Dynamic immune response to Avian Pathogenic Escherichia coli infection in broiler chickens: Insights into pro-inflammatory and anti-inflammatory cytokine regulation: CYTOKINE REGULATION IN APEC INFECTED BROILERS.

Avian Pathogenic Escherichia coli (APEC) poses a significant threat to the U.S. poultry industry, causing respiratory infections and systemic colibacillosis. Understanding APEC's impact on the immune response is crucial for developing effective prevention and treatment strategies. This study investigates the dynamic immune responses to APEC infection in broiler chickens, with a focus on survival rates, airsac lesion scores, and cytokine gene expression patterns in lung tissue. Seven-day-old broiler chicks were divided into control and APEC-inoculated groups, with the control group receiving tryptic soy broth and the APEC group receiving 7 × 10 CFU of APEC via intratracheal inoculation. Survival data included both male and female birds, while airsac lesion score and lung tissue samples for gene expression analyses were collected only from male birds at nine time points post-infection (days 1, 3, 5, 7, 9, 11, 13, 15, and 21). High airsac lesion incidence and mortality were observed during early infection stages, decreasing in mid to later stages as anti-inflammatory cytokines were upregulated. The lung gene expression study analyzed the expression of pro-inflammatory cytokines (IFN-γ, IL-1β, IL-8, and IL-6), regulator (SOCS3), and anti-inflammatory cytokines (IL-10, TGFβ-2, TGFβ-3, and IL-1RN) via RT-qPCR assays, using 18S rRNA for normalization. A two-way ANOVA followed by Tukey's Kramer test evaluated the effects of APEC treatment and days post-infection on gene expression, with the Mann-Whitney U test comparing fold changes between groups. Results indicated an early upregulation of pro-inflammatory cytokines like IFN-γ and IL-1β, followed by the modulatory roles of SOCS3, TGF-β, and IL-1RN, balancing the immune response and possibly preventing excessive tissue damage. This study elucidates the dynamic regulation of key cytokines during APEC infection in chickens, providing insights into immune mechanisms. Understanding these mechanisms is crucial for developing targeted therapies and improving disease management in poultry, potentially reducing antibiotic dependence and enhancing overall poultry health and productivity.