Immunosuppressive factors in porcine ciliary body.

Immunosuppressive factors locally present in the anterior tissues such as the ciliary body may contribute to the immunological privilege of the anterior chamber of the eye. Porcine ciliary body extracts contain at least three immunosuppressive factors (greater than 200 kDa, 25 kDa and 2.5 kDa) which can be separated by Sephacryl S300 gel filtration. On the basis of its molecular weight and reversal of inhibitory activity by anti-transforming growth factor beta (TGF beta) antibody, 25 kDa factor is identified with TGF beta. The high molecular factor is low in protein content and its activity is not affected by anti-TGF beta antibody. The 2.5 kDa factor is most likely to be identical with a low molecular factor present in the vitreous body and aqueous humor. This low molecular factor is extracted from nonpigmented ciliary epithelial cells but seems to be absent in the extracts of pigmented epithelial cells. The regional distribution suggests that the factor may be synthesized and secreted with the aqueous humor by the nonpigmented cells. All three factors suppress lymphoblastogenesis without affecting the expression of CD4 and CD8. Identical or similar factors may be present in other immunologically privileged tissues and be responsible for maintaining the immunologically suppressed environment.