Purpose The neonatal Fc receptor (FcRn) continues to be known to modulate IgG transport and protect against IgG catabolism, resulting in extension of the serum half-life of IgG. to the conjunctival lymphatic vessels but not in the conjunctival blood vessels. In the ciliary body, the FcRn receptor was found to be expressed in both the nonpigmented ciliary epithelium and the ciliary blood vessels. The expression AZD1152-HQPA of FcRn receptor was confirmed in the retinal blood vessels, iris blood vessels, optic nerve vascular structures, corneal epithelium and endothelium, and lens epithelium. Conclusions The FcRn receptor is usually expressed in multiple ocular tissues. The bloodCocular barrier showed FcRn receptor expression, indicating that IgG transport from ocular tissues to the blood system may use this receptor. The role of the FcRn receptor in the anterior segment and the conjunctiva remains unclear. The neonatal Fc receptor (FcRn, FcRp, or Fcgrt) is usually a heterodimer composed of major histocompatibility complex (MHC)-I, AZD1152-HQPA which binds to both albumin and the Fc portion of immunoglobulin G (IgG).1,2 Unlike other Fcreceptors that bind to the lower hinge region and top of the C2007;48:ARVO E-Abstract 22; Csaky KG, et al. 2007;48:ARVO E-Abstract 4936). Therefore, one might hypothesize that FcRn expressed at the bloodCretinal barrier functions in a way similar to that at the bloodC brain barrier, transporting IgG from the retina into the systemic circulation. Whether the FcRn receptor plays a role in transport of IgGs from the ocular tissue to the blood system remains to be determined. However, recent widespread use of intra-vitreous therapeutic IgGs, including rituximab for the treatment of intraocular lymphoma and bevacizumab for choroidal neovascularization, suggests that further investigation of the role of FcRn in IgG pharmacokinetics is critical. The FcRn receptor was detected in the lymphatic vessels but not in the blood vessels of the conjunctiva. The FcRn receptor modulates IgG transport and protects IgG in PRKAA2 the blood from catabolism.3,23 Therefore, it may be that this function of the FcRn receptor in the conjunctival lymphatic vessels is to act as an efflux receptor for the AZD1152-HQPA efficient elimination of antigenCantibody IgG complexes from the conjunctival space. Since the conjunctival blood vessels do not form a tight junction barrier, IgG from the blood system can enter into the conjunctival tissue interstitium by pinocytosis and/or convective transport through paracellular skin pores in the vascular endothelial level. Extravasated IgG is certainly then eliminated through the conjunctival tissue in to the lymphatic vessels via convective transportation with lymph liquid.24 The antigen-antibody complex could be more efficiently eliminated via lymphatic vessels if convective transport into the lymph fluid is supplemented by FcRn receptor-mediated transcytosis. In the cornea, the FcRn receptor was expressed in the corneal epithelium and the endothelium, the same locations in which Fcreceptors are expressed.25 In this case, the FcRn receptor may deliver antibodies to AZD1152-HQPA the cornea when corneal stromal antigen deposition occurs. FcRn receptor expression was also detected in the nonpigmented ciliary epithelium. The expression locations of FcRn receptor in the anterior segment are again consistent with that of Fcreceptors. Tripathi et al.25 suggested that this expression of Fcreceptors, as well as the recent demonstration of class II MHC molecules in the anterior segment of the eye, is involved in antigen presentation, in addition to regulation, maintenance, and defense of the aqueous outflow pathway. In the aqueous humor, low levels of immunoglobulins can be expected because of the integrity of the bloodCaqueous barrier and an active drainage mechanism that prevents accumulation of the immunoglobulins.26 How macromolecules enter the aqueous humor has not been clearly demonstrated. Raviola19 proposed that proteins enter the aqueous.