Effects of IL-3 in combination with MIP-1α or RANKL on OCL formation. Human bone marrow mononuclear cells were cultured with IL-3 in combination with MIP-1α and RANKL. (A) Treatment of human bone marrow cells with 100 pg/mL IL-3 in combination with 200 pg/mL hMIP-1α or 10 ng/mL RANKL for the entire culture period significantly increased OCL formation (23c6⁺ multinucleated cells [MNCs]) compared with control cultures that were treated with only IL-3, MIP-1α, or RANKL. (B) Treatment of human bone marrow cells with 100 pg/mL IL-3 for the first week of culture period in combination with 200 pg/mL hMIP-1α or 10 ng/mL RANKL at the second and third weeks of the culture period further increased OCL formation compared with control cultures that were treated with media for the first week of the culture period. (C) The numbers of large OCLs (more than 10 nuclei per OCL) were quantified in these cultures. IL-3 markedly increased the number of large OCLs. (D) Pit formation on dentine slices by OCLs formed in cultures treated with 100 pg/mL IL-3 for the first week and followed by 200 pg/mL MIP-1α or 10 ng/mL RANKL was increased compared with that of control cultures treated with MIP-1α or RANKL alone. Results represent the mean ± SEM for quadruplicate determinations for a typical experiment. Similar results were seen in 4 independent experiments (^*P < .05).