HLA Class II Antigens — Significance in Organ Transplantation

Abstract

The major and minor histocompatibility systems are primarily responsible for determining the fate of an organ graft when it is transplanted into an unmodified recipient. Incompatibility for major and/or minor histocompatibility antigens can result in graft rejection. The major histocompatibility antigens are coded by a gene complex - the major histocompatibility complex (MHC). The MHC genes and molecules are the best characterised of these two histocompatibility systems. A discussion of the MHC and its significance in transplantation will form the major part of this article, however it is important to point out that minor histocompatibility antigens also play a role in determining the survival of an allograft. Incompatibility for minor histocompatibility antigens only, in other words the situation that occurs when the donor and the recipient are identical or matched for all the MHC antigens, can result in graft rejection. The importance of minor antigens has been demonstrated using experimental systems, particularly in the mouse where these antigens have been best characterised (1, 2), but it has also been shown in clinical bone marrow transplantation. In the latter case immune responses against minor histocompatibility have been used to develop reagents for characterising minor antigens in man (3).