PRODUCTION OF INTEULEUKIN-6 BY HUMAN MAST-CELLS AND BASOPHILIC CELLS

Since mast cells and basophils are thought to play a central role in s everal types of cutaneous inflammatory and allergic reactions, and sin ce interleukin-6 (IL-6) is an important mediator in these processes, w e have studied the ability of the human mast cell line HMC-1, the huma n basophilic cell line KU812, and human skin mast cells to produce IL- 6. All three cell types proved to be potent sources of this cytokine a fter appropriate stimulation. Transcription of IL-6 mRNA was first: de tectable 2 h after stimulation with the ester phorbol myristate acetat e (PMA) and the calcium ionophore A23187 in both cell lines, as eviden ced by semiquantitative reverse transcriptase polymerase chain reactio n analysis. Whereas resting cells did not produce IL-6 protein, PMA/A2 3187-stimulated cells released immunoreactive and biologically active IL-6, as demonstrated and quantitated by enzyme-linked immunosorbent a ssay and by the use of TEPC 1033 cells, an IL-6-dependent murine plasm acytoma cell line. Stimulated KU812 cells secreted sevenfold more IL-6 (up to 15 ng/ml) than HMC-1 cells (up to 2.4 ng/ml). Immunoblotting o f HMC-1- and KU812 cell-derived IL-6 revealed several IL-6 forms in th e molecular weight range of 21 to 30 kDa. Immunoelectron microscopic s tudies of human skin biopsies provided evidence that unstimulated mast cells do not contain preformed IL-6 but accumulate IL-6 in cytoplasmi c and extruded granules after IgE-dependent stimulation. These finding s suggest that IL-6 secreted by human mast cells and basophils potenti ally contributes to allergic, other immunologically mediated and nonsp ecific inflammatory responses.