No abstract

Intestinal epithelial cells are multi-tasked cells that participate in digestion and absorption as well as in protection of the digestive tract. While information on the physiology and immune functions of intestinal epithelial cells in mammals is abundant, little is known of their immune function in birds and other species. Our main objectives were to study the development of anti-bacterial innate immune functions in the rapidly developing gut of the pre- and post-hatch chick and to determine the functional diversity of epithelial cells. After establishing primary intestinal epithelial cell cultures, we demonstrated their capacity to uptake and process bacteria. The response to bacterial products, LPS and LTA, induced expression of pro-inflammatory cytokine genes (IL-6, IL-18) as well as the expression of the acute phase proteins avidin, lysozyme and the secretory component derived from the polymeric immunoglobulin receptor. These proteins were then localized in gut sections, and the goblet cell was shown to store avidin, lysozyme as well as secretory component. Lysozyme staining was also located in a novel rod-shaped intestinal cell, situated at different loci along the villus, thus deviating from the classical Paneth cell in the mammal, that is restricted to crypts. Thus, in the chicken, the intestinal epithelium, and particularly goblet cells, are committed to innate immune protection. The unique role of the goblet cell in chicken intestinal immunity, as well as the unique distribution of lysozyme-positive cells highlight alternative solutions of gut protection in the bird.

Due to increase in awareness of poultry welfare and concomitant legislation, it has become necessary to determine poultry's response to stress, with minimal harm and maximum reliability. Several methods to determine the response to physiological stress were developed throughout the years to identify stressors and to measure stress in poultry. The most commonly used are plasma corticosterone levels and peripheral blood heterophil/lymphocyte ratio (H/L ratio). However, the value of these responses to determine a state of stress has been questioned in several instances, as these parameters are increased during the process of bird handling and blood sampling irrespective of the general state of stress. Due to these limitations, it appears that the classic stress markers might be sub-optimal in evaluating stress in poultry, particularly those encountered in high-stress environments. Thus, there is a continuing need for stress indicators, preferably indicators that are quantitative, highly repeatable, not influenced by handling and sampling, determined in peripheral blood, represent an initial response to the stressor, and do not daily fluctuate. As the immune system has been shown to rapidly respond to stress, we assessed pro-inflammatory gene expression in peripheral blood cells as an indicator for stress. We initially show that while corticosterone plasma levels and the H/L ratio were responsive to handling and blood sampling, pro-inflammatory gene expression (lysozyme, IL-1β, IL-6, and HSP-70) was not. We then determined the expression of the same pro-inflammatory genes during acute stress (transit) in layer pullets (hen and turkey) and during chronic stress (different caging densities of layers utilizing 2, 3, and 4 hens/cage). While gene expression was significantly and highly elevated during transit, the effect of differing caging densities on gene expression was minimal; collectively, this might indicate that expression of pro-inflammatory genes is more responsive to acute stress than to chronic stressors. We propose to use pro-inflammatory gene expression in peripheral blood cells to measure responses to stress in poultry.

Induced molting ( IM ), a severe detriment to animal welfare, is still used in the poultry industry in some countries to increase or rejuvenate egg production and is responsible for several physiological perturbations, possibly including reactive oxidative stress, a form of metabolic stress. Because metabolic stress has been shown to induce a proinflammatory response involved in attempts to restore homeostasis, we hypothesized that similar responses followed IM. To confirm this hypothesis, we initially confirmed the establishment of oxidative stress during IM in 75-wk-old layers by demonstrating increased production of advanced glycation end products ( AGE ). Concomitant with increased oxidative metabolites, cellular stress was demonstrated in peripheral blood leukocytes ( PBL ) by increased levels of stress gene products (the glucocorticoid receptor, sirtuin-1, and heat shock protein 70 mRNA). Increased expression of stress proteins in PBL was followed by a proinflammatory response as demonstrated by increased levels of proinflammatory gene products (IL-6 and IL-1β mRNA); increased expression of these gene products was also demonstrated in direct response to AGE in vitro, thus establishing a direct link between oxidative and cellular stress. To establish a possible pathway for inducing a proinflammatory response by PBL, we showed that AGE increased a time dependent expression of galactin-3, Toll-like receptor-4, and nuclear factor - κB, all involved in the proinflammatory activation pathway. In vivo, AGE formed complexes with increased levels of circulating acute phase proteins (lysozyme and transferrin), products of a proinflammatory immune response, thereby demonstrating an effector response to cope with the consequences of oxidative stress. Thus, the harmful consequences of IM for animal welfare are extended here by demonstrating the activation of a resource-demanding proinflammatory response.

No abstract