STEAP4 and rheumatoid arthritis: Similarly, STAMP2 overexpression reduces the migration of neutrophil-like HL60 cells [64] and reduces IL-6 and IL-8 cytokine expression, whereas siRNA knockdown of STAMP2 increases cytokine signaling in patients with rheumatoid arthritis (RA) [11], again, consistent with a role for STAMP2 in a negative feedback loop.