Infectious tolerance develops after the spontaneous acceptance of Lewis-to-Dark Agouti rat liver transplants

Background. After monoclonal antibody or donor-specific transfusion treatment, infectious tolerance to rat or mouse heart or skin transplants can be passed on to naive recipients by adoptive transfer of tolerant lymphocytes. We examined whether similar regulatory cells develop after the spontaneous acceptance of Lewis-to-Dark Agouti (DA) rat liver transplants without immunomodulating agents. Methods. After Lewis-to-DA rat liver transplantation, 100 X 106 splenocytes were harvested and adoptively transferred into a 450 rad-irradiated naive DA rat 24 hours before Lewis heart transplantation. Adoptive transfer of CD4+ or CD8+ T cells was also examined. In some experiments, splenocytes from recipients with long-term accepted Lewis hearts induced by adoptive transfer were serially transferred to multiple generations of recipients before Lewis rat heart transplantation. In vitro mixed lymphocyte culture response and cytotoxic T lymphocyte generation were measured. Results. When splenocytes from a DA rat recipient > 60 days after Lewis rat liver acceptance were transferred into irradiated DA rat recipients, all Lewis rat hearts were accepted, whereas third-party Brown-Norway rat hearts were rejected. However, splenocytes from DA rat recipients 30 days after liver transplantation did not prolong Lewis rat heart survival. Adoptive transfer of 40 x 10(6) CD4+, 10 x 10(6) CD4+ or 10 x 10(6) CD8+ cells from a DA rat hearing Lewis rat liver >60 days resulted in acceptance of 88 %, 80 %, or 57 % acceptance of Lewis rat hearts, respectively. Serial second and third adoptive transfer of long-term survivor splenocytes resulted in the acceptance of all Lewis rat hearts. In mixed lymphocyte culture, splenocytes from a naive DA rat and a DA rat accepting a Lewis rat liver transplant for > 60 days showed similar proliferative responses to both Lewis and Brown-Norway rat stimulators. An equivalent level of indirect cytotoxic T lymphocyte activity was exhibited by splenocytes from both a naive DA and a DA rat accepting a Lewis rat liver transplant for >60 days. Conclusion. Regulatory cells developing after the spontaneous acceptance of a Lewis to DA liver transplant can serially adoptively transfer the acceptance of a Lewis rat cardiac graft in spite of the presence of in vitro antidonor reactivity. Both CD4+ and CD8+ populations have this regulatory activity, although the CD4+ population plays the dominant role.