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Any of numerous cell-surface antigens, such as the human leukocyte antigens, that identify a cell as self or nonself and determine whether a tissue graft will be accepted by a transplant recipient.
(Biochemistry) a molecule occurring on the surface of tissue cells that can take several different forms. The differences between histocompatibility antigens are inherited and determine organ transplant rejection
any antigen on the surface of tissue or blood cells that provokes an immune response and subsequent rejection of the tissue or cell when transplanted to an individual of a different antigenic type.