Intrasplenic liver parenchymal cells in conjunction with low-dose rapamycin and cyclosporine induce a unique and specific prolongation of rat cardiac and small bowel allograft survival.

Abstract

These experiments investigated the immunosuppressive properties of liver tissue. Brown Norway (BN; RT1n) rat heart allografts survived in untreated control Wistar Furth (WFu; RTl(u)) rat recipients for 6.2 +/- 1.5 days, while allografts in animals that received rapamycin (RAPA) 0.0075 mg/kg/day and cyclosporine (CsA) 0.375 mg/kg/day delivered for 14 days by continuous intravenous infusion (civi) using osmotic pumps in conjunction with intrasplenic (i.s.) saline survived to 18.4 +/- 1.3 days. i.s. addition of 3 M-KCl extracted BN hepatic antigen or unpurified BN hepatocytes (liver parenchymal cells-5 x 10(7)/kg), which exhibited a 4.8% class II antigen expression, and which alone failed to prolong allograft survival (MST = 6.0 +/- 1.4 days), increased heart allograft survival to 25.3 +/- 2.3 and 27.2 +/- 1.9 days, respectively (p < 0.01). Hepatocyte purification using Dynabeads and Percoll reduced class II expression to 0.9% and increased allograft survival to 32.8 +/- 1.6 days (p < 0.01). In contrast, the effect of 5 x 10(8)/kg BN erythrocytes, exhibiting only 0.1% class II expression, was much less (23.8 +/- 1.9 days). Administration i.s. of BN splenocytes or nonparenchymal liver cells, demonstrated by flow cytometry to exhibit a 47.3 or 55.1% expression of class II antigen, respectively, failed to induce any significant increase in allograft survival (18.4 +/- 4.6 and 19.4 +/- 0.5 days, respectively). Survival of BN rat small bowel allografts was increased in Lewis (LEW; RTl1) rat recipients treated with RAPA, CsA, and unfractionated BN hepatocytes from 10.2 +/- 1.9 to 21.2 +/- 1.5 days. Pretreatment with i.s. BN hepatocytes, 14 days prior to harvesting, reduced WFu lymphocyte responses to allogeneic stimulation with BN or ACI spleen cells by 75 and 70%, respectively. Addition of 1 x 10(5) unpurified donor-specific BN or third-party Buffalo (BUF; RTl(b)) hepatocytes, but not supernatant, to the responder wells of MLCs resulted in a 61 and 40% suppression, respectively, of the WFu lymphocyte response induced by BN allogeneic stimulation. These findings suggest that while class I MHC expression has a significant role to play in exerting the immunosuppressive effects of hepatocytes, other influences more specific to liver may also prevail.