New pro-inflammatory cytokine IL-40 is produced by activated neutrophils and plays a role in the early stages of seropositive rheumatoid arthritis

Objective Interleukin (IL)-40 is a new cytokine related to immune system function and malignancies. Recently, an association of IL-40 with rheumatoid arthritis (RA) and externalisation of neutrophil extracellular traps (NETosis) was found. As neutrophils are implicated in RA development, we investigated IL-40 in early stages of RA (ERA).Methods IL-40 was determined in serum of treatment naïve patients with ERA at baseline (n=60) and 3 months after initiation of conventional therapy and in healthy controls (HC; n=60). Levels of IL-40, cytokines and NETosis markers were measured by ELISA. NETosis was visualised by immunofluorescence. In vitro experiments were performed on peripheral blood neutrophils from ERA patients (n=14). Cell-free DNA was analysed in serum and supernatants.Results Serum IL-40 was elevated in ERA compared with HC (p