Transcriptional profiling analysis of host response to Clostridium perfringens infection in broilers

Necrotic enteritis is a disease caused by Clostridium perfringens, which threatens poultry production in the absence of dietary antibiotics. A total number of 600 Ross broilers were reared in 12 pens with each hosting 50 birds. Each 6 pens of birds were fed medicated (bacitracin at 55 mg/kg) or nonmedicated starter diets immediately after the chicks were placed. At d 18, birds were challenged with C. perfringens (10(7) cfu/mL mixed with feed). Spleens were collected from 12 birds of each group (2 birds per pen randomly) at d 18 (before infection), 19, 20, and 22. A low-density chicken immune microarray was used to study gene expression profiling of host response to C. perfringens infection. Six biological replicates (2 birds per biological replicate) for each treatment group were labeled with either Cy5 or Cy3 with dye swap. A total of 24 arrays were used for this study. Gene signal intensity was globally normalized by locally weighted regression and smoothing scatter plots and expressed on a natural log scale. A mixed model including treatment, time, array, subgrid (random effect), dye, and all interactions among treatment and time was used to identify differentially expressed genes between postinfection vs. preinfection, among postinfections, and between medication treatments, at the 5% significance level. The results indicated subtle medication effects on gene expression of these immune-related genes compared with bacterial infection effect. Our findings strongly suggest that both cell-mediated and antibody-mediated immune responses via MHC class I and II systems were actively involved in the host defense against C. perfringens infection in broilers. The unique cytokine signaling pathway and apoptosis cascade found in the study provide a new insight of molecular regulation of host immune response. Collectively, the findings of the present study will shed light on the molecular mechanisms underlying C. perfringens infection in broilers.