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[L. rejectio, a throwing back]

1. Refusal to accept or to show affection. In animals, for example, the young may be ignored or driven away by their mother.
2. In tissue and organ transplantation, destruction of transplanted material at the cellular level by the host's immune mechanism. Transplant rejection is controlled primarily by T cells, but macrophages and B lymphocytes are also involved. Maintenance immunosuppressive therapy with cyclosporine, mycophenolate, and tacrolimus, which inhibit or block T-cell activity, lowers the risk of transplant organ rejection. Monoclonal and polyclonal antibody therapies are saved for acute rejection.

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