CHARACTERISTICS OF B LYMPHOCYTE AND NK CELL TOLERANCE IN A HAMSTER-TO-ATHYMIC NUDE RAT CARDIAC XENOTRANSPLANTATION MODEL

Abstract

468 Aims: In a hamster-to-nude rat heart transplantation(Tx) model, T-independent xenogeneic tolerance has recently been induced by our group. Here some characteristics of the B cell and natural killer(NK) cell tolerance involved are further explored. Methods: The tolerance induction protocol consisted of: i)injection of a minced hamster heart suspension and a depleting anti-NK serum (1mg anti-asialo GM-1 iv) on d-14; ii)a 4-week(d-14 to d+14) administration of leflunomide (LEF, 20mg/Kg/d by gavage); iii)abdominal or cervical heterotopic hamster heart Tx on d 0. Group 1 received the aforementioned protocol(n=18). Group 2 received the same protocol except that no hamster heart Tx was performed on d 0 (n=4) and was utilized to study the reversibility of NK and B cell tolerance when no transplant was present. Group 3 was utilized to investigate the interruption of B cell and NK cell tolerance and received in addition to the group 2 regimen, a hamster heart Tx or 50×106 hamster spleen cells i.p. on d+7, +15, +30, +60, respectively. Results: Hamster antigen infusion together with a 4-week administration of LEF was sufficient to tolerize B cells. This T-independent xenogeneic B cell tolerance to hamster antigens was cross-tolerant to mouse antigens but not to guinea pig antigens. Even in the absence of a graft(group 2), the B cell tolerance persisted for at least 45 days after withdrawal of LEF. Within this period, neither injection of hamster spleen cells nor Tx of a hamster heart could provoke detectable anti-hamster antibodies in the serum nor their deposition within transplanted grafts(group 3). By contrast, the NK cell tolerance was more species-specific, because tolerant NK cells displayed normal killing of YAC-1 cells and third party mouse con-A lymphoblasts, but no lysis of donor hamster con-A lymphoblasts. Maintenance of NK cell tolerance was dependent upon the presence of a hamster heart graft. Otherwise, NK cytotoxicity recovered within two weeks. Consistent with this, rejection occurred 3 to 4 days and was characterized by a dense infiltration of NK cells after donor heart Tx in group 3 rats on d+15, +30, and +60, respectively. Furthermore, the NK cell tolerance seemed not to be based on deletion, because IL-2 activated NK cells from tolerant rats showed normal lysis of hamster con-A lymphoblasts. Conclusions: T-independent xenogeneic B cell tolerance is long-lasting, even in the absence of a graft. On the contrary, xenogeneic NK cell tolerance is short-lasting, dependent upon the presence of a graft and is reversible by adding IL-2 in vitro.