Induction of IL-6 production by bone marrow stromal cells on the adhesion of IL-6-dependent hematopoietic cells.

Cellular interactions between hematopoietic cells and stromal cells play crucial roles in the proliferation and differentiation of the hematopoietic cells. Interleukin-6 (IL-6)-dependent 7TD1 cells markedly proliferated without IL-6 when they were co-cultured with hematopoietic-supportive bone marrow stromal cells, HESS-5 cells and HESS-1 CL.3 cells, which can support long-term hematopoiesis in vitro with but not without direct cell contact, cell contact being prevented with a microporous membrane. The production of IL-6 and the amount of IL-6 mRNA in hematopoietic-supportive stromal cells but not 7TD1 cells significantly increased only when the stromal cells were co-cultured in direct contact with 7TD1 cells. Furthermore, the amount of IL-6 mRNA increased according to the number of 7TD1 cells co-cultured. These inductions were not observed on co-culture with a murine myeloid cell line, M1 cells, or on the addition of the co-culture supernatant. These results suggest that 7TD1 cells transmit the signal to stromal cells that enhances IL-6 production by stromal cells via direct cell contact. A certain specific molecule for transduction of the signals may exist on the surface membrane of stromal cells and hematopoietic cells.