Regulation of early chicken thymocyte proliferation by transforming growth factor-beta from thymic stromal cells and thymocytes

Effects of age on immune function in broiler chickens

BACKGROUND

There are many diseases in poultry, many of which are caused by poor immune function. It is not clear how cytokines and various immune cell functions change with age in modern broilers. The purpose of this study was to explore the patterns of development of the immunity of the broiler chickens in cage.

RESULTS

The results showed that there were 3 development patterns of immunity in the broiler chickens. The first pattern was Down-Up. Cytokines and some immune indicators first decreased and then increased, and the lowest levels of immunity basically occurred from d 6 to 13. The second pattern was Up-Down, and from d 30 to 34, the highest levels of non-specific cellular immunity components, such as the peripheral blood mononuclear macrophage ratio, specific cellular immunity components, such as the peripheral blood helper T (Th) cell ratio and T cell and B cell proliferation activity, and mucosal immunity components, such as the ileal CD4, TGF-β1 and IgA mRNA levels, were observed. The third pattern was Up-Up, and the levels of the non-specific cellular immunity components, such as the serum nitric oxide (NO), C3 and C4 levels, the specific cellular immunity components, such as the spleen index, peripheral blood IL-2, IFN-γ/IL-4, cytotoxic T (Tc) cell ratio, and splenic NF-κB mRNA levels, the humoral immunity components, such as the serum IgG level, the mucosal immunity components, such as the ileal MHC-II, CD3d, TCRβ subunit, TCRζ subunit, IFN-γ, pIgR mRNA and ileal mucosa sIgA levels, were continuing to increase from d 1 to 34.

CONCLUSIONS

It could be concluded that the immune system and its function have not developed well in the broiler chickens d 6 to 13 and that the immune system does not mature until d 30 to 34 in the broiler chickens in cages. It is necessary to enhance the immune function of the broiler chickens through nutritional measures from d 1 to 30.

Regulation of gene expression in chickens by heat stress

Abstract

High ambient temperatures are a critical challenge in the poultry industry which is a key producer of the animal-based food. To evaluate heat stress levels, various parameters have been used, including growth rates, blood metabolites, and hormones. The most recent advances have explored expression profiling of genes that may play vital roles under stress. A high ambient temperature adversely affects nutrient uptake and is known to modulate the expression of genes encoding for sodium-dependent glucose transporters, glucose transporters, excitatory amino acid transporters, and fatty acid-binding proteins which are responsible for the absorption of macronutrients in the intestine. Various defensive activities are stimulated to protect the cell of different tissues from the heat-generated stress, including expression of early stress response genes coding for heat shock protein (HSP), c-FOS like protein, brain-derived neurotrophic factor (BDNF), and neuronal nitric oxide synthase (nNOS); antioxidant enzyme genes such as superoxide dismutase (SOD), catalase (CAT), and nicotinamide adenine dinucleotide phosphate oxidase (NOX4); and immune-related genes such as cytokines and toll-like receptors (TLRs). The potential role of HSPs in protecting the cell from stress and their presence in several tissues make them suitable markers to be evaluated under heat stress. BDNF and c-FOS genes expressed in the hypothalamus help cells to adapt to an adverse environment. Heat causes damage to the cell by generating reactive oxygen species (ROS). The NOX4 gene is the inducer of ROS under heat stress, which is in turns controlled by antioxidant enzymes such as SOD and CAT. TLRs are responsible for protecting against pathogenic attacks arising from enhanced membrane permeability, and cytokines help in controlling the pathogen and maintaining homeostasis. Thus, the evaluation of nutrient transporters and defense mechanisms using the latest molecular biology tools has made it possible to shed light on the complex cellular mechanism of heat-stressed chickens. As the impacts of heat stress on the above-mentioned aspects are beyond the extent to which the reduced growth performance could be explained, heat stress has more specific effects on the regulation of these genes than previously thought.

Graphical abstract

Effect of heat exposure on the nutrient transporters, antioxidants, and immune inflammation in chickens. Most of the nutrient transporters were suppressed under heat stress. Increase in the production of reactive oxygen species resulted in enhanced production of antioxidant enzymes. Expression of various proinflammatory cytokines and toll-like receptors were enhanced due to heat stress in chicken.

Down-regulation of Treg cells and up-regulation of TH1/TH2 cytokine ratio were induced by polysaccharide from Radix Glycyrrhizae in H22 hepatocarcinoma bearing mice

Radix Glycyrrhizae polysaccharide (GP) possesses multiple pharmacological activities. However, the effect of GP on CD4+CD25+ regulatory T (Treg) cells has not been elucidated. This study aimed to investigate the effects of GP on Treg cells and Th1/Th2 cytokines in H22 hepatocarcinoma tumor-bearing mice. The results demonstrated that GP inhibits tumor progression. In the lymph nodes of the tumor microenvironment and spleen, the proportion of Treg cells was significantly higher in the tumor-bearing mice. GP administration down-regulated the population of Treg cells (P < 0.01) and decreased lymph node Foxp3 and IL-10 mRNA expression (P < 0.01). In addition, GP treatment decreased IL-10 and TGF-β level (P < 0.01) and increased IL-2 and IL-12p70 level in serum (P < 0.01). In conclusion, GP reduced the proportion of Treg cells and Foxp3 lowered expression in Treg cells, and up-regulated Th1/Th2 cytokine ratio in serum in the tumor bearing mice, which might partially cause the inhibition of tumor growth.

Carboxypeptidase E, an essential element of the regulated secretory pathway, is expressed and partially co-localized with chromogranin A in chicken thymus

Although the functions of hormones and neuropeptides in the thymus have been extensively studied, we still do not know whether these intra-thymic humoral elements are released in a stimulated manner via the regulated secretory pathway or in a constitutive manner. Carboxypeptidase E (CpE) and chromogranin A (CgA) are functional and structural hallmarks of the regulated secretory pathway in (neuro)endocrine cells. Whereas we have previously shown a CgA-positive neuroendocrine population in the chicken thymus, the current study assesses the expression of CpE in the thymus, both at the mRNA and the protein level. Our immunohistochemical studies provide evidence for the co-existence of CgA and CpE in identical neuroendocrine cells in the thymus. CpE and CgA dual-positive cells have primarily been found in the transition zone between the cortex and medulla of the thymus, an area known to contain numerous arterioles and to be innervated by the autonomic nervous system. Our findings suggest that the diffuse neuroendocrine system serves as a relay for nervous stimuli delivered by the sympathetic and/or parasympathetic nervous system. Thus, these newly defined neuroendocrine cells might play an important role in the immuno-neuro-endocrine cross-talk in the thymus, potentially enabling thymopoiesis to be fine-tuned via the regulated secretory pathway by a variety of physical and environmental factors.

Immunolocalization of TGF-beta2 in the rat thymus during late stages of prenatal development

The aim of this study was to investigate the immunolocalization of transforming growth factor beta (TGF-beta2) in rat thymic stromal cells and thymocytes and investigate the roles of TGF-beta2 in thymopoiesis during the late stages of fetal development. Twelve adult pregnant female Wistar rats weighing 250-270 g were used in this study. The rats were killed by cervical dislocation on gestation days 16 (GD16), 18 (GD18) and 20 (GD20). Fetal thymus glands were prepared and examined by an immunohistochemical technique to reveal binding of an anti-TGF-beta2 rabbit polyclonal antibody. The thymic primordium was surrounded with a connective tissue capsule at GD16 and at this stage TGF-beta2 immunoreactivity was not observed. At GD18, the connective tissue capsule had formed septa which subdivided the tissue into lobules and at this stage TGF-beta2 immunolocalization was detected in the capsule and in thymocytes. Lobulation was more evident at GD20 and TGF-beta2 immunoreactivity of thymocytes was more extensive than on GD18. Results indicate that TGF-beta2 may play an important role in the organization or development of thymocytes in the late stages of thymopoiesis.

TGF-beta signaling in T cells: roles in lymphoid and epithelial neoplasia

Transforming growth factor-beta (TGF-beta) plays an essential role in regulating the homeostasis of cells in the lymphoid lineage. TGF-beta signaling is not required for normal thymopoiesis, but is essential for regulating the expansion, activation, and effector function of the mature CD4+ and CD8+ T cells in the peripheral lymphoid organs and target tissues. Recent studies in both mice and humans have elucidated an important and complex role for TGF-beta in regulatory T-cell biology. Disruption of TGF-beta signaling in T cells impairs the maintenance of regulatory T cells, results in the expansion of activated effector T cells, and is associated with the production of cytokines that have major effects on cells in their environment. While autoimmunity and inflammation are the principal phenotypes associated with the abrogation of TGF-beta signaling in T cells in mice, emerging evidence now also directly links Smad-dependent TGF-beta signaling in T cells to the suppression of epithelial neoplasia. The TGF-beta receptor-activated Smad3 plays a critical role in mediating many of the inhibitory effects of TGF-beta signaling in T cells, and has now been established as an important suppressor of leukemogenesis. These studies are increasing our awareness of the many complex mechanisms through which TGF-beta signaling controls the pathogenesis of cancer.

Embryonic age influences the capacity for cytokine induction in chicken thymocytes

Thymocyte responses to functional activation are of relevance to the evaluation of the efficacy of in ovo immunotherapies and vaccines in chickens. In this study we have demonstrated differences in chicken thymocyte responses according to developmental age. RNA samples from stimulated and unstimulated chicken thymocytes were assayed for messenger RNA encoding the cytokines interleukin-1beta (IL-1beta), IL-2, interferon-alpha (IFN-alpha), IFN-beta, IFN-gamma and transforming growth factor-beta4 (TGF-beta4), and also components of the major histocompatibility complex (MHC), beta2-microglobulin (beta2M) and the MHC class I alpha-chain (MHC IA). At embryonic day 14 thymocytes were least responsive to functional activation and differences existed even between thymocyte populations at embryonic day 18 and day 1 post-hatch. The duration of proliferation in response to stimulation was found to increase with increasing embryonic age. Mitogen stimulation of embryonic day 18 and day 1 post-hatch thymocytes induced up-regulation of IFN-gamma, IL-1beta and TGF-beta transcripts, and down-regulation of IFN-alpha, IFN-beta and IL-2 transcripts, with a higher induction of IFN-gamma, IL-1beta and TGF-beta transcripts in more immature T-cell-receptor-negative (TCR-) than TCR+ (TCR1+, TCR2+, or TCR3+) subsets. In contrast, in the mouse and human, both mature and immature thymocytes respond to mitogen stimulation with up-regulation of IL-2. Thymocytes from embryonic day 14 chicks responded to mitogen with a short burst of unsustained proliferation, and transcriptional down-regulation of the cytokines IL-2, IL-1beta, IFN-alpha, IFN-beta and IFN-gamma. These results suggest that embryonic day 14 thymocytes are largely unresponsive to mitogen. Transcripts encoding TGF-beta and type I interferons (IFN-alpha and IFN-beta) were constitutively expressed at high levels in very early thymocytes at embryonic day 14. Thymocytes at embryonic days 14 and 18 and day 1 post-hatch responded to mitogen stimulation with up-regulation of MHC IA transcript. The pattern of beta2M transcription following mitogen stimulation was distinct from that of the globally up-regulated MHC IA transcript, with up-regulation of beta2M transcription observed at embryonic day 18 and day 1 post-hatch but not at embryonic day 14. In thymocyte subsets, up-regulation of beta2M transcription was found to be specific to the CD8+ TCR+ population. The balance of responses in the embryonic thymus suggests that at all stages thymocytes have a reduced capacity for activation in comparison to mature thymocyte populations.

Developmental immunotoxicity of lead: Impact on thymic function

BACKGROUND

Since the potential effects of early exposure to lead on thymic functions have not been fully characterized, in this study we evaluated the capacity of lead to alter thymic function in juvenile chickens following embryonic exposure.

METHODS

Cornell K strain White Leghorn chicken eggs were administered lead acetate (400 microg/egg) or sodium acetate (control) on embryonic development (E12) with and without thymulin supplementation. Ex vivo production of interferon-gamma (IFN-gamma)-like cytokine by thymocytes and a delayed-type hypersensitivity (DTH) reaction were measured in the juvenile. Additionally, the effects of in vitro exposure to lead on both thymocytes and thymic stromal cells (TSCs) were evaluated.

RESULTS

Following E12 exposure to lead, ex vivo production of IFN-gamma-like cytokine by juvenile-derived thymocytes decreased significantly compared to the control. The same effect was observed when thymocytes were directly exposed to lead in vitro and stimulated with thymic stromal supernatant. In contrast, when TSCs were exposed to lead in vitro, no change was seen in their functional capacity for promoting cytokine production. In ovo supplementation with thymulin partially reversed lead-induced DTH depression without any change in IFN-gamma-like cytokine production. Embryonic exposure to thymulin alone partially depressed the DTH response.

CONCLUSIONS

These results suggest that lead can directly influence thymocyte function in the absence of the thymic microenvironment. Since thymulin levels may influence lead-induced immunotoxicity, embryonic endocrine status may be an important consideration. Lead exposure appears to alter thymic functions directly; however, indirect effects via endocrine factors are not precluded.

Differential regulation of cytokine gene expression by avian heterophils during receptor-mediated phagocytosis of opsonized and nonopsonized Salmonella enteritidis

Internalization of pathogens by phagocytic cells triggers the innate immune response, which in turn regulates the acquired response. Phagocytes express a variety of receptors that are involved in recognition of pathogens, including (1) pattern recognition receptors (PRR), which recognize conserved motifs, (2) complement receptors (CR), which recognize complement-opsonized pathogens, and (3) Fc receptors (FcR), which recognize antibody-opsonized pathogens. Recognition of microbes is accompanied by the induction of multiple cell processes, including the production of proinflammatory and anti-inflammatory cytokines and chemokines. The objective of the present experiments was to use probes to known avian proinflammatory and anti-inflammatory cytokines and TaqMan technology to ascertain levels of cytokine gene expression in avian heterophils following receptor-mediated phagocytosis of either nonopsonized Salmonella enteritidis (SE), serum-opsonized SE, or IgG-opsonized SE. Expression of interleukin-6 (IL-6) and IL-8, considered in mammals as a proinflammatory chemokine, were upregulated following exposure to the nonopsonized or the opsonized SE. However, mRNA expression for IL-18 and interferon-gamma (IFN-gamma) was downregulated, and the expression of mRNA for the anti-inflammatory cytokine transforming growth factor-beta4 (TGF-beta 4) was upregulated. Interestingly, IL-1beta mRNA expression was significantly upregulated in heterophils that phagocytized either the nonopsonized SE via PRRs or IgG-opsonized SE via FcRs, whereas serum-opsonized SE phagocytized by CRs induced a downregulation of IL-1beta mRNA. These results suggest that signaling interactions initiated by receptor recognition of the microbe surface differentially regulate the induction of inflammatory cytokines in avian heterophils.

Cytokines of birds: conserved functions--a largely different look

Targeted disruptions of the mouse genes for cytokines, cytokine receptors, or components of cytokine signaling cascades convincingly revealed the important roles of these molecules in immunologic processes. Cytokines are used at present as drugs to fight chronic microbial infections and cancer in humans, and they are being evaluated as immune response modifiers to improve vaccines. Until recently, only a few avian cytokines have been characterized, and potential applications thus have remained limited to mammals. Classic approaches to identify cytokine genes in birds proved difficult because sequence conservation is generally low. As new technology and high throughput sequencing became available, this situation changed quickly. We review here recent work that led to the identification of genes for the avian homologs of interferon-alpha/beta (IFN-alpha/beta) and IFN-gamma, various interleukins (IL), and several chemokines. From the initial data on the biochemical properties of these molecules, a picture is emerging that shows that avian and mammalian cytokines may perform similar tasks, although their primary structures in most cases are remarkably different.