Background: Major histocompatibility complex-mismatched Lewis rate cardiac grafts (inferior vena cava drained) are promptly rejected by Buffalo recipients (mean survival time, 7 days). Ultraviolet-B (UVB) irradiation modulates donor immunogenicity and down-regulates in vitro immune responses. We found that Buffalo recipients (BUF; RT1b) preimmunized with 2.5 x 10(7) nontreated Lewis spleen cells (LEW; RT1(1)) by portal venous (PV) injection 7 days before a portal vein-drained heterotopic graft of LEW heart resulted in only 20% surviving long-term (n = 10) (naive rats rejected a cardiac allograft drained into the portal vein in mean survival time of 13.5 days [n = 5]). In contrast, BUF recipients receiving PV injection of UVB-treated LEW spleen cells permitted 70.6% indefinite allograft survival (n = 34) with a mean survival time of greater than 150 days.
Methods: These studies examined the effect of untreated or UVB-irradiated donor spleen cells administered intraportally on the recipient's cell-mediated responsiveness as serially measured by the mixed lymphocyte culture and limiting dilution analysis of T-helper precursors (pTH) and cytotoxic precursors (pCTL). Survival of heterotopic cardiac allografts transplanted with PV drainage at various intervals after PV alloantigen administration were correlated with changes in these in vitro studies.
Results: The precursor frequencies in the spleens of BUF recipients given nontreated LEW spleen cells intraportally 7 days previously were 1/16,170 (pTH) and 1/11,929 (pCTL), whereas those in the spleen of BUF recipients receiving UVB-treated LEW spleen cells decreased to 1/152,409 pTH and < 1/5 X 10(5) pCTL. These hyporesponsive BUF spleen cells responded normally to the third-party alloantigen, irradiated ACI spleen cells (RT1 alpha), with mixed lymphocyte culture tritiated incorporation of 133,220 cpm (control, 123,276 cpm), 1/13,364 pTH (control, 1/13,541), and 1/71,156 pCTL (control, 1/73,985), indicating that the hyporesponsiveness induced by UVB-treated donor spleen cells is antigen specific. The recovery of in vitro responsiveness correlates with decreasing cardiac graft survival to normal rejection times by 200 days after portal vein antigen administration. When 100 units/ml exogenous recombinant interleukin-2 (rIL-2), but not rIL-1 or rIL-4, was added to cultures, the hyporesponsiveness of spleen cells recovered to normal levels with tritiated incorporation of 201,227 cpm and pTH frequency of 1/32,227, suggesting that the hyporesponsiveness to donor antigen is due to anergized T-helper lymphocytes and not to clonal deletion.
Conclusions: By administering properly modified alloantigen into the hepatic environment by portal vein inoculation, prolonged T-cell anergy can be induced, which allows the indefinite acceptance of donor-specific heterotopic cardiac allografts.