Immunoregulation by aqueous humor

The eye is a classic example of an immune-privileged site. To investigate t he local defense system of the eye, the immunosuppressive effects of the aq ueous humor on cytokine production was examined. Methods. Using T cell clon es (TCCs) established from infiltrating cells in the aqueous humor of patie nts with human T lymphotropic virus type 1 (HTLV-1) uveitis as target cells and the aqueous humor of patients with senile cataract obtained during cat aract surgery, we examined the effects of the aqueous humor on the producti on of cytokines by HTLV-1-infected TCCs. Results. HTLV-1-infected TCCs prod uced large amounts of various cytokines. The aqueous humor inhibited the pr oduction of cytokines in a dose-dependent manner. The inhibitory activity w as heat labile. First protein liquid chromatography showed at least four ma jor peaks of different molecular size, indicating that the aqueous humor co ntains multiple immunosuppressive factors. Transforming growth factor-beta, alpha-melanocyte-stimulating hormone, and vasoactive intestinal peptide di d not suppress cytokine production. The inhibitory activity was neutralized by monoclonal antibody to Fas ligand. Conclusion. These data suggest that soluble Fas ligand is a candidate suppressive factor in the aqueous humor.