Haemopoietic Stem Cell Transplant (HSCT) is used as a treatment for a number of conditions particularly leukaemias. Following conditioning and HSCT, there is a ‘resetting’ of the immune system, which reconstitutes over a number of months. Graft-versus-Host Disease (GvHD) is a life-threatening complication of HSCT that includes severe, sight-threatening dry eye disease. In GvHD transplanted immune cells mount an immune response against the host. This thesis investigated how the immune cells of the conjunctiva are affected by HSCT and how the ocular surface leukocytes reconstitute. A non-invasive technique, ocular surface impression cytology (OSIC), was used to demonstrate that whilst there was no apparent depletion of innate immune cells in the conjunctiva, there was a marked reduction in the lymphocytes, which gradually reconstituted, returning to normal levels at the 6 months timepoint. Secondly OSIC was used to profile the leukocyte population in a cohort of patients post-HSCT with and without eye disease. In patients with dry eye disease following HSCT, the conjunctiva contained increased CD8+ lymphocytes, macrophages and neutrophils; a pattern that was distinct to that found in patients with dry eye disease following HSCT.

Age-related macular degeneration (AMD) is the leading cause of irreversible blindness in the developed world, but the mechanisms leading to AMD are poorly understood. Circulating retinal autoantibodies and antibody deposits in the retina are associated with AMD but despite this relationship, immune complex (IC)-mediated responses and underlying mechanisms of inflammation in the retina have not been characterised. IgG antibodies can activate immune effector function through formation of IC and their interaction with Fcγ receptors (FcγR) expressed by immune cells. This study aims to test the hypothesis that IC formed in the retina induce an inflammatory response following interaction with activating FcγRs expressed on microglia and/or macrophages, which may contribute to the pathogenesis of AMD. To study the biological effect of IC formation in the retina a model of IC injury was developed and fully characterised. The involvement of mouse FcγRs (mFcγRs) was first studied using Fc gamma chain deficient (γ-/-) mice, lacking cellular expression of activating mFcγRs, and further characterised using FcγRI-/-, FcγRIII-/- and FcγRIV-/- mice. The presence of IC and human FcγR (hFcγR) expression was investigated in human donor eyes from early and wet AMD patients and healthy controls. Finally the effect of inflammatory mediators on human retinal pigmented epithelium (RPE) function was investigated by direct stimulation with cytokines or indirect stimulation using conditioned medium of polarised human macrophages. IC deposition in the mouse retina led to an inflammatory response that depended on the presence of activating mFcγRs, particularly mFcγRI and mFcγRIII, but not on mFcγRIV. Immune complex deposition and increased numbers of immune cells expressing hFcγRIIa and hFcγRIIb were found in the choroid of early AMD donors and microglia in the retina of wet AMD donor eyes. Finally, macrophage activation differentially impacted on RPE cell function, with regards to barrier function and VEGF secretion. The results in this thesis support the hypothesis that immune complex-mediated inflammation could play a role in the pathogenesis of AMD.