MHC class II antigen expression by ocular cells in proliferative diabetic retinopathy

An immunohistological study was performed on ciliary biopsies of the pars plana obtained surgically in 10 patients suffering from diabetic retinopathy and on 15 surgical specimens of pre-retinal neovascularized membranes. Using immunofluorescence and immunoperoxidase procedures, linear deposits of IgG, IgA and complement components were found in the 8 pars plana from patients with proliferative diabetic retinopathy, at the basal pole of the pigment epithelial cells and within the stroma. In contrast, these deposits were absent from normal pars plana and from the cases of background retinopathy. Moreover, pigment and non-pigment epithelial cells were found to express HLA DR and DQ determinants, in six of the eight patients with proliferative retinopathy. Immunohistological examination of pre-retinal membranes showed deposition of immunoglobulins and complement components within the connective stroma and along the new blood vessels. Endothelial cells of the newly formed vascular walls strongly expressed class II antigens on their membrane, as well as scattered stromal cells. As neither pigment epithelial cells nor retinal vascular endothelial cells normally express class II determinants, our results suggest the involvement of immunological phenomena in intraocular proliferative diseases and eventual interactions between the immune system and peptide growth factors. However, whether or not this immune reaction plays a role in the initiation or extension of intra-ocular proliferation remains to be determined.