Hemophilic synovium expresses proangiogenic mediators and myeloid cells. Immunohistochemical analyses using DAB revealed positive staining for proangiogenic mediators VEGF-A (A), MMP-9 (B), and SDF-1 (C), in hemophilic synovium but not control synovium (D) (original magnification ×200). Immunohistochemical staining for CD68 (E) and CD11b (F) provided evidence for the presence of myeloid cell infiltration not observed in control synovium (G). Quantitative assessment of CD68⁺ cells in hemophilic and control synovium demonstrated an increased percentage of CD68⁺ cells in hemophilic synovium (HJD) compared with control (CNTRLs) (H). Immunofluorescent staining (red arrow) demonstrates CD11b⁺ cells coexpressing VEGF-R1 (I) in hemophilic synovium. Hemophilic synovium also contained VEGFR1 (red arrows) cells coexpressing the early HPC marker c-kit (J). These CD68⁺ cells expressed VEGF showing coexpression within the hemophilic synovium (K). Total number of sections stained for both experimental and control groups detailed in “HJD synovium expresses proangiogenic mediators and myeloid cells” (original magnification ×400).