Abstract
The thymus is a primary lymphoid organ and plays a critical role in the immune response against infectious agents. Baicalin is a naturally derived flavonoid famous for its pharmacological properties, but the preventive effects of baicalin against immune impairment remain unclear. We examined this effect in the context of Mycoplasma gallisepticum (MG) infection-induced structural damage in the chicken thymus. Histopathological examination showed that the compact arrangement of cells in the thymus was lost in the MG-infected group. Inflammatory cell infiltration and nuclear debris accumulated, and the boundary between the cortex and medulla was not clearly visible. The mRNA and protein expression of apoptosis-related genes were significantly increased in the MG-infected group compared to the control group and the baicalin group. The number of positively stained nuclei in the terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling (TUNEL) assay were increased in the MG-infected group. In addition, electron microscopic examination showed chromatin condensation, mitochondrial swelling and apoptotic vesicles in the MG-infected group. However, baicalin treatment significantly alleviated the oxidative stress and apoptosis induced by MG infection. Importantly, the abnormal morphology was partially ameliorated by baicalin treatment. Compared to the MG-infected group, the baicalin-treated group showed significantly reduced expression of apoptosis-related genes at both the mRNA and protein levels. Meanwhile, the nuclear factor erythroid 2-related factor 2 (Nrf2) signalling pathway and downstream genes were significantly upregulated by baicalin to counteract MG-induced oxidative stress and apoptosis in the thymocytes of chickens. In summary, these findings suggest that baicalin treatment efficiently attenuated oxidative stress and apoptosis by activating the Nrf2 signalling pathway and could protect the thymus from MG infection-mediated structural and functional damage.
Highlights
Mycoplasma gallisepticum (MG) are wall-less prokaryotic microorganisms that belong to the family Mycoplasmataceae and class Mollicutes [1]
Our data revealed that MG infection induced oxidative stress in the thymus of white leghorn chickens
These findings are in agreement with previous studies [4] that microscopic lesions, including mild to moderate congestion and lymphocyte depletion, were prominent in the thymus of chickens infected with MG
Summary
Mycoplasma gallisepticum (MG) are wall-less prokaryotic microorganisms that belong to the family Mycoplasmataceae and class Mollicutes [1]. MG is the primary aetiologic agent of infectious sinusitis in game birds, turkeys, passerine birds and pigeons of all ages and chronic respiratory disease in chickens [2]. This pathogen is highly virulent and causes major economic losses in the poultry industry worldwide. Birds lacking a thymus are unable to clear MG infection, and increased lesions were observed in these birds compared to normal birds [7] These findings showed that a fully functional humoural and cellular immune system is essential to eliminate MG infections. The effect of MG infection on thymus function is still elusive and needs to be studied
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