Immunological characteristics of amniotic epithelium.

We review recent experimental evidence of the immunosuppressive and immunogenic potential of amniotic epithelial cells. Since cryopreserved amniotic membrane (AM) has been used in clinical applications, much research has focused on the beneficial effects of amniotic stromal matrix rather than on the function of viable amniotic cells. However, viable human amniotic epithelial cells (HAECs) have been shown to elicit beneficial effects on secretion of anti-inflammatory factors. Topical application of culture supernatant from HAECs leads to profound suppression of suture-induced neovascularization in cornea and fewer major histocompatibility complex (MHC) class II antigen-presenting cells (APCs) in inflamed cornea after thermal cautery. Furthermore, expression of interleukin (IL)-1beta mRNA was suppressed in cauterized cornea. These results suggest that HAECs are a source of soluble anti-inflammatory factors that suppress corneal inflammation. However, viable amniotic epithelial cells display antigenicity and immunogenicity as allografts. Fresh allogeneic amniotic epithelium (AE) expresses MHC class I antigens and sensitizes recipients when placed in the eye, although long-term memory of allo-specific delayed hypersensitivity (DH) was not acquired. Allogeneic AE was clearly vulnerable to acute immune rejection in specifically sensitized recipients and recipients of repeated AE transplantation. We therefore suggest that immunogenicity of AE should not be ignored, and use of AM from different donor placentas should be emphasized when repeated AM transplantation is required in patients clinically.