IL-34 expression in MOPC315.BM cells. (A) PCR analysis of Il34, Cd138, and Gapdh expression in MOPC315.BM cells compared with normal plasma cells. (B) Relative expression of Il34 expression in MOPC315.BM cells compared with normal plasma cells (normalized to Gapdh). (C) Enzyme-linked immunosorbent assay (ELISA) measurement of IL-34 in the supernatants of MOPC315.BM cells stimulated for 7 days with IL-1β, IL-6, TGFβ, or TNFα (100 ng/mL) compared with PBS. (D) qRT-PCR analysis of Il34 expression in MOPC315.BM cells purified directly from the BM (day 30 after IV injection) or cultured in vitro compared with plasma cells (normalized to Gapdh). (E) Individual variability of MOPC315.BM cells homing to the bones. Top panel, The bioluminescence signals in representative BALB/c mice challenged with Luc⁺GFP⁺ MOPC315.BM cells compared with healthy controls. Bottom panel, Populations of CD138⁺GFP⁺ cells (MOPC315.BM) in the BM of femurs as analyzed by flow cytometry (day 30 after IV injection). (F) The correlation between frequencies of Luc⁺GFP⁺ MOPC315.BM cells with bioluminescence signals in femurs. (G) The correlation between frequencies of Luc⁺GFP⁺ MOPC315.BM cells with protein levels of IL-34 in the BMF of femurs. Red dots indicate levels of normal IL-34 levels in healthy controls. Data are mean ± standard error of the mean (SEM); *P < .05. ddCt, delta-delta cycle threshold; P/S, photon/second.