Fig. 4

The in situ distribution of CD105⁺ and CD271⁺ cell in paired grade 1–2 and grade 3–4 OA cartilages. a, b The general morphological characteristics of paired human knee osteoarthritic cartilages were showed by HE staining (n = 12 donors). c–f The results of CD105-targeted immunohistochemical staining showed that more CD105⁺ cells remained present in the grade 3–4 OA cartilage and the bone lining locations near the osteochondral junction area as showed by the arrow (n = 8 donors). For CD271⁺ cell distribution, only a few CD271⁺ cells were observed in the superficial cartilage surface of grade 1–2 OA cartilage (g). However, more CD271⁺ cells were found in the superficial cartilage surface of grade 3–4 OA cartilage as showed by the arrow (i). In addition, CD271⁺ cells distributed near the osteochondral junction regions and reticular pattern of subchondral bone marrow cavities in both grade 1–2 and grade 3–4 OA subchondral bones (h and j). Scale bars represent 500 μm (a, b) and 100 μm (c–h), respectively