LAUSR

A modified form of cholesterol protects the eye from immune cell invasion by inhibiting the Rac-specific GEF DOCK2. Evading the immune system with a lipid Some tissues, such as the eye, locally suppress immune cells or limit their ability to infiltrate the tissue. Sakurai et al. found that cholesterol sulfate (CS) inhibited the guanine nucleotide exchange factor DOCK2 and thus suppressed the migration of neutrophils and T cells in vitro. In mice, CS was produced by the gland that secretes the lipids that form the outer layer of the tear film covering the eye. Mice lacking the major sulfotransferase that produces CS from cholesterol exhibited increased infiltration of immune cells into the conjunctiva and the cornea in different in vivo models of ocular surface inflammation, which was reversed by topical application of CS. Identifying a role for CS in endogenous immunosuppression suggests that it or other bioactive lipids may play a role in other tissues that evade immune surveillance, such as tumors. 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.