In transplantation biology, the refusal by the body to accept transplanted cells, tissues or organs. For example, a kidney transplanted may be rejected.
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1. The immunologic response to incompatibility in a transplanted organ. 2. A refusal to accept, recognize, or grant; a denial. 3. Elimination of small ultrasonic echoes from display. [L. rejectio, a throwing back]
- accelerated r. a transplant r. manifested in less than 3 days.
- acute r. SYN: acute cellular r..
- acute cellular r. graft r. that usually begins within 10 days after a graft has been transplanted into a genetically dissimilar host. Lesions at the site of the graft characteristically are infiltrated with large numbers of lymphocytes and macrophages that cause tissue damage. See primary r.. SYN: acute r..
- allograft r. (al′lo-graft) the r. of tissue transplanted between two genetically different individuals of the same species. R. is caused by T lymphocytes responding to the foreign major histocompatibility complex of the graft.
- chronic r. a transplant r. occurring gradually, sometimes months later.
- chronic allograft r. immunologically mediated damage to the allograft, typically occurring months or years after transplantation.
- first-set r. allograft transplantation between two organisms not previously sensitized to the graft tissue. Necrosis of the graft usually begins within 10 days of transplantation.
- hyperacute r. 1. a r. that usually develops immediately after the implantation of a vascular graft; may be caused by preformed, cytotoxic antibodies to the graft; 2. a form of antibody-mediated, usually irreversible damage to a transplanted organ, particularly the kidney, manifested predominantly by diffuse thrombotic lesions, usually confined to the organ itself and only rarely disseminated.
- parental r. 1. withholding of affection from or denial of attention to one's child; 2. child's withholding of affection from its parent.
- primary r. a r. occurring more than 7 days after transplantation, mainly from a cellular immune response.
- second set r. an accelerated r. of a transplant that occurs when an individual has been previously sensitized to the graft.

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re·jec·tion ri-'jek-shən n
1) the action of rejecting or the state of being rejected <feelings of \rejection> <\rejection of the atypical child by (G. S. Speer)>
2) an immune response in which foreign tissue (as of a skin graft or transplanted organ) is attacked by immune system components (as antibodies, T cells, and macrophages) of the recipient organism

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(in transplantation) the destruction by immune mechanisms of a tissue grafted from another individual. Antibodies, complement, clotting factors, and platelets are involved in the failure of the graft to survive. allograft rejection is a vigorous response that can be modified by drugs (such as ciclosporin and corticosteroids) and antibodies against T-cells; xenograft rejection is an acute response that is at present beyond therapeutic control.

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re·jec·tion (re-jekґshən) an immune response against grafted tissue that may result in failure of the graft to survive; called also graft r.

Medical dictionary. 2011.

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