IL15 and rheumatoid arthritis: While proinflammatory factors such as GM-CSF, IFN-γ, IL-9, and IL-15 can reduce the induction of apoptosis and extend the lifespan of the neutrophils from RA patients in vitro, both IL-8 and IL-18 show no effect on this phenotype [27, 28, 32, 57–59].