The blood transfusion effect: experimental aspects

In some animal models of organ transplantation, notably the rat, preoperative administration of donor strain blood may produce long-term allograft survival even in the absence of adjunctive immunosuppressive therapy. The ability of blood transfusion to prevent rejection is highly dependent on the strain combination and type of graft, as well as the nature, dose and timing of transfusion. Although the effect is donor-specific, partial sharing of MHC and/or minor antigens between the blood and organ donor may be sufficient to prolong graft survival. The mechanisms underlying the enhancing effect of blood transfusion and other protocols which lead to specific unresponsiveness in the adult animal are undoubtedly complex and still poorly understood. In contrast to neonatal tolerance, where there is complete clonal deletion or anergy, lymphocytes from enhanced animals often show normal alloreactivity in vitro. Blood transfusion provokes an accelerated immune response to an allograft with rapid leukocyte infiltration of the graft and associated induction of class I and class II MHC target antigens. Moreover, graft infiltrating cells obtained from non-rejecting grafts in transfused recipients show levels of in vitro specific cytotoxicity equivalent to or in excess of those found in rejecting grafts. Despite the heightened cellular response provoked by blood transfusion, host regulatory mechanisms override the rejection response and there is substantial evidence for the existence in transfused animals of T cells with antigen specific suppressor activity. However, the site in the rejection process at which suppression is mediated is unknown.(ABSTRACT TRUNCATED AT 250 WORDS)