Addition of IL-15 did not affect the percentages of CD56+CD3− NK cells in both RA patients and healthy volunteers (RA 15.5 ± 1.5% vs. 14.8 ± 1.5%, p = 0.399; healthy volunteers 8.3 ± 0.9% vs. 7.7 ± 0.8%, p = 0.14). Here, IL15 is linked to rheumatoid arthritis.