Selective inhibition of IL-6 trans-signalling reveals distinct mechanisms of human classic and trans-signalling receptor-complex formation.

The cytokine interleukin-6 orchestrates inflammation through two distinct pathways of receptor activation: anti-inflammatory classic signalling via membrane-bound interleukin-6 receptor and pro-inflammatory trans-signalling via soluble interleukin-6 receptor. Current interleukin-6-targeted therapies block both pathways, thereby disrupting essential homeostatic functions initiated by classic signalling. We here show a high-affinity, human-specific antibody that selectively inhibits interleukin-6 trans-signalling. This antibody maintains classic signalling-induced expression of hepatic acute phase genes while completely blocking trans-signalling-induced activation of endothelial cells. By targeting the domain D2 of membrane-bound and soluble human interleukin-6 receptor, the antibody selectively prevents formation of the trans-signalling receptor complex without interfering with ligand binding. This selective blockade demonstrates that human interleukin-6 classic and trans-signalling proceed through distinct receptor assemblies. Our findings describe mechanistic insight into interleukin-6 receptor assembly and provide a strategy to suppress inflammatory interleukin-6 activity while preserving regenerative and anti-inflammatory signalling, thus offering both conceptual and potential therapeutic advances in the targeted modulation of cytokine signalling networks.