Abstract
Purpose: :
To investigate whether T cells exposed to ocular pigment epithelial cells (PE) express CD25 and Foxp3, and the CD25+ PE–T cells display regulatory functions in vitro.
Methods: :
Primary cultured PE cells (iris PE or retinal PE) were established from normal C57BL/6 mice. T cells were co–cultured with PE, x–irradiated, and used as regulators (PE Tregs). Target bystander T cells were established from normal splenic T cells with anti–CD3 antibodies. T–cell activation was assessed for proliferation by [3H]–thymidine incorporation. The expression of CD25, GITR (glucocorticoid–induced TNF receptor family related gene), and CD103 on PE Tregs was evaluated by flow cytometry. T cells from CD25 deficient donors or CD25 depleted population were used to abolish regulatory function. The expression of Foxp3 transcripts on CD25+ PE Tregs was evaluated by semi–quantitative RT–PCR.
Results: :
Cultured iris PE and retinal PE converted naïve T cells to CD25+ Tregs that suppressed the activation of bystander T cells. These CD25+ PE Tregs expressed GITR and CD103 constitutively. Similar to CD25+ PE Tregs, CD25 negative PE Tregs suppressed the activation of bystander T cells. T cells depleted of CD25+ cells or T cells disrupted for CD25 molecules prior to in vitro stimulation by PE cells still differentiated into Tregs. The ocular PE cells converted in CD25+ Tregs that expressed Foxp3 transcripts through TGF–b TGF–b receptor interactions. In addition, membrane–bound TGF–b+ CD25+ PE T cells, that acquired regulatory functions, expressed transcripts for many immunomodulatory molecules and Foxp3 transcripts.
Conclusions: :
One subset of Tregs of ocular pigment epithelial cells arises from CD25 negative precursors, and the induction of T cell–suppression does not require the presence of natural (conventional) CD25 Tregs.
Keywords: immune tolerance/privilege • immunomodulation/immunoregulation • cytokines/chemokines