Chicken B-Cell-Activating Factor: Regulator of B-Cell Survival in the Bursa of Fabricius

Effects of Sihuang Zhili Granules on the Diarrhea Symptoms, Immunity, and Antioxidant Capacity of Poultry Challenged with Lipopolysaccharide (LPS)

A growing interest has been focused on Chinese herbs as alternatives to antimicrobial growth promoters, which are characterized by non-toxic side effects and drug resistance. The purpose of this study was to evaluate the effects of the Sihuang Zhili granule (abbreviated as Sihuang) on diarrhea, immunity, and antioxidation in poultry. Thirty male Leghorn chickens, aged 21 days, were randomly assigned to one of three groups with ten animals each. The control group (CON) received intraperitoneal saline injections, while the LPS-challenged group (LPS) and Sihuang intervention group (SH) received intraperitoneal injections of LPS (0.5 mg/kg of BW) and Sihuang (5 g/kg) at d 31, d 33, d 35, respectively. The control and LPS groups were fed a basal diet, while the SH group was fed a diet supplemented with Sihuang from d 21 to d 35. Analysis of the diarrhea index showed that the addition of Sihuang inhibited the increase in the diarrhea grade and the fecal water content caused by LPS, effectively alleviating poultry diarrhea symptoms. The results of the immune and antioxidant indexes showed that Sihuang significantly reduced the contents of the pro-inflammatory factors TNF- α and IL-1 β, as well as the oxidative stress markers ROS and MDA. Conversely, it increased the contents of the anti-inflammatory factors IL-4 and IL-10, along with the activities of antioxidant enzymes GSH-Px and CAT, thereby enhancing the immune and antioxidant abilities of chickens. Furthermore, Sihuang protected the chicken's ileum, liver, and immune organs from LPS invasion and maintained their normal development. In conclusion, this study confirmed the antidiarrheal effect of Sihuang in poultry farming and demonstrated its ability to improve poultry immunity and antioxidant capacity by modulating antioxidant enzyme activity and inflammatory cytokine levels.

Infection of bursal disease virus abrogates the extracellular glycoprotein in the follicular medulla

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.

Regulation and function of macrophage colony-stimulating factor (CSF1) in the chicken immune system

Macrophage colony-stimulating factor (CSF1) is an essential growth factor to control the proliferation, differentiation and survival of cells of the macrophage lineage in vertebrates. We have previously produced a recombinant chicken CSF1-Fc fusion protein and administrated it to birds which produced a substantial expansion of tissue macrophage populations. To further study the biology of CSF1 in the chicken, here we generated anti-chicken CSF1 antibodies (ROS-AV181 and 183) using CSF1-Fc as an immunogen. The specific binding of each monoclonal antibody was confirmed by ELISA, Western blotting and immunohistochemistry on tissue sections. Using the anti-CSF1 antibodies, we show that chicken bone marrow derived macrophages (BMDM) express CSF1 on their surface, and that the level appears to be regulated further by exogenous CSF1. By capture ELISA circulating CSF1 levels increased transiently in both layer and broiler embryos around the day of hatch. The levels of CSF1 in broilers was higher than in layers during the first week after hatch. Antibody ROS-AV183 was able to block CSF1 biological activity in vitro and treatment of hatchlings using this neutralising antibody in vivo impacted on some tissue macrophage populations, but not blood monocytes. After anti-CSF1 treatment, CSF1R-transgene reporter expressing cells were reduced in the bursa of Fabricius and cecal tonsil and TIM4⁺ Kupffer cells in the liver were almost completely ablated. Anti-CSF1 treatment also produced a reduction in overall bone density, trabecular volume and TRAP⁺ osteoclasts. Our novel neutralising antibody provides a new tool to study the roles of CSF1 in birds.

Changes in bursal B cells in chicken during embryonic development and early life after hatching

The bursa of Fabricius, the primary lymphoid organ for B cell development found only in birds, offers novel approaches to study B cell differentiation at various developmental stages. Here, we explored the changes and mechanism involved in the developmental stages of bursal B cells. The bursal B cells rapidly increased in the late embryonic stage and around hatching, which coincided with changes in specific cell surface markers. Moreover, the cells in the bursa were divided by size into small (low forward- and side-scatter) or large (high forward- and side-scatter) via flow cytometry. It is intriguing that the proportion of small and large B cells was reversed during this period. Because little is known about this phenomenon, we hypothesized that size-based B cell population could be used as an indicator to distinguish their status and stage during B cell development in chicken. The results demonstrated that large B cells are actively proliferating cells than small B cells. Additionally, large B cells showed higher mRNA expression of both proliferation- and differentiation-associated genes compared to small B cells. Taken together, these data show that large bursal B cells are the main source of proliferation and differentiation during B cell development in chickens.

Molecular cloning, genomic organization and expression analysis of the gene encoding bovine (Bos taurus) B-cell activating factor belonging to the TNF family (BAFF)

A novel bovine cDNA has been isolated by EST assembly and subsequently confirmed by using RT-PCR and designated bovine B-cell activating factor belonging to TNF family (bBAFF). The open reading frame (ORF) of this cDNA covers 843 bp, encoding 280 amino acids. The functional soluble part of bBAFF (bsBAFF) shows 96% and 91% identity with its pig and human counterparts, respectively, at the level of the primary protein structure. The bBAFF genomic sequence consists of six exons and five introns, is approximately 30 kb in size, and maps to bovine chromosome 12q. Southern blotting analysis indicated that the bBAFF gene is a single copy gene. Real-time quantitative PCR (qPCR) analysis revealed that bBAFF is predominantly expressed in bovine lymphoid tissues PBLs and spleen. The predicted three dimensional (3D) structure of the bsBAFF monomer analyzed by "comparative protein modeling" revealed that it is very similar to its human counterpart. In western blotting analysis, His6-tagged bsBAFF protein expressed in E. coli could be recognized not only by an anti-His6.tag mAb but also by an anti-human sBAFF mAb, indicating immunological cross-reactivity occurs between bovine and human sBAFF protein.

The BLyS family: toward a molecular understanding of B cell homeostasis

The B Lymphocyte Stimulator (BLyS) family of ligands and receptors regulates humoral immunity by controlling B lymphocyte survival and differentiation. Herein, we review the ligands and receptors of this family, their biological functions, and the biochemical processes through which they operate. Pre-immune B lymphocytes rely on BLyS signaling for their survival, whereas antigen experienced B lymphocytes generally interact more avidly with a homologous cytokine, A Proliferation Inducing Ligand (APRIL). The molecular basis for signaling via the three BLyS family receptors reveals complex interplay with other B lymphocyte signaling systems, affording the integration of selective and homeostatic processes. As our understanding of this system advances, molecular targets for manipulating humoral immunity in both health and disease should be revealed.

Oligodeoxynucleotides containing CpG motifs (CpG-ODN) predominantly induce Th1-type immune response in neonatal chicks

Earlier, we demonstrated that intramuscular administration of oligodeoxynucleotides containing CpG motifs (CpG-ODN) induces protection in neonatal chicks against a lethal challenge of Escherichia coli. However, the mechanism of induction of the protection was not clear. In an attempt to elucidate the mechanism of induced protection, we determined the kinetics of expression of cytokines/chemokines in the spleen and bursa of Fabricius of newly hatched chicks that had received intramuscular administration of CpG-ODN or non-CpG ODN compared to saline-treated controls. SyBr green, real-time quantitative reverse transcription polymerase chain reaction (RT-PCR) analysis of the RNA demonstrated increased expression of IL-1beta, IL-6, IL-8, IL-10, IL-18, IFN-gamma and MIP-3alpha mRNAs in the spleen and; IL-10 and IFN-alpha in bursa of Fabricious of chicks that had received CpG-ODN. However, non-CpG ODN failed to induce any of the cytokine. The increased level of IL-18 and IFN-gamma but not IL-4 mRNA suggests that the administration of CpG-ODN elicits a Th1 biased immune response, which may be important in inducing protection against infections in neonatal chicks. To our knowledge, this is the first report evaluating the induction of cytokines/chemokines in neonatal chicks following administration of CpG-ODN.

The BAFF-Interacting receptors of chickens

The TNF superfamily cytokine BAFF has crucial roles in homoeostatic regulation of B cell populations in mammals. Similar effects on peripheral B cells have been reported for chicken as for mammalian BAFF. Unlike mammalian BAFF, chicken BAFF is produced by B cells, implying an autocrine loop and consequent differences in regulation of B cell homoeostasis. Understanding of these mechanisms requires investigation of BAFF-binding receptors in chickens. We identified and characterised chicken receptors BAFFR and TACI, but found that the gene encoding the third BAFF-binding receptor, BCMA, was disrupted, implying differences in mechanisms for maintenance of long-lived antibody responses. A BAFFR-Ig fusion protein expressed in vivo lowered B cell numbers, showing that it was functional under physiological conditions. We found changes in the ratio of BAFFR and TACI mRNAs in the bursa after hatch that may account for the altered requirements for B cell survival at this stage of development.

Avian model for B-cell immunology--new genomes and phylotranscriptomics

The purpose of this review is to discuss the use of chicken and other model organisms in the study of B-cell development and function as well as to highlight the opportunities afforded by the expanded genome-sequencing efforts. A brief introduction on chicken B-cell biology is followed by discussion of somatic cell reverse genetic approaches using the DT40 cell line. The unique advantages of the DT40 system are emphasized with discussion on B-cell receptor signalling research as well as on DNA repair and mechanisms of immunoglobulin diversification. An attempt is made to compare and contrast the results from chicken with mouse knockouts on the one hand and RNAi with human cell lines on the other. Chicken is also emerging strongly as a platform for gene expression analysis, and avian studies are compared with mammalian studies. Multi-species gene co-expression analysis, which could also be termed phylotranscriptomics, aims to use the evolutionary distance between organisms to its advantage. This approach, still in its infancy, is also reviewed and its applicability to the chicken is discussed.

Two related ligands of the TNF family, BAFF and APRIL, in rabbit: Molecular cloning, 3D modeling, and tissue distribution

B-cell activating factor belonging to the TNF family (BAFF) and a proliferation-inducing ligand (APRIL) are two related members of the TNF ligand superfamily. These two ligands and their receptors, also termed "the BAFF/APRIL system", play important immunological roles, especially in the B-cell arm of the immune system. This paper reports the cloning and expression analysis of these two cytokines in rabbit (Oryctolagus cuniculus) by homology cloning. The complete transcript of the rabbit BAFF was sequenced and contained 1457 bp, including an 873 bp open reading frame. The predicted protein of 290 aa revealed the presence of the BAFF family signature, the "Flap". The soluble mature part of rabbit BAFF (sBAFF) showed 75-92% sequence identity with mammalian and avian homologs. The full-length cDNA of rabbit APRIL contained 1030 bp of which 753 bp are the open reading frame. The conserved potential N-glycosylation site and the cysteine residues were found in both the two ligands. The predicted three dimensional (3D) structures of sBAFF and sAPRIL analyzed by comparative protein modeling reveal that they are very similar to the human counterparts. Real-time PCR analysis revealed that rabbit BAFF gene was predominantly expressed in the lymphoid tissues, such as spleen and thymus; while the APRIL mRNA was found to be relatively high in a wide range of tissues. These findings indicate that BAFF and APRIL in rabbit play similar roles as in human. It provides the basis for investigation on their roles in regulating B-cell development and immune responses in rabbit and also contributes to our understanding of the evolution of these two novel TNF ligands.

The avian immune genome – a glass half-full or half-empty?

Although in broad terms the avian immune response is remarkably similar to that of mammals, when one looks at specifics birds have a different repertoire of immune organs, cells and molecules compared to those characterized in mammals. Birds lack organized lymph nodes, yet have the Bursa of Fabricius. Birds lack neutrophils and functional eosinophils, yet have a distinct group of polymorphonuclear granulocytes known as heterophils. Birds also have a different repertoire of cytokines, chemokines, Toll-like receptors, defensins and integrins, as detailed in this review.

Molecular cloning, in vitro expression and bioactivity of goose B-cell activating factor

B-cell activating factor (BAFF), belonging to the TNF family, is critical for B cell survival and maturation. cDNA of goose BAFF (gBAFF) was amplified from goose spleen by RT-PCR. The open reading frame (ORF) of gBAFF encodes a protein of 288-amino acid. The gBAFF shows 98, 92, 44 and 55% amino acid sequence identity with duck (dBAFF), chicken (cBAFF), mouse (mBAFF) and human BAFF (hBAFF), respectively. RT-PCR results showed that gBAFF mRNA is expressed in thymus and more highly expressed in the bursa of Fabricius and spleen. Recombinant soluble gBAFF (gsBAFF) expressed in Escherichia coli has molecular weight of approximately 19kDa. In vitro, purified gsBAFF was able to promote bursa B cells survival/proliferation in goose, duck and chicken. Furthermore, recombinant dsBAFF and csBAFF have a positive effect on goose, duck and chicken bursa B cells survival/proliferation. These findings indicate that gBAFF plays an important role in the survival/proliferation of goose B cells and, owing to its high evolutionary conservation, functional cross-reactivity exists between chicken, duck and goose BAFF.

Cloning, expression and bioactivity of duck BAFF

B cell activating factor (BAFF) belonging to the TNF family is critical for B cell survival and maturation. In the present study, we identified a duck BAFF cDNA, named dBAFF, by RT-PCR and RACE strategies. The open reading frame (ORF) of this cDNA encodes a 288-amino acid protein containing a predicted transmembrane domain and a putative furin protease cleavage site like chicken BAFF (cBAFF), human BAFF (hBAFF) and mouse BAFF (mBAFF). The amino acid identity between biologically soluble dBAFF and cBAFF, hBAFF or mBAFF is 97, 78 and 71%, respectively. RT-PCR analysis showed the dBAFF gene is strongly expressed in the bursa of fabricius. Recombinant soluble dBAFF (dsBAFF) fused with NusA.tag was efficiently produced in Origami B (DE3) pLysS expression host strain. In vitro, purified dsBAFF was not only able to promote survival of bursa B cells, but also able to co-stimulate proliferation of mammalian B cells with anti-IgM. Furthermore, recombinant hsBAFF has a positive effect on duck bursa B cells survival. These findings indicate dBAFF plays an important role in survival and proliferation of duck B cells and because of its high conservation in the evolution, functional cross-reactivity exists between mammalian and duck BAFF.

Ligand-independent signaling during early avian B cell development

Surface immunoglobulin (sIg) expression has been conserved as a critical checkpoint in B lymphocyte development. In the chicken embryo, only sIg+ B cells are selectively expanded in the bursa of Fabricius, a primary lymphoid organ unique to the avian species. We have previously demonstrated that an interaction between the antigen- binding sites of sIg and a specific bursal ligand(s) is not required to regulate this developmental checkpoint. Rather, the requirement for sIg expression can be attributed to the surface expression of the Igalpha/beta heterodimer associated with sIg. More specifically, ligand-independent signaling downstream of the Igalpha cytoplasmic domain drives all bursal stages of B cell development during embryogenesis. We discuss here a site-directed mutagenesis approach to identify the critical membrane proximal events involved in ligand-independent signaling during B cell development.

Transcriptional profiling reveals a possible role for the timing of the inflammatory response in determining susceptibility to a viral infection

Using a novel cDNA microarray prepared from sources of actively responding immune system cells, we have investigated the changes in gene expression in the target tissue during the early stages of infection of neonatal chickens with infectious bursal disease virus. Infections of two lines of chickens previously documented as genetically resistant and sensitive to infection were compared in order to ascertain early differences in the response to infection that might provide clues to the mechanism of differential genetic resistance. In addition to major changes that could be explained by previously described changes in infected tissue, some differences in gene expression on infection, and differences between the two chicken lines, were observed that led to a model for resistance in which a more rapid inflammatory response and more-extensive p53-related induction of apoptosis in the target B cells might limit viral replication and consequent pathology. Ironically, the effect in the asymptomatic neonatal infection is that more-severe B-cell depletion is seen in the more genetically resistant chicken. Changes of expression of many chicken genes of unknown function, indicating possible roles in the response to infection, may aid in the functional annotation of these genes.

Diversified bursal medullary B cells survive and expand independently after depletion following neonatal infectious bursal disease virus infection

The primary immunoglobulin repertoire of chickens is generated not by gene rearrangement but by a subsequent process of gene conversion in proliferating immature B cells within the follicles of a specialized gut-associated lymphoid organ, the bursa of Fabricius. Neonatal infection with infectious bursal disease virus can eliminate almost the entire bursal B-cell compartment. Thereafter, two types of follicle reappear. Larger follicles, with rapidly proliferating B cells and normal structure, are correlated with partial recovery of antibody response. Smaller follicles, lacking distinct cortex and medulla, appear unable to produce antigen-responsive B cells. To understand the genesis of the two types of follicle, we analysed their VL sequences and activation-induced deaminase mRNA levels. The results provide a model of bursal repopulation in which surviving bursal stem cells generate new follicles with normal morphology and function, while surviving medullary B cells continue to proliferate slowly, under the influence of stromal cells, giving rise to the smaller follicles. The latter remain fixed in a stage of development incapable of further gene diversification.

In ovo vitelline duct ligation results in transient changes of bursal microenvironments

The avian bursa of Fabricius has a direct connection to the cloaca via the bursal duct. Using the bursal duct ligation technique, it has been clearly shown that the B cells of the bursal follicles develop under the influence of cloacal antigens. These antigens have been suggested to be present on the bursal secretory dendritic cells in immunoglobulin G (IgG)-containing complexes. We studied the effect of maternal (yolk) antigens on the early development of B cells and the appearance of IgG-containing complexes of the bursal dendritic cells with a novel embryo manipulation technique, in ovo vitelline duct ligation. This operation blocked the direct (intestinal) transport of yolk substances into the intestine, but left the vitelline circulation intact. Vitelline duct ligation performed on embryonic day 17 resulted in serious but transient bursal underdevelopment during the first week of life: (1) IgG and the follicular dendritic cell marker 74.3 were not detectable on the bursal secretory dendritic cells, in spite of a normal serum IgG level and free communication with the cloacal lumen; (2) the number of B cells in the follicles was greatly reduced and they showed an altered phenotype, resembling that of the prebursal B cells. The intracloacal administration of different proteins effectively restored the bursal phenotype. These data suggest that maternal antigens indirectly help the maturation of bursal secretory dendritic cells and concomitantly that of B cells during the first week of life.