Eosinophil-associated matrix remodeling in a sterile granulomatous inflammation model: a temporal histopathological analysis

Eosinophils are increasingly recognized as contributors to tissue remodeling and chronic inflammation, yet their spatiotemporal behavior in sterile granulomatous reactions is incompletely defined. We performed a day 1-14 histopathological time course of a reproducible sterile granuloma induced by implantation of a heat-coagulated egg white pellet into the murine peritoneum. The reaction showed a biphasic inflammatory pattern with early neutrophil predominance followed by a sustained eosinophil-rich phase that persisted through late remodeling. Across time points, lesions progressed from exudative inflammation with prominent fibrin to organized fibroplasia and neovascularization, culminating in collagen-dominated encapsulation by day 14. Eosinophils concentrated at the pellet-tissue interface, frequently displaying apoptosis and degranulation, and occurring in close spatial association with fibroblasts and macrophages. At late time points, the outer granuloma zone contained mononuclear phagocyte/macrophage-like cells alongside dense connective tissue maturation. Together, these findings provide a temporal histopathology atlas of sterile implant granuloma maturation and introduce a semiquantitative framework that summarizes key tissue-composition transitions (fibrinous exudate → fibroplasia/collagen encapsulation) alongside eosinophil enrichment at the pellet-tissue interface.