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Title: Crop Immune Response Post-Salmonella Enteritidis Challenge in Eight Commercial Egg-Layer Strains and Specific Pathogen Free White Leghorn Chickens

item Vaughn, Lara
item Holt, Peter
item Moore, Randle
item Gast, Richard

Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/23/2007
Publication Date: 10/23/2007
Citation: Vaughn, L.E., Holt, P.S., Moore, R.W., Gast, R.K., Anderson, K.E. 2008. Crop Immune Response Post-Salmonella Enteritidis Challenge in Eight Commercial Egg-Layer Strains and Specific Pathogen Free White Leghorn Chickens. Avian Disease. 52:79-87.

Interpretive Summary: Our laboratory has been studying the development of immunity in the chicken gastrointestinal (GI) tract against Salmonella enteritidis (SE) to determine possible ways of increasing the resistance of the birds against this organism. SE remains an important food-poisoning pathogen because of its ability to enter the egg and infect humans when they consume the contaminated egg. We found that our laboratory specific-pathogen free (SPF) hens develop a strong immune response in the crop, a sort of pre-stomach used by the hen to store food when the stomach is full, following infection with SE. As pathogens such as SE must transit the crop in order to reach the intestine and cause infection, this could be an important organ to increase immunity against SE and possibly prevent gut infection and we wanted to see if similar immunity would be observed in commercial breeds of chicken. We infected 5 white-egg breeds and 3 brown-egg breeds of commercial laying hens with SE and followed the infection in the crop as well as the development of immunity and establishment of lymphoid tissues in this organ over time post infection. While some differences in breeds were observed with regards to length of infection and the intensity of the immune response, the crops in all breeds of laying chickens examined could be infected by SE, they all developed an immune response as well as showing increases in the amount of lymphoid tissue found within the organ. These results show that immunity in the crop against SE is not unique to the SPF hen but rather occurs in a broad range of layer breeds and the crop could therefore be a good site for inducing an immune response to protect against gut infection.

Technical Abstract: We investigated the crop immune response against Salmonella Enteritidis (SE)-challenge in eight commercial egg-layer strains (5 white-egg layer & 3 brown-egg layer) and specific pathogen free (SPF) White Leghorn (WL) hens. Pre- and post-SE-challenge mucosal immune responses within the crops were evaluated. Commercial layers and SPF WL hens were orally challenged with 108 CFU/ml Salmonella Enteritidis PT13a and SE nalR PT13, respectively. Crop lavage samples were collected at weekly intervals from day 0 (pre-challenge) to day 25-27 post-infection (pi) and bacteriological examination was performed to monitor progression of SE infection. Crop lavage samples were analyzed for SE-lipopolysaccharide (LPS)-specific IgA by enzyme-linked immunosorbent assay (ELISA). H&E stained slides of crop sections from day 34 pi and uninfected controls were assessed for lymphoid tissue via light microscopy. Lymphoid areas were graded based on morphology, size and cellularity using a score 0 to 5 scale. The score 0 to 5 (low to high) numerical values represented progressive increases in size and cellular density of lymphoid tissue. Bacterial culture results showed the highest percentage of SE positive crop lavage samples from all hen groups at day 5-6 pi and day 11-12 pi. A progressive decline in percentage of SE positive crop lavage samples did occur as time post-infection lengthened, however at day 25-27 pi SE persisted in crop lavage samples from SPF WL hens and three commercial white-egg layer strains. A marked increase in SE-LPS-specific IgA was measured in crop lavage samples between day 0 and day 11-12 pi for all hen groups. Crop SE-LPS-specific IgA response remained elevated above day 0 baseline for the duration of the experiment. Well-defined score 3 to 5 lymphoid tissue aggregates were observed in crop tissue sections harvested at day 34 pi. Comparison of crop sections determined a 1.2-4.0 times increase in ratio of lymphoid tissue in day 34 pi SE-challenged hens versus uninfected control hens.