Cytokine expression in multiple myeloma and monoclonal gammopathy: analysis by reverse transcription/polymerase chain reaction and quantitative PCR.

Cytokine messenger RNA expression was studied using the reverse transcription/polymerase chain reaction in 23 patients with multiple myeloma (MM), 16 with monoclonal gammopathy of undetermined significance (MGUS), 12 with post menopausal osteoporosis, (OP) and 12 normal controls. Messenger RNAs for IL-1 alpha, IL-1 beta, TNF-alpha, TNF-beta, IL-6 and M-CSF were sought in view of their reported pathogenic role in myeloma. Transcripts for IL-1 beta, TNF-alpha, TNF-beta and M-CSF were found frequently in all four groups of patients. The only significant difference in cytokine expression between the groups was for IL-6 which was expressed in 17% of controls compared with 87% of patients with MM (p < 0.001), 62% of patients with MGUS (p < 0.02) and 67% of patients with osteoporosis (p < 0.02). Further analysis of IL-6 expression by quantitative PCR showed significantly higher IL-6 mRNA levels in MM compared with MGUS (p < 0.006). There was no correlation however between expression of individual cytokines and clinical features of myeloma such as osteolytic bone disease or hypercalcaemia. We conclude that expression of IL-6 mRNA is significantly enhanced in multiple myeloma when compared with MGUS. However, since MGUS and osteoporosis were also associated with a high prevalence of IL-6 expression when compared with controls it is probable that factors other than IL-6 are responsible for the local osteolytic lesions which characterise MM, but which are not seen in MGUS or osteoporosis.