Immunophenotyping fish-to-mouse islet xenograft rejection: a time course study.

Tilapia islets, Brockmann bodies (BBs), transplanted under the kidney capsule (KC) of diabetic nude mice provide long-term normoglycemia, but, when transplanted into euthymic mice, reject in about one week. OBJECTIVES: The present study characterizes the cellular infiltrates at several time points during the xenograft rejection process. METHODS: Tilapia BBs were harvested, fragmented, cultured overnight, and then transplanted under the KC of streptozotocin-diabetic Balb/c mice. Glucose levels were measured daily until the mice were killed at 1 (n = 2), 2 (n = 2), 3 (n = 3), and 5 days (n = 3) post transplantation and at the time of BB graft rejection (n = 6). Serial frozen sections of graft-bearing kidneys were stained for murine macrophages (MOMA-2, F4/80, M170), CD4+ (L3T4) T-cells (YTS 191.1), and CD8+ (Ly-2) T-cells (YTS 169.4) by indirect immunoperoxidase; the presence of granulocytes and plasma cells was assessed with H&E stained sections. RESULTS: At 1 day, the grafts have undergone some central necrosis with macrophage infiltration. By 2 days, these changes are very well-developed and granulocytes, almost exclusively eosinophils, begin to surround the graft. At 3 days, rare CD4+ and CD8+ T-cells are seen at the graft kidney interface. Macrophages massively infiltrate the necrotic foci and pepper the graft. At 5 days and at rejection, macrophages and eosinophils predominated in the center of rejecting grafts while CD8+ T-cells and CD4+ T-cells were present at the periphery. Plasma cells were rare. CONCLUSION: We conclude that cell-mediated processes and eosinophils play roles in the rejection of cellular xenografts across this very wide phylogenetic barrier.