Relationship between the Decrease of Cytotoxic Antibody with the Elapse of Time and Hyperacute Rejection in Hyperimmunized Rats

Preformed cytotoxic antibody which causes hyperacute rejection is formed on gestation, blood transfusion and infection. It is an important problem whether or not transplantation is possible in the recipients sensitized like this.
We studied the decrease of preformed cytotoxic antibody with the elapse of time in sensitized recipients and its influence on graft survival time, using inbred rats.
Inbred ACI rats and Fischer rats were used as experimental models. Hyperimmunized Fischer rat recipients were prepared by skin grafting and spleen lymphoid cell booster. In order to observe the course of decrease or disappearance of the antibody after sensitization, anti T cell warm cytotoxic antibody (CA-TW) was assayed in rat groups which were hyperimmunized one week, one, three and six months before, respectively. The hearts of ACI rats were transplanted to the groups of hyperimmunized Fischer rat recipients to study the relationship between graft survival time and cytotoxic antibody.
1. Controls: The heart of ACI rat transplanted to nontreated Fischer recipient showed graft survival time of 8.1 ± 1.4 days.
2. Group of rats hyperimmunized one week before: The transplanted ACI heart was hyperacutely rejected 0.55 ± 0.38 hr after grafting in all recipients.
3. Group of rats hyperimmunized one month before: The transplanted ACI heart was hyperacutely rejected in five of the 12 recipients. The graft survival time was 17.2 ± 9.2 hr.
4. Group of rats hyperimmunized three months before: Hyperacute rejection was observed in three of the 12 recipients. The graft survival time was 43.0 ± 28.1 hr.
5. Group of rats hyperimmunized six months before: Hyperacute rejection was not observed. The graft survival time of the transplanted heart was 96.0 ± 37.5 hr. The pattern of rejection varied from accelerate to acute rejection.
6. Spontaneous decrease of preformed cytotoxic antibody after hyperimmunization: Fischer rats were hyperimmunized by skin grafting from ACI rat and five booster shots of spleen lymphoid cell. The change of their antibody titer was examined.
CA-TW of the groups hyperimmunized three and six months before, respectively were significantly lower than that for the group hyperimmunized one week before the transplantation.
7. Relationship between preformed cytotoxic antibody titer and graft survival time of transplanted heart: There was a negative correlation between CA-TW titer and graft survival time; r = —0.7274.
To sum up, cytotoxic antibody generated by hyperimmunization was decreased with the passage of time. It was thought that the decrease of CA-TW closely related to graft survival time. It was revealed that hyperacute rejection no longer occurred after a lapse of six months after sensitization and that the graft was taken for more than 90 hr and then rejected either by accelerate or by acute rejection.