Role of bursin in the development of B lymphocytes in chicken embryonic Bursa of Fabricius

In ovo feeding of probiotic lactobacilli differentially alters expression of genes involved in the development and immunological maturation of bursa of Fabricius in pre-hatched chicks

Compelling evidence indicates that immunological maturation of the gut-associated lymphoid tissues, including the bursa of Fabricius, is dependent upon antigenic stimulation post-hatch. In view of these data, the present study investigated the impact of exposing the immune system of chick embryos to antigenic stimuli, via in ovo delivery of poultry-specific lactobacilli, on the expression of genes associated with early bursal development and maturation. Broiler line embryonated eggs were inoculated with 106 and 107 colony-forming units (CFUs) of an individual or a mixture of Lactobacillus species, including L. crispatus (C25), L. animalis (P38), L. acidophilus (P42), and L. reuteri (P43), at embryonic day 18 (ED18). The bursa of Fabricius was collected from pre-hatched chicks (ED20) to measure the expression levels of various immune system genes. The results revealed that L. acidophilus and the mixture of Lactobacillus species at the dose of 106 CFU consistently elicited higher expression of genes responsible for B cell development, differentiation, and survival (B cell activating factor (BAFF), BAFF-receptor (BAFF-R)), and antibody production (interleukin (IL)-10) and diversification (TGF-β). Similar expression patterns were also noted in T helper (Th) cell-associated cytokine genes, including Th1-type cytokines (interferon (IFN)-γ and IL-12p40), Th2-type cytokines (IL-4 and IL-13) and Th17 cytokine (IL-17). Overall, these results suggest that the supplementation of poultry-specific lactobacilli to chick embryos might be beneficial for accelerating the development and immunological maturation of the bursa of Fabricius. However, further studies are required to determine if the changes in gene expression are associated with the developmental trajectory and phenotypes of bursal cells.

Transcriptome analysis revealed the roles of long non-coding RNA and mRNA in the bursa of Fabricius during pigeon (Columba livia) development

The bursa of Fabricius (BF) is the critical humoral immune organ to birds, playing an essential role in B lymphocyte differentiation. However, unlike other poultries, surgical removal of pigeon BF did not limit humoral immune responsiveness. To investigate the expression profiles and the potential role of mRNA and long non-coding RNA (LncRNA) in squab BFs, transcriptome analysis was performed by RNA-Sequencing (RNA-Seq) over three developmental stages (1-day, 13 and 26 days old). We identified 13,072 mRNAs and 19,129 lncRNAs, of which 2,752 mRNAs and 1,515 lncRNAs were differential expressed (DE) in pigeon BFs over three developmental stages. Cluster analysis presented different expression patterns in DE mRNAs and lncRNAs. Functional enrichment analysis revealed that DE lncRNAs and mRNAs with distinct expression patterns might play crucial roles in the immune system process and tissue morphogenesis. In particular, some DE genes and lncRNAs with higher expression levels in 13D or 26D are related to lymphocyte activation and differentiation, adaptive immune response, positive regulation of immune response, leukocyte migration, etc. Protein-protein interaction (PPI) network and Molecular Complex Detection (MCODE) analysis sreened six significant modules containing 37 genes from immune-related DE gene cluster, which is closely linked in B cell activation, lymphocyte differentiation, B cell receptor signaling pathway, etc. Our study characterizes mRNA and lncRNA transcriptomic variability in pigeon BFs over different developmental stages and enhances understanding of the mechanisms underlying physiological functions of pigeon BF.

Avian dendritic cells: Phenotype and ontogeny in lymphoid organs

Dendritic cells (DC) are critically important accessory cells in the innate and adaptive immune systems. Avian DCs were originally identified in primary and secondary lymphoid organs by their typical morphology, displaying long cell processes with cytoplasmic granules. Several subtypes are known. Bursal secretory dendritic cells (BSDC) are elongated cells which express vimentin intermediate filaments, MHC II molecules, macrophage colony-stimulating factor 1 receptor (CSF1R), and produce 74.3+ secretory granules. Avian follicular dendritic cells (FDC) highly resemble BSDC, express the CD83, 74.3 and CSF1R molecules, and present antigen in germinal centers. Thymic dendritic cells (TDC), which express 74.3 and CD83, are concentrated in thymic medulla while interdigitating DC are found in T cell-rich areas of secondary lymphoid organs. Avian Langerhans cells are a specialized 74.3-/MHC II+ cell population found in stratified squamous epithelium and are capable of differentiating into 74.3+ migratory DCs. During organogenesis hematopoietic precursors of DC colonize the developing lymphoid organ primordia prior to immigration of lymphoid precursor cells. This review summarizes our current understanding of the ontogeny, cytoarchitecture, and immunophenotype of avian DC, and offers an antibody panel for the in vitro and in vivo identification of these heterogeneous cell types.

Effects ofLactobacillus plantarumon production performance, immune characteristics, antioxidant status, and intestinal microflora of bursin-immunized broilers

Examples of probiotics that can promote host health by improving its intestinal microbial balance and intestinal immunity belong to the genus Lactobacillus. Bursin (BS) is a peptide isolated from the bursa of Fabricius for use as an adjuvant for a variety of immunogens. To investigate the synergistic effects of Lactobacillus plantarum (LP) dietary supplementation and BS immunization on production performance, immune characteristics, antioxidant status, and intestinal microflora in broilers, we randomly allocated 200 1-day-old broilers of mixed sex into 4 treatments in a 2 × 2 factorial arrangement (LP–/BS–, LP–/BS+, LP+/BS–, LP+/BS+) for 42 days. BS immunization enhanced immune response by increasing serum total immunoglobulin G concentration and interleukin-6 concentration, promoted antioxidant capacity by increasing catalase activities in serum and liver and by decreasing serum malondialdehyde (MDA) content at 42 days of age (DOA), and enriched intestinal microflora diversity. LP supplementation enhanced immune response by increasing interleukin-2 concentration at 42 DOA; promoted antioxidant capacity by increasing liver catalase activities, increasing glutathione peroxidase activities in serum and liver at 21 DOA, and decreasing serum MDA content at 42 DOA; promoted intestinal microflora composition by decreasing total aerobes and Escherichia coli counts at 21 DOA, by increasing total anaerobes count at 21 DOA, and by increasing Lactobacillus spp. and Bifidobacterium spp. counts at both 21 and 42 DOA. The interactions between BS and LP had a significant effect on daily body mass gain and feed conversion ratio in the starter period (1–21 DOA); on interleukin-2 concentration and liver MDA content at 21 DOA; and on thymus index, peripheral lymphocyte proliferation, and E. coli counts at 42 DOA. Overall, these data suggest that the combination of LP dietary supplementation and BS immunization promoted the production performance, immune characteristics, antioxidant status, and intestinal microflora of broilers.

New insight into the structure, development, functions and popular disorders of bursa Fabricii

Humoral immune responses in birds, contrary to mammals, depend on the normal functioning of bursa Fabricii. Recent studies have delivered new information about the structure, development and origin of cells that compose the bursa environment. Several viral infections affect bursa, causing lymphocyte depletion or excessive proliferation. This review summarizes data on the development and histology of healthy bursa and introduces some common disorders that affect this organ.

Expression patterns of the prolactin receptor gene in chicken lymphoid tissues during embryogenesis and posthatch period

Prolactin (PRL) is a pituitary hormone with multiple homeostatic roles among vertebrates. Although it has mainly been studied in relation to its role during the initiation and maintenance of incubation behavior in avian species, it has also been shown to act on the immune system. In this study, levels of PRL receptor (PRLR) mRNA were quantified by real-time PCR, and tissue expression was localized by in situ hybridization in primary and secondary lymphoid organs. Prolactin receptor was shown to be expressed in the bursa follicles, thymus lobules, and splenic pulp at all stages of development examined. Levels of PRLR expression were consistently higher in the bursa of Fabricius when compared with other lymphoid organs, suggesting that PRL acts primarily on bursal development. Furthermore, levels of PRLR mRNA appeared to fluctuate during embryogenesis, with a significant increase observed at embryonic day 19 in the bursa, at 7 d of age in the thymus, and on hatching day in the spleen. Thus, PRL might play an important role during the development of the immune system in chickens.

Effects of Anti-Bursin Monoclonal Antibody on Immunosuppression in the Duck (Cherry Valley Duck)

To study the immunologic function of bursin, we analyzed the effects of anti-bursin monoclonal antibody (mAb) on the immunosuppression in ducks (Cherry Valley duck) by injecting various doses of the anti-bursin mAb into 13-d duck embryos. After hatch, cell-mediated immune activity and humoral responses were studied using lymphocyte proliferation test, tube agglutination test, and indirect enzyme-linked immunosorbent assay to detect anti-Escherichia coli antibodies and antibodies to Riemerella anatipestifer, respectively. Simultaneously, relative weights (BW-adjusted) of bursa of Fabricius (BF), spleen, and thymus were determined. Additionally, the morphology of BF, spleen, and thymus was examined at various ages using conventional histology. Follicle morphology of BF was analyzed by image analysis. The results indicated that anti-bursin mAb markedly decreased duck lymphocyte proliferation, the antibody-producing ability to bacteria, as well as the relative BF weight. Moreover, the anti-bursin mAb hindered the development of BF follicles.

Histomoniasis in the Bursa of Fabricius of Chickens

Histomoniasis was diagnosed in a flock of 6-wk-old commercial chickens. Clinical signs included depression, stilted gait, inappetence, and a slight increase in mortality. At necropsy, there were pale-yellow to dark-gray circular and depressed necrotic lesions in the liver. The ceca were enlarged and impacted with caseous cores. Cecal worms were not observed either at necropsy or on histopathology. Histomonads were demonstrated microscopically within the bursa of Fabricius in addition to the liver, ceca, and spleen. This is the first report of the presence of histomonads in the bursa of Fabricius in commercial chickens.

Cell-mediated immunity in poultry

In avian species, adaptive immunity involves both humoral and cell-mediated immune (CMI) responses. Although humoral or antibody-mediated immune responses are particularly effective against extracellular antigens, CMI responses are specialized in the elimination of intracellular antigens; the latter include those that have entered cells via the endocytic pathway (exogenous antigens; e.g., phagocytosed bacteria) or were produced within the cell such as viral proteins and proteins resulting from neoplastic transformation of the cell (endogenous antigens). CMI responses, like most humoral immune responses, are tightly regulated and require "help" from T helper cells, specifically the type 1 T helper cells (Th1, hence, the name Th1 responses). Th1 cells are characterized by their production of cytokines such as interferon-gamma (IFN-gamma), tumor-necrosis factor-alpha (TNF-alpha), and interleukin-2 that drive CMI responses. The functional effectors of CMI responses are various immune cells including cytotoxic lymphocytes (cytotoxic T cells and natural killer cells) and macrophages. Cytotoxic lymphocytes and macrophages are specialized in the elimination of endogenous and exogenous antigens, respectively. In the past decade, substantial progress has been made in defining the role and regulation of avian CMI responses. Other advances have addressed strategies that strengthen this arm of adaptive immunity to optimize defense as well as protection against neoplastic diseases and nonneoplastic diseases caused by intracellular pathogens.

Chicken peripheral blood CD3+CD4-CD8- cells are regulated by endocrine and nerve systems

The existence of CD3(+)CD4(-)CD8(-) T cells in thymus and spleen has already been known. However, because of the presence of large amounts of thrombocytes in peripheral blood (PB), the proportion of CD3(+)CD4(-)CD8(-) T cells in PB has yet to be investigated. Therefore, the proportion of peripheral T cell-subsets was investigated in 6-week-old chickens. The percentage of CD3(+) cells, CD4(+) cells, CD8 alpha(+) cells, CD8 beta(+), and CD3(+)CD4(-)CD8(-) cells was 76%, 41%, 14%, 5%, and 15%, respectively. The proportion of CD3(+)CD4(-)CD8(-) cells in PB increased during egg-laying periods and in chickens treated with an analog of estrogen, while it decreased with age and in response to restraint stress. All of the CD3(+)CD4(-)CD8(-) cells expressed TCR1, and did not have NK activity. CD3(+)CD4(-)CD8(-) cells represent about 60% of peripheral TCR1(+) cells. These findings indicate that the proportion of CD3(+)CD4(-)CD8(-) cells is regulated by the endocrine and nerve systems.