Fetal pig pancreas xenograft rejection is associated with selective chemokine and chemokine receptor profiles which are suppresed by CTLA4-Fc and anti-CD40L treatment
Introduction Fetal pig pancreas (FPP) xenograft rejection is characterized by a temporal pattern of graft macrophage and CD4 T cell infiltration. Mechanisms of effector cell recruitment remain unclear and chemokines may play a role. We have performed a time course study of chemokine and chemokine receptor gene expression in a model of FPP xenograft rejection and examined the corresponding cellular infiltration, before and after short-term costimulation blockade.
Materials and methods FPP fragments were transplanted under the renal capsule of C57B1/6 mice. Islet isografts were controls for the surgical procedure. Treatment animals received CTLA-4Fc (500 μg day 2) and anti-CD40L (500 μg day 0, 2, 4 and 6). Grafts were harvested for mRNA and histological analyses. Multi-probe ribonuclease protection assays (RPA) were used to examine intragraft gene expression of 9 chemokines and 6 chemokine receptors. Confocal laser microscopy was used to examine intragraft cell infiltration and RANTES protein staining.
Results Rejecting xenografts showed enhanced expression of MIP-1B on day 2 corresponding with initial macrophage appearance, and MIP-1B, MCP-1, RANTES, IP-10, and lymphotactin on day 4 corresponding with initial CD4 T cell appearance and further macrophage accumulation. Initial RANTES protein appearance coincided with mRNA expression in xenografts. Chemokine receptor expression was consistent with the ligand profile with CCR1, CCR2, and CCR5 up-regulated on days 2 and 4, and CCR2 was also enhanced on day 6. Eotaxin, MIP-1A, MIP-2, TCA-3, and CCR1b, CCR3 and CCR4 expression was not elevated. This chemokine/receptor data was consistent with a Th 1 type response. Costimulation blockade resulted in 100% graft survival at 100 days and was associated with suppression of the early chemokine gene expression at day 4 seen in rejecting grafts, together with a reduction in early inflammatory cell infiltrate.
Conclusions This chemokine and receptor expression profile was consistent with the temporal appearance of macrophages and CD4 T cells. Short-term costimulation blockade resulted in indefinite FPP survival and was associated with abrogation of the early chemokine gene response suggesting these molecules are important mediators of the leukocyte infiltrate in FPP xenograft rejection.