Neural activities of IL-6-type cytokines often depend on soluble cytokine receptors

Cytokines of the interleukin-6 (IL-6) family participate in regulatory and inflammatory processes within the nervous system. IL-6, ciliary neurotrophi c factor (CNTF) and IL-11 act via specific membrane receptors which, togeth er with their ligands, associate with signal-transducing receptor subunits thereby initiating cytoplasmic signalling. Cells which only express signal- transducing receptor subunits but no ligand binding subunits for IL-6, CNTF and IL-11 are refractory to these cytokines. An unusual feature of the IL- 6 cytokine family is that the soluble forms of the ligand binding receptor subunits generated by one cell type in complex with their ligands can direc tly stimulate the signal-transducing receptor subunits on different cell ty pes which lack ligand binding receptor subunits. This process has been name d transsignalling. This article focuses on the importance of transsignallin g events in neuronal differentiation and survival responses.