Novel model for chronic intestinal inflammation in chickens: (2) immunologic mechanism behind the inflammatory response

Authors: DAL POINT, GABRIELA - Texas A&M University; LEE, ANNAH - Texas A&M University; BORTOLUZZI, CRISTIANO - Texas A&M University; FARNELL, YUHUA - Texas A&M University; GOUGOULIAS, CHRISTOS - Innovad Nv/sa; Kogut, Michael - Mike

Submitted to: Developmental and Comparative Immunology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/25/2022
Publication Date: 9/5/2022
Citation: Dal Point, G.C., Lee, A., Bortoluzzi, C., Farnell, Y., Gougoulias, C., Kogut, M.H. 2022. Novel model for chronic intestinal inflammation in chickens: (2) immunologic mechanism behind the inflammatory response. Developmental and Comparative Immunology. 138. Article 104524. https://doi.org/10.1016/j.dci.2022.104524.
DOI: https://doi.org/10.1016/j.dci.2022.104524

Interpretive Summary: Until recently, poultry producers have relied on antibiotics to ensure bird health and production efficiency. However, with the removal of growth-promoting antimicrobials in poultry feed as the result of societal and regulatory pressures, intestinal inflammation has become more of an issue worldwide. For the poultry producer, chronic low-grade intestinal inflammation has a negative impact on the productivity of the poultry operation by impairing the ability of the birds to absorb nutrients and reach 100% of their growth and genetic potential. Although chronic intestinal inflammation can be induced by several environmental factors, diet is the main cause since some feed ingredients, such as soybean meal, are potent stimulators of the intestinal immune response. Research into understanding and regulating intestinal inflammation in poultry has been limited by the lack of a dependable in vivo model. This research has characterized a model of chronic inflammation in young chicks. By feeding the chicks a diet that is hard for their guts to digest, larger feed materials cause the immune cells in their guts to overact to them. In doing so, the cells produce substances, called cytokines, that constantly stimulate the gut immune system, resulting in chronic inflammation. This inflammation makes the chicks more susceptible to infections by disease causing germs. Hopefully, by identifying the cause of the inflammation, interventions that will reduce cytokine production can be given to the young chicks while still allowing them to grow and prosper, further reducing the prevalence of the disease-causing germs. This is important information for growers, the feed industry, and customers; the work contributes significantly to ongoing research efforts focused on increasing poultry production efficiency.

Technical Abstract: Intestinal inflammation in poultry is a complex response that involves immune and intestinal cells which is still not fully understood. Thus, to better understand the mechanisms that drive the chronic intestinal inflammation in fowl, we conducted an experiment applying a previously established nutritional model of low-grade chronic intestinal inflammation to evaluate cytokine and chemokine profiles in the chicken intestine. For this, we placed 90 one-day chickens into two treatments: (1) a control group (CNT) fed a corn-soybean diet and (2) a group fed a diet high in non-starch polysaccharides (NSP). At days 14, 22, 28, and 36 of age, 6 birds from each treatment were euthanized, and jejunal and ileal samples were collected for histological examination and cytokine measurements. The cytokines interferon-alpha (IFN-alpha), IFN-gamma, interleukin-16 (IL-16), IL-10, IL-21, IL-6, macrophage-colony stimulating factor (M-CSF), macrophage inflammatory protein 3alpha (MIP-3alpha), MIP-1beta, vascular endothelial growth factor (VEGF) and regulated upon activation, normal T cell expressed and presumably secreted (RANTES) were quantified in the intestinal tissue. Histologically, both jejunum and ileum of broilers fed NSP diet showed marked infiltration of mononuclear immune cells into the villi. Furthermore, these birds exhibited a significant (P<0.05) increase in MIP-3alpha concentration in the jejunum at 14d, but a dramatic reduction of M-CSF at 14 and 21d. Later at 28d and 36d, birds fed the NSP diet exhibited increased IL-16 concentration in the jejunum. Since M-CSF is a monocyte stimulatory cytokine and MIP-3alpha a chemokine primarily of T-cells, the reduced M-CSF and increased production of MIP-3alpha indicates a shift from an innate to adaptive immune response, specifically driven by T-cells, occurring around the third week of age in the NSP model. Lastly, as a result of the mononuclear cell infiltration and activation of T-cells, IL-16, a pro-inflammatory T-cell activating cytokine, increased. Therefore, the current work demonstrates the importance of adaptive immune cells, especially T-cells, that regulate chronic intestinal inflammation in broiler chicken. The current work is the first to measure chicken cytokine protein concentrations directly in the intestinal tissue and demonstrates the transition from a traditional innate immune response to a T-cell-mediated chronic inflammatory response.