IL6 and rheumatoid arthritis: Sensory nerve fibres are known to be present in the deeper layers of the synovium in RA, now commonly referred to as sub-lining.7 8 Pro-inflammatory cytokines in the joint, such as interleukin 6 (IL-6) and tumour necrosis factor (TNF)-alpha, have their corresponding receptors on these sensory nerve fibres and are thought to initiate noxious signalling which is relayed via nociceptive pathways in the spinal cord to the brain where they can be perceived as pain.9