TNF and rheumatoid arthritis: The effect of the SF IC from juvenile RA patients on healthy PBMCs was studied by Jarvis et al. They found that especially the high molecular weight IC, separated by size exclusion chromatography from the other immunoglobulins and low molecular weight IC, were responsible for inducing a spectrum of pro-inflammatory cytokines, such as TNFα, IL-1β, IL6, IL8 and granulocyte-macrophage colony-stimulating factor (GM-CSF) [9].