TRAP staining
TRAP staining of CD14+ monocytes and RAW264.7 macrophages was performed after culturing with or without CXCL2 in the presence of M-CSF and RANKL. TRAP staining was conducted using the TRAP kit (387A-1KT, Sigma) in accordance with the manufacturer’s instructions. TRAP-positive multinucleated cells containing more than 3 nuclei were identified as osteoclasts and counted under a microscope.