Purpose: To determine whether murine corneal endothelial (CE) cells can promote the generation of T regulatory (Treg) cells in vitro.
Methods: To induce Treg cells in vitro by CE cell lines, T cells exposed to CE cells were used as Treg cells. T cells exposed to CE cells in the presence of anti-mouse CD3 antibody were harvested and added to target bystander T cells in vitro. T-cell activation was assessed for proliferation by [(3)H]-thymidine incorporation. Expression of CD25 or Foxp3 on Treg cells was evaluated by flow cytometry. Expression of cytotoxic T-lymphocyte antigen-2 alpha (CTLA-2α) on CE cells was evaluated by flow cytometry, RT-PCR, immunohistochemistry, or in situ hybridization. Anti-CTLA-2α neutralizing antibodies, CTLA-2α siRNA, or pro-cathepsin L blocking proteins were used to abolish the CE-inhibitory function.
Results: Cultured CE cells produced CTLA-2α on their surfaces, thereby enabling bystander CD4(+) T cells to be converted to Treg cells by TGFβ promotion. CE-induced Treg cells had immunosuppressive capacities by highly expressing CD25(high) and Foxp3. When mRNA downregulation (siRNA transfection), neutralizing antibodies, or blocking proteins were used to block CTLA-2α expression on CE cells, CE-induced Treg cells failed to acquire Treg function.
Conclusions: These findings indicate that cell surface CTLA-2α contributes to the CE-dependent suppression of bystander T cells. Thus, ocular resident tissue-exposed T cells can be induced to become regulators within the peripheral microenvironment.