Baicalin attenuated Mycoplasma gallisepticum-induced immune impairment in the chicken Bursa of fabricius through modulation of autophagy and inhibited inflammation and apoptosis

Background: Mycoplasma gallisepticum (MG) is the primary etiologic agent of chronic respiratory disease (CRD) in poultry. However, the mechanism underlying MG-induced immune dysregulation in chicken is still elusive. Baicalin showed excellent anti-bacterial, anti-inflammatory, anti-carcinogenic and anti-viral properties. In the present study, the preventive effects of baicalin against immune impairment in the chicken Bursa of fabricius (BF) were studied in an MG-infection model.

Results: Histopathological examination showed increased inflammatory cells infiltrations and fragmented nuclei in the model group. Ultrastructural analysis revealed the phenomenon of apoptosis in the bursal cells, along with the deformation of mitochondrial membrane and swollen mitochondria in the model group. However, these abnormal morphological changes were partially alleviated by baicalin. Meanwhile, baicalin-treatment attenuated the level of pro-inflammatory cytokines, and suppressed nuclear factor-kappa B (NF-κB) expression both at protein and mRNA level. Terminal deoxynucleotidyl transferase-mediated dUTP nick endlabeling (TUNEL) assay showed extensive apoptosis in BF in the model group. The mRNA and protein expression level of apoptosis-related genes were upregulated in BF. While, baicalin treatment significantly alleviated apoptosis in the BF. In addition, alteration in mRNA and protein expression level of autophagy-related genes and mitochondrial dynamics proteins were significantly alleviated by baicalin. Moreover, baicalin-treatment significantly attenuated MG-induced decrease in CD8⁺ cells and reduced bacterial load in chicken BF compared to model group.

Conclusion: These results suggested that baicalin could effectively inhibit MG-induced immune impairment and alleviated inflammatory responses and apoptosis in the chicken BF. This article is protected by copyright. All rights reserved.

Keywords: Apoptosis; Baicalin; Bursa of fabricius; Immune impairment; Mycoplasma gallisepticum.