially toxic high levels of purine nucleotides being able to rapidly eliminate excess hypoxanthine as uric acid from the bursa environment into the bloodstream.     

Cryptosporidiosis of the bursa of fabricius and trachea in broilers

Cryptosporidial parasitisation of the bursa of Fabricius and trachea is described in broilers. The response in both tissues was of epithelial hyperplasia and inflammatory cell infiltration. No clinical signs were reported.     

Dynamic control of B lymphocyte development in the bursa of fabricius

The chicken is a foundational model for immunology research and continues to be a valuable animal for insights into immune function. In particular, the bursa of Fabricius can provide a useful experimental model of the development of B lymphocytes. Furthermore, an understanding of avian immunity has direct practical application since chickens are a vital food source. Recent work has revealed some of the molecular interactions necessary to allow proper repertoire diversification in the bursa while enforcing quality control of the lymphocytes produced, ensuring that functional cells without self-reactive immunoglobulin receptors populate the peripheral immune organs. Our laboratory has focused on the function of chB6, a novel molecule capable of inducing rapid apoptosis in bursal B cells. Our recent work on chB6 will be presented and placed in the context of other recent studies of B cell development in the bursa.     

On the development of the lymphoid follicles of the bursa of fabricius

The structural features of the development of the bursa of Fabricius in white Leghom chick embryos are depicted at carefully timed intervals during embryogenesis, with emphasis on the sequence of events between the ninth and twelfth days of incubation. The direction and character of the migration of lymphoid cell precursors and granulocytes from the intravascular space to intraepithelial sites, where the formation of the primitive lymphoepithelial nodule takes place, is demonstrated. The mechanism of the mode of migration of these cells through the stromal epithelial interface is described and illustrated with electron micrographs and their role in the development of the primitive lymphoid follicles is described and discussed.     

T-dependent areas in the chicken bursa of fabricius: An immunohistological study

Background: The so-called diffusely infiltrated lymphoid tissue of the chicken bursa of Fabricius was previously described as a T-dependent bursal area. Methods: We have analyzed immunohistologically its postnatal development by using a battery of mAbs, most of them raised specifically to chicken T cells, in order to characterize phenotypically the nature of its cell components, appearance, development, and possible functional significance. Results: Our results demonstrate that this tissue represents poorly developed lymphoid aggregates, the cell content reminiscent of that found in other lymphoid tissues occurring throughout the avian gut. The first lymphoid elements appear in this bursal area only after hatchin, growing rapidly to reach the adult condition in the second week of postnatal life. They consist mainly of T lymphocytes, including principally CD4⁺ TcRαVβ1⁺ cells, which form cell groups and CD8⁺ cells, and TcRγδ⁺ lymphocytes, which predominate in the subepithelial area and within the epithelium. MHC Class II molecule-expressing cells and IgM-, IgG-, and IgA-positive B lymphocytes also occupy the subepithelial region. Conclusions: We propose that the bursal diffusely infiltrated lymphoid tissue of the chicken represents gut-associated lymphoid tissue involved in mounting immune responses to antigens that reach the bursal lumen via the cloaca. © 1995 Wiley-Liss, Inc.     

北京鸭法氏囊囊素的分离纯化

从2～3月龄北京鸭法氏囊得到的粗提物,经Se(?)hadex G-15和Molselect G-10两步分子筛层析后,得到了部分纯化的促PFC活性因子,该因子的分子量小于750dal。用高压液相色谱(HPLC)进一步分离活性组分,表明活性物质带有较多正电荷,极性较强。     

Follicle-associated epithelium and medullary epithelial tissue of the bursa of fabricius are two different compartments.

The bursae of Fabricius from the chicken and turkey were studied by light and electron microscopy and immunohistochemical methods. The study focused on the relationship of follicle-associated epithelium to the medulla. The follicle-associated epithelium was supported by 3 to 5 layers of stratified epithelial cells which were a continuation of the corticomedullary epithelial cells. The follicle-associated epithelium consisted of M cells and scattered secretory dendritic cells. The network of the reticular epithelial cells of the medulla was filled with secretory dendritic cells, B cells, and a few T cells and macrophages. The cellular content of the follicle-associated epithelium and the medulla suggested that they were different cellular compartments. Communication between the follicle associated epithelium and medullary epithelial compartment occurred through the supporting cells of the follicle-associated epithelium. When the supporting layers of the follicle-associated epithelium infolded into the medulla, they formed lamellated epithelial bodies similar to the thymic Hassall bodies. The lamellated bodies enclosed secretory dendritic cells but not lymphocytes. The infolding of supporting cells varied from follicle to follicle. The asynchronization of infolding contributed to heterogeneity of follicle composition. Follicle heterogeneity was demonstrated by differences in reactivity with a battery of monoclonal antibodies.     

Scanning electron microscopy of the bursa of fabricius from normal and testosterone-treated embryos

Scanning electron microscopy (SEM) has revealed the presence of projecting follicles (PF) and button-like follicles (BLF) in the bursa of Fabricius. This study was designed to examine the embryonic bursa with SEM to ascertain which type of follicle appears first and to compare the SEM of the bursa from normal embryos with those having received testosterone propionate (TP) on the 11th day of incubation. The bursa of the latter embryos exhibits an arrested lymphoid development. PF appeared in normal embryos by 16 days and were well developed by 18 days of embryonic development. Inter-follicular epithelium was apparent by 21 days of embryonic development in normal embryos. On the other hand, bursal follicles and interfollicular epithelium failed to form in TP birds. The TP-birds exhibited a characteristic pebble-like epithelium which may attest to the regressive influence of TP on bursal epithelium or to an arrested stage of epithelial development. The PF may lead to the development of BLF or the BLF may be derived independently of PF.     

Chicken B-cell-activating factor: regulator of B-cell survival in the bursa of fabricius

Previous studies on mammals have demonstrated that a tumour necrosis factor family member, B-cell-activating factor (BAFF) (BlyS, TALL-1), is mainly produced by myeloid and dendritic cells and that BAFF promotes B-cell differentiation and survival in a paracrine fashion. We have recently shown that BAFF is upregulated at the bursal stage of the avian B-cell development. We now show that the avian bursal B cells and B-cell lines, RP-9, RP-13 and DT40, express chicken BAFF (cBAFF). In situ hybridization confirms strong cBAFF expression within the bursal follicles. Like mammals, cBAFF is expressed in the avian myeloblast and myelomonocytic cell lines but not in the peripheral blood alphabeta and gammadelta T cells. The binding of recombinant human BAFF (hBAFF) to the bursal B-cells indicates a conserved receptor-ligand binding. Furthermore, the recombinant hBAFF has a positive effect on bursal cell proliferation and transiently inhibits cell death in vitro. In conclusion, cBAFF is highly conserved structurally, but as a novel observation we suggest cBAFF to function in an autocrine fashion to promote the growth and maturation of follicular B cells in bursa of Fabricius.     

北京鸭法氏囊中B细胞活性因子性质分析

从2～3月龄北京鸭法氏囊得到分子量小于10000道尔顿的提取物。该提取物能显著提高小鼠脾脏空斑形成细胞(简称PFC)的数目。它还具有对抗B细胞抑制剂环磷酰胺(简称CP)的作用:注射了CP的小鼠PFC数目明显下降,此时再注射囊提取物则能恢复小鼠产生PFC的能力;该提取物还能延长致死量CP处理后小鼠的存活期。表明法氏囊提取物中有些因子能够促进B细胞的发育成熟及其功能的正常发挥。把这种因子称为囊素(Bursatin)。经高温或蛋白水解酶处理,囊素的促PFC活性丧失,表明其很可能是肽类物质。囊提取物能提高小鼠脾细胞中cAMP含量,提示囊素可能以cAMP为介导而起作用。此外,囊提取物还有增多胸腺细胞中E-玫瑰花形成细胞数目的活性,表明提取物中可能有多种活性因子或某因子有多种活性。     

Dome epithelium and follicle-associated basal lamina pores in the avian bursa of fabricius

Background: The immunological role played by the avian bursa of Fabricius has been well established. Although numerous studies have also reported on the development and general morphology of this organ, some structure-function relationships still hae not been fully explained. Methods. Bursae from chickens at three developmental stages were removed and examined by scanning electron micropscopy. Routine preparation was used as well as sonication (Microdissection). Micrographs were used for qualitative morphological study and for quantitative morphometric analyses. Results: Routine SEM observations were similar to those previously reported in the literature. Sonicated specimens allowed topographical study of various levels of surface erosion. Two types of surface cells were observed: typical absorptive epithelium and follicle-associated epithelial (FAE) cells. Erosion of the dome surface epithelium revealed basal lamina pores n the region over the subepithelial lymphoid follicles. These pores were present at hatching. Morphometric analysis of dome and pore areas. Conclusions: Basal lamina pores may provide a communication route between the lympghoid follicles and the external environment via the FAE cells. Also, the close association between the FAE cells of the epithelial domes, the epithelial pores, the capillary complex of the previously described bursal-blood barrier, and the subepithelial lymphoid follicles could represent a morphological “pure complex” that matures early in posthatching development and may be related to the immunological function of the bursa. © 1995 Wiley-Liss, Inc.     

Anti-vimentin monocional antibody recognizes a cell with dendritic appearance in the chicken's bursa of fabricius

The bursa of Fabricius was studied by immunohistochemical method using anti-vimentin monoclonal antibody (clone 3B4). This monoclonal antibody indentified a vimentin positive cell in the medulla of the bursal follicle. During the first 2 weeks of life the vimentin positive cells located along the corticomedullary border and later became prominent in the medulla with the exception of a narrow zone adjacent to the corticomedullary border. After hatching the accumulation of vimentin-type intermediate filaments on one side of the nucleus endowed the vimentin positive cells with a polarized appearance. This “cap-like” vimentin positive area of the cytoplasm determined the position of the major cell process. Within the medulla the Ia positive secretory dendritic cells contained secretory granules in one of the cell processes. The distribution, shape, and polarized appearance of the vimentin positive cells were identical with that of the secretory dendritic cells. Therefore, the anti-vimentin monoclonal antibody proved to be useful for identification of the bursal secretory dendritic cells. During rapid bursal growth the number of secretory dendritic cells increased, possibly, by proliferation of vimentin negative secretory dendritic cell precursors located along the corticomedullary border.     

Apparent adoptive immune enhancement by bone marrow and bursa of fabricius cells from juvenile chickens

The occurrence of enhancer cells (EC) in the bone marrow and bursa of Fabricius of unprimed and mouse erythrocyte (MRBC) primed birds was investigated. EC are defined operationally as immunocompetent cells that are incapable of adoptive immunity in embryo hosts but able to enhance the immune responsiveness of newly-hatched chick recipients. Weak to moderate immune enhancement was observed in chick hosts grafted with bursal cells from unprimed or MRBC-primed donors whereas with bone marrow cell transfer the immune enhancement was weak with cells from unprimed donors but modest to strong with those from primed donors. Thus antigen priming of donors had little effect on the EC level of the bursa but appeared to increase that in the bone marrow. Moreover, the EC activity of bone marrow of primed donors was donorage dependent. Response profile studies revealed that the EC level of donor bone marrow was low the first 2–3 days after immunization and high by day six. The elevated EC level in the bone marrow of immunized donors is believed due to both recruitment of immigrant cells of extramedullary origin and clonal expansion of medullary immunocompetent cells.     

Effect of carrageenan on the histology of the bursa of fabricius and the humoral immune response to SalmonellaO antigen

Bursal secretory cells have been studied with light and electron microscope after prolonged carrageenan treatment. Intravenous injected carrageenan decreased the number of secretory cells as early as 4 days after the first carrageenan administration. Degranulation of the secretory cells may have made it difficult to identify these cells. The discharge of granules from the secretory cells was indicated by the appearance of a large amount of extracellular substance on the cell surface. The carrageenan may have accelerated the IgM-IgG switch after immunization with SalmonellaO antigen. The rapid IgM-IgG switch was preceded by degranulations of the secretory cells. Therefore, the secretory products of the cells might have contributed to the switch. The number of secretory cells in the carrageenan-treated birds increased by the secondary immunization. Many of these secretory cells were immature and located close to the corticomedullary border. The young cells revealed a large blastlike nucleus and bulky cytoplasm with granules surrounding the cytocentrum and Golgi zone.