Role of thrombospondin-1 in T cell response to ocular pigment epithelial cells.

Ocular pigment epithelium (PE) cells promote the generation of T regulators (PE-induced Treg cells). Moreover, T cells exposed to PE acquire the capacity to suppress the activation of bystander T cells via TGFbeta. Membrane-bound TGFbeta on iris PE cells interacts with TGFbeta receptors on T cells, leading to the conversion of T cells to CD8(+) Treg cells via a cell contact-dependent mechanism. Conversely, soluble forms of TGFbeta produced by retinal PE cells can convert CD4(+) T cells into Treg cells in a manner that is independent of cell contact. In this study, we looked at the expression of immunoregulatory factors (TGFbeta, thrombospondins, CD59, IL-1 receptor antagonist, etc.) in PE cells as identified via an oligonucleotide microarray. Several thrombospondin-binding molecules were detected, and thus we focused subsequent analyses on thrombospondins. Via the conversion of latent TGFbeta to an active form that appears to be mediated by thrombospondin 1 (TSP-1), cultured iris PE and retinal PE cells induce a PE-induced Treg cell fate. After conversion, both ocular PE and PE-induced Treg cells express TSP-1. Regulatory T cell generation was amplified when the T cells also expressed TSP-1. In addition, PE-induced Treg cells significantly suppressed activation of bystander T cells via TSP-1. These results strongly suggest that the ability of ocular PE and PE-induced Treg cells to suppress bystander T cells depends on their capacity to produce TSP-1. Thus, intraocular TSP-1 produced by both ocular parenchymal cells and regulatory T cells is essential for immune regulation in the eye. Keywords: Comparison Comparison of gene expression pattern in Mouse Primary Cultured Cell Lines (RPE, IPE, CBPE). Adult (6- to 8-week-old) C57BL/6 purchased from CLEA Japan Inc. (Tokyo, Japan) were used as donors ocular pigment epithelium (PE). To cultivate iris PE (IPE) and ciliary body PE (CBPE), iris and ciliary body tissues in the eyes were dissected out, and then incubated in 1 mg/ml Dispase and 0.05 mg/ml DNase I (both from Boehringer-Mannheim, Mannheim, Germany) for 1 hr. To cultivate retinal PE (RPE) Eyes were cut into two parts along a circumferential line posterior to the ciliary process, creating a ciliary body-deficient posterior eyecup. The eyecup was then incubated in 0.2% trypsin (Biowhitaker) for 1 hr. These tissues were triturated to make a single cell suspension, and then re-suspended in the medium.