Serology of liver transplantation in the rat. I. Alloantibody responses and evidence for tolerance in a nonrejector combination.

The antibody response against class I and class II RT1 antigens has been studied in PVG rats grafted with DA liver. In this nonrejector combination, liver grafts survive permanently in all normal recipients and in about 50% of recipients presensitized by a DA skin graft, with concurrent induction of transplant tolerance for other DA organs and skin. Using a two-stage radioimmunoassay, the anti-class I (RT1Aa) levels in sera of normal PVG recipients of DA liver grafts were found to be low (maximal titer 1:50 serum dilution or less); after peaking at 2 weeks posttransplantation, they diminished to background levels by 6 weeks. The anti-RT1Aa response showed a close parallel to cell-mediated rejection events in the liver graft recipients. In contrast, anti-class II (RT1Ba/Da) responses reached much higher titers (over 1:1000), which were maintained for several weeks before declining after 4 months. Similar observations were made in presensitized recipients. The induction of tolerance in the alloantibody response was indicated by the inability of DA skin grafts to restimulate anti-RT1 antibody in liver recipients. The observations support the picture of "split tolerance" indicated by previous cellular studies in this combination.