Increased number of osteoclasts generated from long bone, calvaria, and jaw but not vertebra marrow cells of Il1rn−/− mice. Bone marrow cells from long bone, calvaria, vertebra, and jaw were cultured with 30 ng/mL M-CSF and 20 ng/mL RANKL on bone slices for 6 days. Osteoclasts were stained for tartrate resistant acid phosphatase (TRAcP), counted, and categorized as 3–5 nuclei, 6–10 nuclei, 11–20 nuclei, and >20 nuclei. The number of osteoclasts (≥3 nuclei) was counted for long bone (A), calvaria (B), vertebra (C), and jaw (D) and compared between wild-type (WT) and Il1rn−/− mice. The total number of osteoclasts is shown as multinucleated cells (MNCs). Osteoclastogenesis was significantly higher in long bone, calvaria, and jaw of Il1rn−/− osteoclast precursors (OCPs) compared to WT OCPs. In contrast, WT and Il1rn−/− OCPs isolated from vertebrae formed a comparable number of osteoclasts (n = 6 mice/group, *p < 0.05, **p < 0.01, ***p < 0.001).