Th9 is a subset of CD4⁺ T cells that mainly secrete IL-9. Th9/IL-9 participates in immune response during Staphylococcus aureus and methicillin-resistant Staphylococcus aureus pneumonia (MRSA) infection. Here, we collected bronchoalveolar lavage fluid (BALF) from 30 children with MRSA pneumonia (MRSA group) and 10 children with bronchial foreign bodies (Control group). RT-PCR, ELISA and flow cytometry were used to detect the expression of miR-155 and IL-9 in BALF and the number of Th9 cells. CD4⁺ T cells isolated from BALF of MRSA and Control group were transfected with miR-155 mimic or inhibitor, and then induced Th9 cell differentiation. The results showed that the expression of miR-155 and IL-9 were significantly increased in BALF and Th9 cell of MRSA group, as well as the number of Th9 cells. miR-155 mimic upregulated IL-9 mRNA expression, IL-9 secretion and increased number of Th9 cells. On the contrary, miR-155 inhibitor inhibited IL-9 mRNA expression, IL-9 secretion and decreased number of Th9 cells. The dual luciferase assays demonstrated miR-155 can target binding to SIRT1 3′UTR. Moreover, overexpression of SIRT1 could reverse the effect of miR-155 mimic on IL-9 expression level, Th9 cell number and transcription factors PU.1 and IRF4 expression. In conclusion, miR-155 regulates Th9 differentiation in children with MRSA by targeting SIRT1.

Th9 是主要分泌 IL-9 的 CD4 ⁺ T 细胞的一个子集。Th9/IL-9 在金黄色葡萄球菌和耐甲氧西林金黄色葡萄球菌肺炎 (MRSA) 感染期间参与免疫反应。在这里，我们收集了 30 名 MRSA 肺炎患儿（MRSA 组）和 10 名支气管异物患儿（对照组）的支气管肺泡灌洗液（BALF）。采用RT-PCR、ELISA和流式细胞仪检测BALF中miR-155和IL-9的表达及Th9细胞数量。CD4 ⁺从MRSA和对照组的BALF中分离的T细胞转染miR-155模拟物或抑制剂，然后诱导Th9细胞分化。结果显示miR-155和IL-9在MRSA组BALF和Th9细胞中的表达明显增加，Th9细胞数量也明显增加。miR-155 模拟上调 IL-9 mRNA 表达、IL-9 分泌和增加的 Th9 细胞数量。相反，miR-155抑制剂抑制IL-9 mRNA表达、IL-9分泌和Th9细胞数量减少。双荧光素酶测定表明 miR-155 可以靶向结合 SIRT1 3'UTR。此外，SIRT1的过表达可以逆转miR-155模拟物对IL-9表达水平、Th9细胞数量和转录因子PU.1和IRF4表达的影响。综上所述，