Fig. 1

(a) Chronic inflammatory nidus in a nickel-sensitive synovium after total knee arthroplasty (H&E × 40). Immunohistochemical staining for CD4⁺ T-cell (b) and CD8⁺ T cell (c) markers shows a relative predominance of CD4⁺ infiltrate, consistent with a delayed-type hypersensitivity (CD4⁺ immunohistochemistry X 40). (d) Synovial sample from a patient in the control group (H&E × 40). Immunohistochemical staining for CD4⁺ T cell (e) and CD8⁺ T cell (f) markers shows similar levels of inflammatory infiltrate (CD8⁺ immunohistochemistry × 40). Black arrowhead denotes CD4+ staining cells