IL-3 expression and secretion in MM patients. (A) Interleukin-3 (IL-3) and IL-3 receptor mRNA expression was evaluated by RT-PCR in human myeloma cell lines (RPMI-8226, XG-1, XG-6, U266, OPM2, JJN3, ARP-1, and H929) and in freshly purified MM cells as shown for 12 representative MM patients (CON+ = activated T cells). (B) IL-3 mRNA expression was checked in bone marrow mononuclear cells (BMMCs), BM stromal cells (BMSCs), and in purified BM CD14⁺, CD20⁺, and CD3⁺ (CD4⁺ and CD8⁺) cells obtained from MM patients and MGUS subjects as shown for 4 representative patients. (C) IL-3 levels were measured by ELISA in 48-hour supernatants of purified CD3⁺ cells obtained from MM patients (n = 20) and MGUS subjects (n = 10). Graph represents the mean ± SD IL-3 levels normalized to 10⁶ cells (^*P = .01).