Abstract: Objective　To investigate the effect of Mycobacterium tuberculosis (Mtb)-infected type Ⅱ alveolar epithelial cells (AECⅡ)-derived exosomes (Exos) on the polarization of macrophages. Methods　Experiment 1: AECⅡ and Mtb strain H37Rv were cultured in vitro. AECⅡ was infected with Mtb and Exos, and was isolated. Exos were divided into the AECⅡ group and the Mtb-AECⅡ group. Transmission electron microscopy (TEM) and nanoparticle tracking analysis (NTA) were used to observe the morphology of Exos and to measure the number and size of Exos. Flow cytometry was used to identify the expressions of Exos surface characteristic markers CD63, CD81 and HSP70. BCA method was used to measure the protein content of Exos. miRNA microarray was used to detect and verify the differential miRNA expression profile between the two groups. Enzyme-linked immunosorbent assay (ELISA) was used to detect the levels of tumor necrosis factor-α (TNF-α), interleukin 6 (IL-6) and IL-10 in the cell culture supernatant. Experiment 2: AECⅡ was separated into the control group, the mimic-NC group, the miR-145 mimic group, the inhibitor-NC group and the miR-145 inhibitor group. After AECⅡ was transfected with lentivirus that overexpressed or silenced miR-145, AECⅡ was infected by Mtb, and then Exos were isolated. Real-time fluorescence quantitative PCR (qPCR) was used to measure the level of miR-145 in Mtb-AECⅡ Exos after transfection. Flow cytometry was used to detect the expression levels of M1 type marker (CD86) and M2 type marker (CD163) of macrophages, and qPCR was used to detect the levels of miR-145, TNF-α, inducible nitric oxide synthase (iNOS), arginase 1 (Arg-1) and IL-10 mRNAs in macrophages. Results　Experiment 1: Mtb-infected AEC Ⅱ secreted Exos as spherical vesicles with a diameter of about 100 nm. CD63, CD81 and HSP70 were all positive in Exos. Compared with the AECⅡ group, the quantity and protein content of Exos, levels of miR-145 and IL-10 were increased in the Mtb-AECⅡ group (P＜0.05), and levels of TNF-α and IL-6 were decreased (P＜0.05). Experiment 2: compared with the control group, the level of miR-145 in Mtb-AECⅡ Exos, the percentage of CD163-positive macrophages, the levels of miR-145, Arg-1 mRNA and IL-10 mRNA in macrophages were increased in the miR-145 mimic group (P＜0.05), and the percentage of CD86-positive macrophages, the levels of TNF-α mRNA and iNOS mRNA in macrophages were reduced (P＜0.05). Changes of the above indicators in the miR-145 inhibitor group were opposite to those in the miR-145 mimic group. Conclusion Mtb infection with AECⅡ-derived Exos may stimulate M2 type polarization of macrophages and inhibit M1 polarization through miR-145, thus resisting inflammation.

Key words: mycobacterium tuberculosis, macrophages, alveolar, alveolar epithelial cells, exosomes, gene expression regulation, type Ⅱ alveolar epithelial cells, microRNA-145