Specific aqueous humor factors induce activation of regulatory T cells

To examine the possibility that aqueous humor-induced regulatory T cells could function in vivo, these T cells were examined for their ability to suppress adoptive transfer of delayed-type hypersensitivity (DTH). To begin to understand the mechanisms by which aqueous humor induces activation of regulatory T cells, alpha-melanocyte stimulating hormone (MSH) and transforming growth factor (TGF)-beta2 were examined for ability to induce regulatory T cells.

Primed T cells were treated with aqueous humor and assayed for regulatory activity by injecting them intravenously along with DTH-mediating T cells into syngeneic mice. Antigen-pulsed antigen-presenting cells (APCs) were injected into the pinna of the mouse ear, and swelling was measured 24 hours later. Primed T cells were also activated in vitro in the presence of alpha-MSH, TGF-beta1, or TGF-beta2 and were assayed for proliferation and TGF-beta production along with suppressing DTH.

Aqueous humor-treated T cells suppressed inflammation mediated by DTH T cells. Maximum regulatory T cell activity was induced when primed T cells were activated in vitro in the presence of alpha-MSH followed 4 hours later with active TGF-beta2. Such T cells proliferated, produced TGF-beta, and suppressed DTH, suggesting that alpha-MSH and TGF-beta2 induce activation of regulatory T cells. No regulatory T cell activity could be induced in the presence of TGF-beta1.

The ocular microenvironment constitutively produces immunoregulatory factors that suppress the induction of inflammatory activity and promotes regulatory T cell activity. Such regulatory T cells can further contribute to maintaining the normal immunosuppressive ocular microenvironment through their ability to suppress activation of other inflammatory T cells.