The observation that type II, or immune, interferon could be produced by peripheral-blood leukocytes in vitro on an immune-specific basis suggested that it also might be produced in vivo in various autoimmune disorders. We found immune interferon in the serums of patients with systemic lupus erythematosus, rheumatoid arthritis, scleroderma and Sjögren's syndrome. Among 28 patients with systemic lupus erythematosus, 71 per cent of those with active and 21 per cent of those with inactive disease showed interferon in their serums. Serial serum samples showed a good correlation between interferon titers and disease activity. Moreover, interferon titers correlated positively with antibodies to DNA and negatively with serum levels of the third component of complement. It is possible that the production of interferon may contribute to immunologic aberrations in auto-immune diseases and also protect the already compromised host from viral infections.

Toll-like receptors (TLRs) are crucial components of innate immunity that participate in host defense against microbial pathogens. We evaluated the expression and function of TLRs in human retinal pigment epithelial (RPE) cells. Real time PCR analysis revealed gene expression for TLRs 1-7, 9, and 10 in RPE cells. TLRs 1 and 3 were the most highly expressed TLRs. Protein expression for TLRs 2, 3, and 4 was observed on RPE cells and this expression was augmented by treatment with poly I:C or interferon-gamma (IFN-gamma). TLR 3 is the receptor for dsRNA, an intermediate of virus replication. Because RPE cells express TLR 3 and are frequently the site of virus replication within the retina, we evaluated TLR 3 signaling. RPE cells treated with poly I:C produced IFN-beta but not IFN-alpha, and this was inhibited by the treatment of RPE cells with anti-TLR 3 antibody. Human recombinant IFN-beta was shown to be biologically active on RPE cells by inhibiting viral replication. Poly I:C treatment of RPE resulted in an increase in the production of IL-6, IL-8, MCP-1, and sICAM-1. The presence of TLRs on RPE cells and the resultant TLR signaling in RPE cells suggest that these molecules may play an important role in innate and adaptive immune responses within the retina.

Vascular endothelial growth factor (VEGF) is a major agent in choroidal and retinal neovascularization, events associated with age-related macular degeneration (AMD) and diabetic retinopathy. Retinal pigment epithelium (RPE), strategically located between retina and choroid, plays a critical role in retinal disorders. We have examined the effects of various growth factors on the expression and secretion of VEGF by human retinal pigment epithelial cell cultures (HRPE). RT-PCR analyses revealed the presence of three isoforms of mRNA corresponding to VEGF 121, 165, and 189 that were up regulated by TGF-beta1. TGF-beta1, beta2, and beta3 were the potent inducers of VEGF secretion by HRPE cells whereas bFGF, PDGF, TGF-alpha, and GM-CSF had no effects. TGF-beta receptor type II antibody significantly reversed induction of VEGF secretion by TGF-beta. In contrast activin, inhibin and BMP, members of TGF-beta super family, had no effects on VEGF expression in HRPE. VEGF mRNA levels and protein secretion induced by TGF-beta were significantly inhibited by SB203580 and U0126, inhibitors of MAP kinases, but not by staurosporine and PDTC, protein kinase C and NF-kappaB pathway inhibitors, respectively. TGF-beta also induced VEGF expression by fibroblasts derived from human choroid of eye. TGF-beta induction of VEGF secretion by RPE and choroid cells may play a significant role in choroidal neovascularization (CNV) in AMD. Since the secretion of VEGF by HRPE is regulated by MAP kinase pathways, MAP kinase inhibitors may have potential use as therapeutic agents for CNV in AMD.