Mycoplasma gallisepticum Infection Impaired the Structural Integrity and Immune Function of Bursa of Fabricius in Chicken: Implication of Oxidative Stress and Apoptosis.

Wei Zhang,Syed Waqas Ali Shah,Muhammad Ishfaq,Jian Wang,Qiaomei Zhang,Jichang Li,Zhiyong Wu,Yuhao Liu

doi:10.3389/fvets.2020.00225

Abstract

Mycoplasma gallisepticum (MG) induces a dysregulated immune response in the lungs and air ways of poultry. However, the mechanism of MG-induced immune dysregulation is still not completely understood. In the present study, the effect of MG-infection on chicken bursa of fabricius (BOF) is investigated. Histopathology, electron microscopy, TUNEL assay, qRT-PCR and western blot were employed to examine the hallmarks of oxidative stress and apoptosis. The data revealed that MG-infection induced oxidative stress and decreased antioxidant responses in BOF tissues compared to control group. Histopathological study showed pathological changes including reduction in lymphocytes and increased inflammatory cell infiltration in MG-infection group. Ultrastructural assessment represents obvious signs of apoptosis such as mitochondrial swelling, shrinkage of nuclear membrane and fragmentation of nucleus. Increased cytokine activities were observed in MG-infection group compared to control group. Meanwhile, the mRNA and protein expression level of apoptosis-related genes were significantly (p < 0.05) upregulated in MG-infection group. Terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) assay further confirmed that MG induced apoptosis in BOF tissues as TUNEL-stained positive nuclei were remarkably increased in MG-infection group. In addition, MG-infection significantly reduced the number of CD8+ lymphocytes in chicken BOF at day 7. Moreover, bacterial load significantly increased at day 3 and day 7 in MG-infection group compared to control group. These results suggested that MG-infection impaired the structural integrity, induced oxidative stress and apoptosis in chicken BOF tissues, which could be the possible causes of damage to immune function in chicken BOF.

Highlights

Mycoplasma gallisepticum (MG) belongs to the class Mollicutes and the family Mycoplasmataceae [1]
The property of cytoadherence of MG produced additional virulence factors including superoxide radicals leading to immune dysregulation [4, 7]
Compared to control group, increased number of positive stained nuclei were observed in chicken bursa of fabricius (BOF) tissues in MG-infection group. These results suggested that MG-infection remarkably increased the number of apoptotic cells in chicken BOF and could impair its immune function

Summary

Introduction

Mycoplasma gallisepticum (MG) belongs to the class Mollicutes and the family Mycoplasmataceae [1]. MG is an important avian pathogen that mainly infect chickens’ respiratory tract and causes chronic inflammation in airway passages and lungs. Previous studies demonstrated that MG is the primary cause of chronic respiratory disease in chickens and infectious sinusitis in turkeys, characterized by nasal discharge, sneezing, and coughing [2, 3]. Researchers reported that MG-infection causes significant economic losses to the poultry industry including the reduction in egg production, hatchability, and low meat quality [4,5,6]. MGinfection induces respiratory distress, profound inflammatory response in mucosal tissues and immune dysregulation in chickens [4]. The property of cytoadherence of MG produced additional virulence factors including superoxide radicals leading to immune dysregulation [4, 7]. The mechanism underlying immune dysregulation induced by MGinfection is still unclear

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Conclusion