RESUMO
Avibacterium paragallinarum is the causative agent of Infectious Coryza (IC), which is an upper respiratory tract disease in chickens. The occurrence of outbreaks has emphasized the significance of the disease globally in the chicken industry. Studies have demonstrated that early immune responses are critical in defining the severity and physiological outcome of an infection. This prompted the need to investigate the regulation of immune functions by the number of genes that are expressed during the chickens' response to A. paragallinarum serovar C3 insult. This study consisted of 15 male leghorn birds that were scored into groups (score 1, 2, 3) according to severity of symptoms after they were challenged. Expression patterns of immunity-related genes were followed as symptoms progressed from a disease score of 1 to 3. The data proposed that initial pathogen recognition was either through Toll-like receptors 2 or 4. Unique expression patterns were observed such as the up-regulation of TLR7 which recognizes viral-like particles. This substantiated the presence of prophages reported in the genome of A. paragallinarum. Significant down-regulation of metabolic pathways was observed, which led us to hypothesize that the host may rely on an oxidative stress response as initial immune response. The data sheds light onto the mechanisms that govern the immune system towards infection and/or towards the initial response to infections with highly virulent A. paragallinarum.