Immunohistochemistry for CCL-9 in the proximal tibia of tl rats. Immunohistochemistry after 2 (A), 4 (B), or 6 (C) days of CSF-1 injections is shown. Orange-brown color indicates CCL-9 protein. At day 2, the staining was most evident in small, newly formed osteoclasts, while at days 4 and 6, large, mature osteoclasts were present with much weaker, more diffuse labeling. *Bone trabeculae; v indicates a prominent vacuole in the large osteoclast in panel B. Scale bar in panel C equals 21 μm. Shown are 10-μm paraffin sections without counterstain. Objective magnification: 63 ×/1.25 NA.