DIFFERENT MECHANISMS OF PROLONGED ALLOGRAFT SURVIVAL INDUCED BY ANTI-DONOR CLASS II ANTIBODIES OR DONOR SPECIFIC TRANSFUSION

Abstract

273 Allograft tolerance can be induced in the LEW.1W to LEW.1A strain combination by donor specific blood transfusion (DST) prior to grafting. We have previously shown that this state of tolerance is characterized by an inhibition of Th1 and Th2 related cytokines and is correlates with an early, and high production of TGFβ1 by graft infiltrating cells (GIC) (J. Clin. Invest. 102:1920, 1998). A potentially regulatory CD8+ T cell clone with a public Vβ18-Dβ1-Jβ2.7 rearrangement was found, from day one, in GIC from DST treated recipients (J. Immunol. 157: 1250, 1996). The study of alloantibodies in sera from DST treated recipients showed a decrease in anti-donor class I alloantibodies with an increase in anti-class II responses, suggesting a role for these alloantibodies in the induction of tolerance (Eur.J Immunol. 24:1627, 1994). Thus, it could be interesting to compare the immune response following the injection of anti-class II serum to those following DST induced tolerance. Anti LEW.1W sera prepared from LEW.1A recipients after LEW.1W skin graft and cell immunizations was depleted of anti-class I alloantibodies by absorption into LEW.1W platelets and administered on day 0 (0.5 ml IV) to LEW.1A recipients receiving either a heart or kidney allograft from LEW.1W donors. This treatment prolongs heart allograft survival (41+/−16 days, n=8 compared to 6.75+/−0.25 days, n=6 in controls, p<0.001). Three heart allografts survived for more than two months and with the same treatment, kidney allografts survived indefinitely. Cellular infiltrate, Vβ usage patterns and the level of cytokine transcripts (as measured by competitive RT-PCR) were analysed 5 days after transplantation in grafts from anticlass II injected recipients and compared with control grafts and grafts from DST tolerant recipients. No Vβ18 clonotypic gene rearrangement was found in any of the grafts stimulated with anti-class II sera. No increase in TGFβ mRNA accumulation was seen when compared to controls, which contrasted with the results seen for allografts tolerized DST treated animals. The leucocyte infiltrate, which consisted predominantly of macrophages (60%) and T lymphocytes (20%), was significantly decreased in grafts from anti class II injected rats, as compared to controls and grafts from DST treated recipients. Taken together, these results suggest that the mechanism of tolerance induction in these two models, previously described as «active» and «passive» enhancement, are different and that DST tolerance induction did not occur only via induction of anti-class II.