Tissue-specific and tissue-restricted histocompatibility antigens

Strictly defined, tissue-specific antigens are antigens characteristic of one particular tissue or cell. They are usually associated with autoimmunity and are remarkably homologous between species. In contrast, histocompatibility (H) antigens reflect polymorphism within species - they are alloantigens - and class-I major H complex (MHC) antigens - at least mouse H-2D and H-2 K and human HLA-A and -B, the commonest targets of acute allograft rejection - are widely distributed in the body; class-II MHC antigens - mouse Ia and human DR - have a much more limited distribution, being expressed primarily on B lymphocytes and on macrophages and other cells involved in antigen presentation and immune activation. This review is devoted to H antigens other than class-IIMHC antigens with limited if not highly specific, tissue distribution. Some of these antigens are classic tissue-specific antigens, others are alloantigens with limited tissue expression. Much of the evidence that they evoke immune responses that damage or destroy transplanted tissue is incomplete or circumstantial, but some is convincing and includes the immunogenetic characterization of new antigen systems that may have to be reckoned with clinically, especially when dealing with HLA-matched transplants.