Authors: Fangliu Yu , Qingdeng Li , Wenqin Xu , Yunxing Gao , Yufeng Wen , Qiong Zhang , Jun Dou

Abstract

Background and Objective: Mycobacterium tuberculosis (Mtb) harbors immune evasion that impairs immune responses and prevents optimal immunity against Mtb. However, little is known about mechanisms of immune evasion in Mtb infected individual. In this study, the relationship among the IL-35 level, IL-35-producing regulatory T cells (iTr35) subset, the bacterial burden and lung lesions in mice infected with Mtb were investigated to assess the impact of immune evasion on the infected mice.
Methods: A total of twenty C57BL/6 male 6-7 weeks old mice, were injected with 1 × 105 colony-forming units (CFU) of attenuated H37Ra strain of Mtb in a volume of 200 μL, to prepare mouse tuberculosis infection models. Colony forming units in left lung and spleen coefficient were determined followed by histopathology, quantitative RT-PCR for mRNA, Western blot analysis, cytokine IL-35 detection and flow cytometry of fork head box protein P3-expressing T cells.
Results: Compared with the control mice, the mRNA expressions of the p35 and EBI3 of IL-35 were significantly increased in the spleen of 8-week infected mice, and their protein expressions were not only increased in 8-week but in lungs of 4-week infected mice, accompanied with an elevated level of serum IL-35. In addition, iTr35 subset was increased in the spleen of 8-week infected mice compared with the control mice. Importantly, the high bacterial burden, lung lesions, and low mouse weight were found in the 8-week infected mice.
Conclusion: The mice infected with Mtb H37Ra strain resulted in elevated IL-35 levels and iTr35 subset. There were increased bacterial burden and lung lesions, suggesting that IL-35 and iTr35 cells play an immune evasion role in chronic Mtb infected mice.

Keywords: Mycobacterium tuberculosis, H37Ra,IL-35,iTr3, Immune evasion.