IL-2 + INTERFERON-?? DOUBLE KNOCKOUT MICE REJECT HETEROTOPIC CARDIAC ALLOGRAFTS

Abstract

391 Several recent studies have suggested that MHC mismatched allografts can undergo rejection by either a Th1 and Th2 biased immune response. This observation, however, has not been confirmed in an experimental system definitely lacking expression of the major Th1 cytokines interleukin-2 (IL-2) and interferon-gamma (IFN-γ). Therefore, we have interbred two mouse strains, each bearing a single targeted gene disruption for IL-2 or IFN-γ to obtain double gene knockout mice (DKO) and control animals(WT, IL-2 KO, IFN-γ KO) on the same genetic background (C57BL/6 × 129; H-2b). Young DKO mice are healthy, have undiminished delayed type hypersensitivity responses, and exhibit a shift in IgG/IgG2a isotype ratio characteristic of Th2 deviation. We tested the hypothesis that a lack of both IL-2 and IFN-γ expression will not prevent allograft rejection by performing heterotopic cardiac allografts from DBA/2j (H-2d) donors into untreated 6-8 week old WT, IL-2 KO, IFN-γ KO, and DKO mice (C57BL/6× 129; H-2b). Control allografts used C57BL/6 × 129 F1 donors. Graft survival was assessed by palpation.TableResults: DKO mice rejected heterotopic cardiac allografts slightly faster than the IL-2 single KO mice (p<0.05), and significantly faster than IL-2 KO and IFN-γ KO mice (p<0.01). These results were analogous to those found in our control groups, where IFN-γ KO mice rejected allografts slightly faster than WT controls. Histologic analysis of the rejecting grafts showed extensive lymphocyte infiltration in the DKO grafts. Allografts from IFN-γ KO and DKO mice showed evidence of infarction as well. We are presently analyzing multiple gene expression events by RT-PCR. Conclusions: The combined absence of IL-2 and IFN-γ is insufficient to prevent rejection of heterotopic cardiac allografts.