T lymphocytes represent an important part of adaptive immune system undertaking different functions to regulate immune responses. CD4+ T cells are the most important activator cells in inflammatory conditions. Depending on the type of induced cells and inflamed sites, expression and activity of different subtypes of helper T cells are changed. Recent studies have confirmed the existence of a new subset of helper T lymphocytes called Th9. Naive T cells can differentiate into Th9 subtypes if they are exposed simultaneously by interleukin (IL) 4 and transforming growth factor β and also secondary activation of a complicated network of transcription factors such as interferon regulatory factor 4 (IRF4) and Smads which are essential for adequate induction of this phenotype. Th9 cells specifically produce interleukin 9 and their probable roles in promoting intestinal inflammation are being investigated in human subjects and experimental models of ulcerative colitis (UC). Recently, infiltration of Th9 cells, overexpression of IL-9, and certain genes associated with Th9 differentiation have been demonstrated in inflammatory microenvironment of UC. Intestinal oversecretion of IL-9 protein is likely to break down epithelial barriers and compromise tolerance to certain commensal microorganisms which leads to inflammation. Th9 pathogenicity has not yet been adequately explored in UC and they are far from being considered as inflammatory cells in this milieu, therefore precise understanding the role of these newly identified cells in particular their potential role in gut pathogenesis may enable us to develop novel therapeutic approaches for inflammatory bowel disease. So, this article tries to discuss the latest knowledge on the above-mentioned field.

T淋巴细胞代表适应性免疫系统的重要部分，承担着调节免疫反应的不同功能。CD4 + T细胞是炎症条件下最重要的激活细胞。根据诱导细胞和发炎部位的类型，辅助T细胞的不同亚型的表达和活性会改变。最近的研究已证实存在称为Th9的辅助T淋巴细胞的新子集。如果原始T细胞同时被白介素（IL）4和转化生长因子β以及复杂的转录因子网络（如干扰素调节因子4（IRF4）和Smads）所必需的二次激活，则它们可以分化为Th9亚型。该表型的充分诱导。Th9细胞特异性产生白介素9，并且在人类受试者和溃疡性结肠炎（UC）实验模型中研究了它们在促进肠道炎症中的可能作用。最近，在UC的炎性微环境中已经证明了Th9细胞的浸润，IL-9的过表达以及与Th9分化相关的某些基因。肠道中IL-9蛋白的过度分泌可能会破坏上皮屏障并损害对某些共生微生物的耐受性，从而导致炎症。在UC中尚未充分研究Th9的致病性，因此远没有将Th9的致病性视为炎症细胞，因此，准确了解这些新发现的细胞的作用，尤其是它们在肠道发病机理中的潜在作用，可能使我们能够开发出治疗炎症性肠病的新方法。因此，本文试图讨论上述领域的最新知识。