MICA: a secondary histocompatibility molecule playing a role in the rejection and immunotolerance

Abstract

The Major Histocompatibility Complex class I chain-related genes A – MICA – encodes molecules structurally similar to the HLA class-I. The major difference is the lack of β2-microglobuline and peptide-binding. They are expressed on the membrane of the fibroblasts, endothelial, epithelial and tumor cells. The MICA transcription is induced by cellular stress. These molecules interact with NKG2D receptors expressed by NK cells and Tγδ and Tαβ-CD8+ lymphocytes, inducing cytotoxicity. The MICA system is polymorphic, and the molecules have been shown to be important in tissue and organ transplants, inducing the production of alloantibodies and graft rejection, regardless the HLA-antibodies. Recently, it has been demonstrated that the soluble MICA molecules (sMICA) are involved in the evasion of the immune response under tumoral and pregnancy conditions. This paper describes the MICA biology, pre- and post-transplant anti- MICA antibodies, and also discussing the immunotolerance induction by the sMICA molecules.