The role of naturally produced antibody in discordant xenograft rejection is still uncertain. Twelve orthotopic pig-to-baboon heart transplants (HTx) were performed. In 2 baboons, no antibody adsorption (AbA) was performed. In 5 baboons, AbA with a pig lung was performed during circulatory arrest. In 5 baboons, AbA and blood exsanguination at the beginning of cardiopulmonary bypass (CPB) were performed. Baboons were divided into 2 groups; group 1 (n=4) died within 24 hr of HTx and group 2 (n=8) survived more than 24 hr. Mean survival period was 9.8+/-3.0 hr in group 1 and 151+/-33 hr in group 2. Baboon anti-pig antibody (Ab) was measured before CPB, before circulatory arrest, during AbA, at the end of CPB, and daily after HTx. Anti-RBC Ab was measured by the titration method at temperatures of 4-degrees-C and 37-degrees-C (RAb-4 and RAb-37). Anti-endothelial cell Ab (EAb) and anti-white blood cell Ab (WAb) titers were measured with ELISA. RAb titration greater-than-or-equal-to 1/4 and EAB and WAb greater-than-or-equal-to 1/256 were determined to be seropositive (S(+)). S(+) rate of RAb-37 at the end of CPB (endCPB) in group 2 was significantly higher than that in group 1 (8/8 vs. 1/4; P<0.05). The seronegative (S(-)) rates of RBC-4 and EAb (end-CPB) in group 2 were higher than those in group 1 (7/8 vs. 1/4 and 6/8 vs. 1/4, respectively), but not significantly. There was no difference in S(-) rate of WAb (endCPB) between group 1 and group 2. More than 4-fold decrease in RAb-4 and RAb-37 by AbA with a pig lung was observed in 5 and 7 of 8 baboons, while EAb and WAb did not change by AbA. In all of group 2, RAb-4 reverted to S(+) within 3 days after HTx. One baboon had no rejection episode and died of infectiOn 16 days after HTx (baboon 16); however, it also became S(+) for RAb-4 a day after HTx until death. In 4 of group 2, RAb-37 became S(+) 1 or 2 days before death by rejection. Baboon 16, however, became S(+) for RAb-37 7 days after HTx and S(-) again 9 days after HTx until death. EAb became S(+) in all of group 2, but 5 of them survived more than 5 days after seroconversion. It was concluded that a pig lung absorbed RAb-4 and RAb-37 but not EAb or WAb, and that RAb, especially RAb-37, may play a role in discordant xenograft rejection.
