Although immune responses are essential to protect the body from infection, they can also harm tissues. Certain tissues and organs, including the eye, constitute specialized microenvironments that locally inhibit immune reactivity. Dedicator of cytokinesis protein 2 (DOCK2) is a Rac-specific guanine nucleotide exchange factor (GEF) that is predominantly found in hematopoietic cells. DOCK2 plays a key role in immune surveillance because it is essential for the activation and migration of leukocytes. DOCK2 mutations cause severe immunodeficiency in humans. We found that DOCK2-mediated Rac activation and leukocyte migration were effectively inhibited by cholesterol sulfate (CS), but not by cholesterol or other sulfated steroids. CS bound to the catalytic domain of DOCK2 and suppressed its GEF activity. Mass spectrometric quantification revealed that CS was most abundantly produced in the Harderian gland, which provides the lipids that form the oily layer of the tear film. Sulfation of cholesterol is mediated by the sulfotransferases SULT2B1b and, to a lesser extent, SULT2B1a, which are produced from the same gene through alternative splicing. By genetically inactivating Sult2b1, we showed that the lack of CS in mice augmented ultraviolet- and antigen-induced ocular surface inflammation, which was suppressed by administration of eye drops containing CS. Thus, CS is a naturally occurring DOCK2 inhibitor and contributes to the generation of the immunosuppressive microenvironment in the eye.

尽管免疫反应对于保护人体免受感染至关重要，但它们也会伤害组织。某些组织和器官，包括眼睛在内，构成了局部抑制免疫反应性的特殊微环境。胞质分裂蛋白2（DOCK2）的指示剂是Rac特异性鸟嘌呤核苷酸交换因子（GEF），主要存在于造血细胞中。DOCK2在免疫监视中起关键作用，因为它对于白细胞的激活和迁移至关重要。码头2突变会导致人类严重的免疫缺陷。我们发现DOCK2介导的Rac激活和白细胞迁移被胆固醇硫酸盐（CS）有效抑制，但未被胆固醇或其他硫酸盐类固醇抑制。CS绑定到DOCK2的催化域，并抑制其GEF活性。质谱定量分析表明，CS是在Harderian腺中产生最多的，它提供形成泪膜油层的脂质。胆固醇的硫酸化是由磺基转移酶SULT2B1b和较小程度的SULT2B1a介导的，它们是通过替代剪接从同一基因中产生的。通过基因灭活Sult2b1，我们发现小鼠体内CS的缺乏加剧了紫外线和抗原诱导的眼表炎症，而服用含CS的眼药水可以抑制这种炎症。因此，CS是天然存在的DOCK2抑制剂，并且有助于在眼睛中产生免疫抑制性微环境。