Mixed leucocyte culture blocking factor activity in allograft recipients and its role in the clinical outcome of human cadaveric renal allografts.

Seventeen renal allograft recipients were followed serially both pre- and post-transplantation for the presence of mixed leucocyte culture blocking factor activity (MLC-BFA) in their plasma. Patients could be divided into three distinct groups on the basis of MLC-BFA and lymphocytotoxin (LT) determinations. Fifteen out of seventeen patients possessed MLC-BFA at one time or another while four out of seventeen were positive for LT. Four patients of group 1 with pre-transplant LT and MLC-BFA rejected their grafts within 1 year. Two LT negative patients of group 2 developed no detectable MLC-BFA during a follow-up period of over 1 year. One other patient developed MLC-BFA 8 months following transplantation. All three patients had an excellent clinical course. Ten patients belonging to group 3 possessed no LT or MLC-BFA prior to transplantation but developed MLC-BFA alone after receiving an allograft. Only one patient rejected his allograft within 2 months. The remaining nine patients experienced mild rejection crises during the first 3 months after transplantation but had excellent renal function at 1 year or beyond that time. Our results indicate that MLC-BFA in the presence of LT may not prevent rejection. MLC-BFA is associated with a good clinical course in LT negative patients. However, certain patients who fail to develop LT or MLC-BFA in spite of repeated blood transfusions prior to transplantation may also do extremely well in the absence of detectible MLC-BFA.