Effects of an anti–IL-3 neutralizing antibody on OCL formation stimulated by bone marrow plasma from patients with MM. Bone marrow plasma from MM patients containing varying amounts of IL-3 and MIP-1α were dialyzed against α-MEM for 48 hours. Human bone marrow culture was treated with dialyzed bone marrow plasma from patients with MM at the 30% (vol/vol) concentration for 3 weeks in the presence and absence of anti–IL-3 neutralizing antibody (500 ng/mL). Cultures not treated with bone marrow plasma or cultures treated with isotype IgG were used as controls for these experiments. Results represent the mean ± SEM for quadruplicate determinations for a typical experiment (^*P < .05). Similar results were seen in 2 independent experiments.