Role of MICA antibodies in solid organ transplantation.

As a potential transplant antigen, major histocompatibility complex class I chain-related gene A (MICA) antigen, has attracted increased attention because of its possible role in solid organ transplantation. There are two MICA forms, and MICA antibodies and soluble MICA (sMICA) have been found in the serum of transplant recipients. We searched MEDLINE, EMBASE, and the Cochrane Library for original reports of clinical studies involving the effect of MICA on outcomes of renal, heart, lung, and liver transplantation. In addition to the human leukocyte antigen antigens, which elicit a strong immune response, the polymorphic MICA antigens induce production of MICA antibodies and sMICA. A number of clinical studies have shown that MICA antibodies correlate with an increased incidence of rejection and a decreased allograft survival rate following renal or heart transplantation. Although it is clearly associated with chronic rejection of lung allografts, no such correlation was found for liver transplantation. Moreover, sMICA showed a negative association with acute rejection (AR) and may be a good predictor of heart transplant outcomes. These data suggest MICA expression patterns and regulatory function may be tissue specific and that different transplants have different organ-specific outcomes.