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S. Masli, B. Turpie; Thrombospondin-1 Expressed by Tgfbeta-Treated Antigen Presenting Cells Promotes Treg Induction by Inhibiting Th17 Development. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4833.
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Expression of thrombospondin-1 (TSP-1) is critical to the ocular immune privilege as it contributes significantly to the regulatory immune response induced by TGF-β-exposed ocular antigen presenting cells (APCs). Such TGFβ-exposed APCs produce increased amounts of active TGFβ in a TSP-1-dependent manner and induce TGFβ-secreting regulatory T cells (Treg). In the context of a key role ascribed to TGFβ in the development of functionally disparate subsets, Treg and Th17, we now examine relevance of APC-derived TSP-1 in development of the former subset over the latter.
Thioglycollate-elicited peritoneal exudates cells from C57BL/6 (WT) or TSP1null mice were used as APCs. These cells, pulsed with ovalbumin, were cultured overnight in the presence or absence of TGFβ (5 ng/ml) before co-culturing with CD4+CD25- T cells from OT-II mice. Expression of FoxP3 was evaluated in CD4+CD25+ T cells by flow cytometry. Activated cells were restimulated in a fresh culture with plate bound anti-CD3 and IL-17, IL-6 and TGFβ in culture supernatants were measured by ELISA. Expression of IL-23 by LPS-stimulated WT APCs in the presence of TSP1 or peptide derived from the C-terminal domain of TSP-1 or control peptide was assessed by real-time PCR and ELISA.
The number of CD4+CD25+FoxP3+ T cells increased among T cells co-cultured with TGFβ-treated WT APCs as compared to untreated APCs, which corresponded with their significantly decreased ability to secrete IL-6 and IL-17 as compared to the controls. Exposure of TSP1null APCs to TGFβ failed to do so. Untreated TSP1null APCs induced significantly increased level of IL-17 secretion by activated T cells as compared to the WT control APCs. Exposure of WT APCs to both TGFβ and TSP1 derived peptide led to inhibition of Th17-promoting cytokine IL-23, while CD4+CD25- T cells treated with TSP1 derived peptide increased expression of TGFβ and Foxp3 as compared to those exposed to control peptide.
Regulatory response induced by TGFβ-exposed APCs includes immunosuppressive CD4+CD25+FoxP3+ Tregs, development of which is facilitated by APC-derived TSP1 over that of inflammatory Th17 effectors in a TGFβ-independent manner.
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