Locally applied testosterone is a novel method to influence the development of the avian bursa of Fabricius

Characterization and ontogeny of a novel lymphoid follicle inducer cell during development of the bursa of Fabricius

The avian bursa of Fabricius (BF) is a primary lymphoid organ, where B-cell development occurs within bursal follicles of epithelial origin. During embryogenesis the epithelial anlage of the BF emerges as a diverticulum of the cloaca surrounded by undifferentiated tail bud mesenchyme. While it is believed that the epithelial-mesenchymal BF primordium provides a selective microenvironment for developing B cells, the initial events inducing lymphoid follicle formation are not fully elucidated. Using wild type and CSF1R-eGFP transgenic chick embryos, we find that separate B cell, macrophage and dendritic cell precursors enter the BF mesenchyme, migrate to the surface epithelium, and colonize the lymphoid follicle buds. Detailed immunocytochemical characterization revealed a novel EIV-E12+ blood-borne cell type, colonizing the surface epithelium of the BF rudiment before the entry of myeloid and lymphoid lineages and the appearance of this cell type coincides with the onset of follicle bud formation. Chick-duck chimeras and chick-quail tissue recombination experiments suggest that EIV-E12+ cells represent a transient lymphoid inducer cell population. They are not dendritic or B cells precursors, and they are capable of follicle bud induction in both dendritic cell- and B cell-depleted bursae.

Effects of maternal androgens and their metabolite etiocholanolone on prenatal development in birds

Offspring phenotypes can be affected by maternal testosterone and androstenedione (A4), which are considered a tool of mothers to adjust offspring to a fluctuating environment. Yet testosterone and A4 are very rapidly metabolized by developing avian embryos, suggesting that either the maternal testosterone and A4 have potent organizational effects on the embryos extremely early before being metabolized or it is the metabolites that evoke phenotypic variation in the offspring. One of the metabolites, etiocholanolone, increases substantially during early embryonic development and is a likely candidate for mediating maternal effects as it can promote erythropoiesis. To investigate and compare the effects of testosterone and A4 with the possible effects of etiocholanolone during prenatal embryonic development, we increased their levels in black-headed gull eggs (Larus ridibundus), and used sham-injected eggs as controls. This species usually has 3-egg clutches in which maternal androgen levels increase with the egg-laying sequence. We analysed embryonic heart rate, peri-hatching biometric traits, the ratio of white to red blood cells (W/R ratio) and bursa development. We found that testosterone and A4 treatment increased embryonic heart rate irrespective of egg-laying sequence and decreased bill length and W/R ratio, whereas etiocholanolone did not mimic these effects. Instead, etiocholanolone treatment decreased tarsus length and brain mass. Our finding that etiocholanolone does not mimic the effects induced by testosterone and A4 suggests that the embryonic metabolism of maternal testosterone and A4 can potentially diversify the function of these maternal androgens.

Effects of Acremonium terricola Culture on the Growth, Slaughter Yield, Immune Organ, Serum Biochemical Indexes, and Antioxidant Indexes of Geese

Acremonium terricola culture (ATC) is a new type of green feed additive, and its main components include cordycepin, adenosine, and ergosterol. In this study, the Hortobagy geese were used as the experimental animals to explore the effects of ATC addition to the basal diet. Seven hundred and twenty 1-day-old Hortobagy geese were randomly divided into four treatment groups, each with 180 geese divided into six pens equally. The four treatments included the control group and three experimental treatments. Half of the geese in each group were males and half were females. All geese were offered the same basal diet with ATC supplementation at 0, 3, 5, and 7 g/kg. The results showed that basal diet supplementation with 7 g/kg ATC reduced the feed conversion rate (FCR) of Hortobagy geese in a highly significant manner (p < 0.01). When the dosage of ATC was 3 g/kg, the breast muscle rate and leg muscle rate of female geese were significantly increased (p < 0.05). ATC supplementation in the basal diet had no significant effect on the immune organ index of Hortobagy geese (p > 0.05). Basal diet supplementation with 3 g/kg and 5 g/kg ATC significantly reduced the alanine aminotransferase (ALT) content in the serum of female geese, significantly increased the total antioxidant capacity (T-AOC) of the serum, and significantly reduced the malondialdehyde (MDA) content in the serum (p < 0.05). The addition of 5 g/kg and 7 g/kg ATC to the basal diet reduced the blood glucose (GLU) content in male geese in a highly significant manner (p < 0.01). A basal diet supplemented with 3 g/kg and 7 g/kg ATC significantly reduced the MDA content in geese breast muscles (p < 0.05). Basal diet supplementation with 3 g/kg ATC highly significantly improved the T-AOC of female geese breast muscles (p < 0.01). Basal diet supplementation with 5 g/kg ATC significantly improved the T-AOC of female geese leg muscles (p < 0.01). In summary, basal diet supplementation with ATC enhances the growth performance and antioxidant properties of Hortobagy geese.

Development of innate immunity in chicken embryos and newly hatched chicks: a disease control perspective

Newly hatched chickens are confronted by a wide array of pathogenic microbes because their adaptive immune defences have limited capabilities to control these pathogens. In such circumstances, and within this age group, innate responses provide a degree of protection. Moreover, as the adaptive immune system is relatively naïve to foreign antigens, synergy with innate defences is critical. This review presents knowledge on the ontogeny of innate immunity in chickens pre-hatch and early post-hatch and provides insights into possible interventions to modulate innate responses early in the life of the bird. As in other vertebrate species, the chicken innate immune system which include cellular mediators, cytokine and chemokine repertoires and molecules involved in antigen detection, develop early in life. Comparison of innate immune systems in newly hatched chickens and mature birds has revealed differences in magnitude and quality, but responses in younger chickens can be boosted using innate immune system modulators. Functional expression of pattern recognition receptors and several defence molecules by innate immune system cells of embryos and newly hatched chicks suggests that innate responses can be modulated at this stage of development to combat pathogens. Improved understanding of innate immune system ontogeny and functionality in chickens is critical for the implementation of sound and safe interventions to provide long-term protection against pathogens. Next-generation tools for studying genetic and epigenetic regulation of genes, functional metagenomics and gene knockouts can be used in the future to explore and dissect the contributions of signalling pathways of innate immunity and to devise more efficacious disease control strategies.

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.