IL-15 participates in innate immune cross-talk between activated monocytes/macrophages and NK cells.

After an infectious insult (1), macrophages produce monocyte-derived cytokines (monokines) (2), including IL-15, that bind to constitutively expressed monokine receptors on NK cells. Monokine-stimulated NK cells in turn produce cytokines that activate the macrophage (3), including IFN-γ, allowing the macrophage to clear the offending pathogen and stimulating further monokine production.