The changing face of corneal graft rejection

The cornea is the most commonly transplanted human tissue. It is estimated that globally over 65 000 corneal transplants are being performed each year.1 Over 16 000 corneal transplants were performed in the UK alone since 2005.2 The cornea is largely considered to be an immune privileged site. There are several attributes that contribute to this notion such as the compact architecture of the corneal stroma, which is believed to retard migration of immune cells; the physiological blood–aqueous barrier that prevents any immunogenic mediators and cells entering the ocular tissue3; the relative lack of lymphatics and blood vessels; the presence of unique factors within the ocular fluids like transforming growth factor-β, calcitonin gene-related peptide, melanocyte stimulating hormone and vasoactive intestinal peptide and cortisol binding globulin,4–6 which contribute to immune modulation/anterior chamber associate immune deviation wherein antigen introduced in to the anterior chamber results in antigen specific suppression of delayed hypersensitivity7; mucosal tolerance induced by conjunctiva associated lymphoid tissue,8 and constitutive expression of Fas ligand which promotes apoptosis in cells bearing Fas such as lymphocytes.9 Notwithstanding the above, immune mediated graft rejection is the single most important cause of graft failure. Although the 1-year survival rate is around 87%, it steadily falls thereafter.10 The reported rate …