PSVI-7 Evaluation of humoral immune response and serum biochemical changes in broiler chickens colonized with Campylobacter jejuni.

Abstract Campylobacter jejuni (Cj) is a leading cause of foodborne illness globally, often linked to consumption of poultry. Unfortunately, current strategies applied by industry to control Cj in poultry have had limited success. In this regard, understanding the humoral immune response and associated changes in serum biochemistry to C. jejuni colonization in broiler chickens is essential for developing effective vaccines, as biochemical markers provide insights into metabolic and inflammatory responses that may influence immunity and overall health. In this study, ten day-of-hatch chickens were used to assess maternal immunity (cecal mucus, blood, and yolk sac serum), and the cecal contents were analyzed for the presence of Cj. Additionally, 56 day-of-hatch chicks were randomly divided into eight treatment groups (n=7 birds/treatment), including a negative control (NC), and allocated to their respective pens. On days 3 and 4, birds were orally gavaged with 0.25 mL of vehicle (NC) or wild strains K1, K5, K6, S1, S3, S4, or 6-strain cocktail for respective groups (~1×107 CFU/mL). On day 14, samples were collected for microbiological (cecal contents), immunological (blood and cecal contents), and serum chemistry (blood) analyses. Cecal contents were diluted and plated on Campylobacter line agar plates to enumerate Cj. Blood, yolk sac, and cecal contents were processed to extract serum and mucus. Indirect ELISA was performed to determine anti-Cj IgM, IgY, and IgA levels. Blood serum samples were analyzed using Avian rotors on MicroChem II (MicroVet Diagnostics) equipment [total protein and fractions, liver enzymes (ALT, AST, TBA, TB, and GGT), creatinine kinase, uric acid, glucose, cholesterol, calcium, phosphorus, potassium, and sodium]. All the data were analyzed using one-way ANOVA followed by Dunnett’s post hoc comparison in GraphPad Prism 10 Software. P-value< 0.05 was considered significant. Microbiology analysis confirmed Cj colonization in all challenged groups except the negative control. Immunological analysis showed high titers of anti-Cj IgY in the yolk sac and blood serum, and anti-Cj IgA in the cecal mucus of day-of-hatch birds, strongly suggesting maternal immunity transference. Additionally, anti-Cj IgM levels were higher in all day 14 birds compared to day-of-hatch chickens, with a significant increase in all the K strains and the cocktail group, suggesting the development of an anti-Cj humoral immune response. Serum biochemistry results showed that wildtype strain S3 presented significantly higher Albumin:Globulin ratio, glucose, and cholesterol concentration than the negative control, suggesting a better nutritional status. All S strains presented an average lower globulin concentration than the negative control, suggesting a lower inflammatory response. The observed changes in serum biochemistry suggest potential markers for nutritional status and inflammatory response. In conclusion, our study found that C. jejuni induces a humoral immune response suitable for vertical transfer of immunity, providing a foundation for further C. jejuni vaccine studies.