Immunological pathways of rejection in sensitized recipients.

In allotransplantation the common causes of sensitization are blood transfusion, pregnancy and rejection of an allograft. An additional route of sensitization that should not be overlooked is the potential crossreactivity of T cells responding to enviromental antigens or pathogens that may be able to cross react with alloantigens expressed by the antigen presenting cells (APC) within an organ graft. In this situation the T cells of the host would be sensitized to the alloantigens of the organ donor even though the donor alloantigens themselves had not been encountered previously. The frequency of crossreactive T cells present in a recipient and their contribution to the rejection of allografts is extremely difficult to assess with the tools currently available. [ABSTRACT FROM AUTHOR]