Identification of MICA as a new polymorphic alloantigen recognized by antibodies in sera of organ transplant recipients

MHC class I-related chain A (MICA) is an HLA-related, polymorphic gene the product of which may be recognized by a subpopulation of intestinal gamma d elta T cells and may play a role in the activation of a subpopulation of na tural killer cells. Using anti-MICA specific rabbit sera we previously demo nstrated chat freshly isolated monocytes, keratinocytes, fibroblasts, and e ndothelial cells express MICA. To analyze whet her MICA may be a target for specific antibodies in sera of transplanted patients, we produced three re combinant: MICA proteins consisting of the alpha1, alpha2, and alpha3 domai ns, and used them in an enzyme-linked immunosorbent assay. We found that se veral patients had specific antibodies against MICA. Most of them were dete cted in serum samples collected at different rimes after organ rejection. A lthough this finding raises the question of how these patients became immun ized, the fact chat the polymorphic, HLA-like MICA molecule, expressed at t he cell surface of endothelial cells, is recognized by specific antibodies in sera of transplanted patients, suggests the MICA may be a target molecul e in allograft rejection. Human Immunology 61, 917-924 (2000). (C) American Society for Histocompatibility and Immunogenetics, 2000. Published by Else vier Science Inc.