Day-old vaccination with the Vaxsafe MG304 live-attenuated vaccine protects chickens from tracheal transcriptional changes induced by chronic infection with Mycoplasma gallisepticum

Administration of vaccines to one-day-old chicks has considerable advantages in the commercial poultry industry. We evaluated the efficacy of the live-attenuated Vaxsafe MG304 vaccine in day-old chicks using differential gene transcription analysis of the tracheal mucosa at 2 weeks after challenge. Infected unvaccinated chickens had two distinct transcriptional profiles, which corresponded to their tracheal mucosal thicknesses (TMTs). Infected unvaccinated chickens with a low TMT had a larger number of genes differentially transcribed (4920) than infected unvaccinated chickens with a high TMT (669), when compared to uninfected unvaccinated chickens. In the infected unvaccinated chickens with low TMTs, functions associated with mitochondrial dysfunction and DNA damage response were enriched with up-regulated genes, while functions associated with tissue repair and apoptosis were enriched with down-regulated genes. In the infected unvaccinated chickens with high TMTs, functions associated with the cytokine response, cell proliferation and the lymphocyte response were enriched with up-regulated genes, while functions associated with extracellular matrix organisation were enriched with down-regulated genes. The transcriptional profiles of the vaccinated infected chickens were similar to those of uninfected chickens, whether they had been vaccinated with a low or a high dose of Vaxsafe MG304. A greater number of genes were differentially transcribed in infected unvaccinated chickens with a low TMT than in infected unvaccinated chickens with a high TMT, when compared to vaccinated infected chickens. This study has demonstrated that Vaxsafe MG304 is efficacious when administered to day-old chicks, protecting against pathological transcriptional changes induced by infection with M. gallisepticum.