Cytokine detection by flow cytometry/RT-PCR. Marrow aspirates were sorted by flow cytometry using anti-CD38 and anti-CD45 antibodies. Messenger RNA was isolated from 10⁵ to 10⁶ unsorted (U) and sorted CD38⁺/CD45⁻ (S) cells. Subsequently, RT-PCR with specific cytokine primers was performed to detect the presence of message for IL-1β and actin. IL-1β mRNA was detectable in sorted CD38⁺/CD45⁻cells from the myeloma patient but not from the MGUS patient.