Attempts to convert dermal fibroblasts or OA-FLS into RA-FLS using stimulation with IL-1β or a mixture of pro-inflammatory cytokines under hypoxia/normoxia were not successful [29], which suggests that the pro-inflammatory milieu is not sufficient to induce the de-differentiation of FLS in arthritic joints, and normal FLS and RA-FLS are somewhat different cell lineages. Here, IL1B is linked to rheumatoid arthritis.