OBJECTIVETo review the role of polymorphism of major histocompatibility complex class I-related chain A (MICA) gene and antibodies against MICA antigens in transplant immunology.

DATA SOURCESThe data used in this review were mainly from our own results and from the relevant English language literatures published from 1999 to 2010. Some data presented in this review are in press.

STUDY SELECTIONArticles regarding MICA gene discovery and pioneering finding of antibodies against MICA antigen and allograft rejection were selected. This review chronicles the development of our understanding of the role that MICA antigens and antibodies may play in organ transplantation.

RESULTSPolymorphic glycoprotein MICA antigens were detected on freshly isolated human umbilical cord endothelial cells, but not on peripheral lymphocytes. Antibodies were found and typing of recipients and donors by sequencing the MICA alleles has established that de novo antibodies produced in kidney transplant recipients are directed at mismatched MICA epitopes and are associated with acute rejection and chronic transplant failure. The specificity of antibodies against the epitopes of MICA antigens were well characterized by donor MICA typing, single antigen array testing with antibody absorption and elution. Acute graft-versus-host disease was observed in stem-cell recipients who were mismatched for MICA.

CONCLUSIONSImmunization against mismatched MICA epitopes encountered in donor organs after transplantation may result in antibodies against MICA alleles. Testing for MICA donor-specific antibodies (DSA) which are associated with early failure of kidney transplants may be helpful for identifying some of the targets of antibodies against antigens other than the human leukocyte antigen (HLA) and for improving transplantation outcome.