In order to study the immunological status of rats transplanted with H-1-compatible kidney allografts, LEW rats were grafted with F and (Fischer x Lewis)F1 (FLEWF1) kidneys. Most of the F kidneys were rejected within 55 days, only 4 of 24 surviving for more than 4 months. However, two-thirds of the FLEWF1 recipients survived for more than 4 months, the others having died within 64 days.
During the first postoperative week, high levels of serum lymphocytotoxic antibodies were found in recipients of F kidneys, and thereafter there was little change. In this respect these rats did not differ from recipients of kidneys with major histocompatibility differences. However, recipients of FLEWF1 kidneys had low haemagglutinating and lymphocytotoxic antibody titres.
No serum-blocking factor could be found in kidney of recipients by use of the microcytotoxicity assay (MCA) or inhibition of allorosette formation. Cellular immunity, which was studied by means of the graft-versus-host reaction (GVHR) and the microcytotoxicity assay, was detected in the first postoperative week. This immunity gradually declined, and after 6 weeks it was no longer detectable.
The immunological status of the long-term surviving kidney recipients remained unchanged, even when they were provided with further antigenic challenge in the form of two successive donor strain skin grafts.