High gelatinase activity in the engraftment area after islet transplantation. (A-B) Confocal images of tissue cryosections of islet grafts 4 days after transplantation to mouse abdominal muscle. (C-D) Islet grafts 14 days after transplantation. The sections were incubated at 37°C with quenched FITC-gelatin. Grafts are outlined by dashed lines. (A) Higher fluorescence intensity in islets engrafted in a wild-type muscle demonstrating high gelatinase activity cleaving the quenched gelatin, emitting absorbed light. (B) Low fluorescence intensity in islets engrafted in an MMP-9^−/− mouse. (C-D) The fluorescence intensity was low 14 days after transplantation, and there was no difference between the genotypes. Bars represent 50 μm. (E) Quantification of the fluorescent signal from the cleaved gelatin in the graft area at 3-5 days and 14 days after transplantation. *P < .05. n = 4 in each group. (F) Gr-1 staining of the engrafted islets at 3-5 days after transplantation revealed no significant difference between the groups, indicating that the difference in gelatinase activity is not the result of altered leukocyte recruitment. n.s. indicates not significant.