Circulating miR-155, a potential regulator of immune responses to different vaccines in chicken

Vaccination is one of effective means to prevent viral infectious diseases in poultry. However, the functions of circulating miRNAs in immune response remain unknown. In this study, miR-155, a key factor in the regulation of immune function, was selected to study its expression, potential function and mechanism in the 12-day-old chicken immune responses to three vaccines (avian influenza virus inactivated vaccine, Newcastle disease virus attenuated vaccine and infectious bursal disease virus attenuated vaccine), respectively. The experiment aimed to explore the relationships between the expression levels of serum circulating miR-155 and immune responses. The results showed that the expression levels of serum circulating miR-155 were significantly different during the three immune responses, but had similarities at several time points post inoculation. 2 day post inoculation (dpi), 5dpi, and 21dpi were the possible common key time points of the three immune responses. Moreover, spleen (2dpi), bursa of Fabricius and cecal tonsil (5dpi), and liver (21dpi) were the possible key tissues associated with the differential expression levels of serum circulating miR-155. Bioinformatics analysis showed that several key target genes (such as KRAS, RAP1B, and RPS6KA3) of miR-155 possibly played a key role in immune function regulation through MAPK and mTOR signaling pathways. The study can lay the foundation for further studying the function and application of circulating miR-155 in chicken immune responses.