Contrast in cytokine expression between patients with monoclonal gammopathy of undetermined significance or multiple myeloma

We investigated whether differences in IL-6 and IL-1β expression could be detected in monoclonal plasma cells from patients with MGUS or MM. Expression of IL-6 and IL-1β in bone marrow cells was determined using cell sorting to enrich for plasma cells followed by reverse transcriptase/polymerase chain reaction (RT/PCR). Nineteen patients (six MGUS, two primary amyloid (AL), 11 MM) were studied. IL-6 mRNA expression was detectable in the sorted CD38⁺/CD45^- plasma cell populations from 0/6 MGUS, 0/2 AL and 5/11 MM patients. All five MM patients with autocrine IL-6 expression demonstrated an elevated plasma cell labeling index. IL-1β mRNA was detectable in the sorted CD38⁺/CD45^- plasma cell populations from 1/6 MGUS, 0/2 AL and 10/11 MM patients. In situ hybridization (ISH) confirmed that the IL-1β producing cells were plasma cells. In conclusion, autocrine production of IL-6 parallels a high labeling index and aberrant expression of IL-1β correlates with the diagnosis of MM. Follow-up of IL-1β-positive MGUS patients will determine whether aberrant expression of IL-1β will predict those MGUS patients that will eventually progress to MM.