Embolization with microspheres is widely applied to treat uterine fibroids However the foreign body reaction that could result from the degradation of the microspheres remains to be evaluated to adequately appreciate the tissular tolerance to such biomaterials We compared herein the in situ degradation of PMMA microspheres coated with polyphosphazene (PMMA-PPms) and trisacryl gelatin microspheres (TGms) and we thoroughly investigated the induced local inflammatory responses at 1 and 4 weeks after uterine artery embolization in sheep by using immunohistochemistry and microarray analyses PMMA-PPms underwent an acute and partial degradation that was associated with the early recruitment of phagocytic cells (CD172a+ and MHCII+) and with the up-regulated expression of genes involved in the movement of phagocytes (ALOX5AP CXCL2 CXCL5 IL8 PTGS2 YARS) By contrast TGms were not degraded and triggered a different inflammation profile including the recruitment of FBR Giant Cells and T-lymphocytes (CD4+) and the increased expression of genes involved in lymphocyte activation (CXCL10 IL2RG IRAK4 MALT1) Our results indicate that in contrast to a non-degradable microsphere such as TGms which is associated to a poorly inflammatory foreign body reaction that rapidly resolves PMMA-PPms which is partially degradable rapidly recruits and activates inflammatory phagocytes thus delaying the resolution of the foreign body reaction (C) 2010 Elsevier Ltd All rights reserved