Résumé
Whether interleukin 6 (IL6) is an autocrine or paracrine myeloma cell growth factor
in vivo
remains unresolved. To identify which cells are producing IL 6
in vivo
, we have studied the IL 6 gene expression in bone marrow mononuclear cells (BMMC) of 19 patients with multiple myeloma (MM) and in peripheral blood mononuclear cells (PBMC) of 9 patients with plasma cell leukemia (PCL). We found that the IL 6 gene was transcribed by BMMC of most patients with MM (79%). Further, IL 6 mRNA was not produced by purified myeloma cells from patients with either MM (5 patients) or PCL, but by the bone marrow environment, mainly by monocytes and myeloid cells (CD13
+
CD15
+
cells). For 2 patients with PCL, for whom PBMC and BMMC samples were available, IL 6 mRNA could be detected in BMMC but not in PBMC. Finally, no IL 6 mRNA was detected in five freshly established IL 6‐dependent myeloma cell lines. The present data give a clear‐cut demonstration of the paracrine origin of IL 6
in vivo
in human MM.