Fig. 4

Immune cells distribution in OA synovial tissues and aseptic interface membranes. a Histological grading for macrophage (CD68+ cells) infiltration in tissues. b In OA, macrophages (brown cells) were almost found at LL. c Intense macrophage (brown cells) infiltration was detected in synovial membrane-like interface tissues. d In aseptic interface tissues, macrophages (brown cells) were often found surrounding or phagocytosing prosthetic debris such as polymeric particles (PP) and ZrO₂ particles (black arrows). e HLA-DR + cells—an M1 macrophage marker. f CD163+ cells—an M2 macrophage marker. g Histological grading for multinucleated giant cells in tissues h Multinucleated giant cells (GC) phagocytosing a big PP particle with ZrO₂ particles (black arrows) entrapped inside. i Histological grading for T cells (CD3+ cells). j Perivascular T cells (brown cells) clusters in OA synovial tissue. k Histological grading for B cells (CD20+ cells). l B cells (brown cells) in lymphocyte aggregates around blood vessels but in lower number than T cells. m Histological grading for polymorphonucleated cells (PMNs). n Increased number of PMNs (black arrows) in synovial membrane-like tissue with macrophages (brown cells, CD68+ cells). Masson’s trichrome staining (h) and immunohistochemistry (b, c, d, e, f, j, l, n). Scale bars correspond to 500 μm (b, c) and 50 μm (d, e, f, h, j, l, n). Semi-quantitative histological evaluation was performed in synovial tissues retrieved from 11/15 OA and 19/20 AL patients. *p < 0.05, ***p < 0.001. Chi square test was used to compare OA and AL groups