Representative diagram of intermediate affinity IL-15 receptor binding, trafficking and synthesis interactions.

<p>Quiescent NK cells constitutively express the β and γ subunits of IL-15R. <b>A</b>. Binding: IL-15 binds to receptors on the cell surface with rate <i>k_f</i> and dissociate from IL-15R with rate <i>k_r</i>. Inside the endosome, the on and off rates <i>k_fe</i> and <i>k_re</i> reflect modified binding affinity at lower pH. <b>B</b>. Trafficking: Free IL-15 receptors are constitutively internalized with rate k_endo, and the ligand bound receptor complexes are internalized with rate <i>k_int</i>. The IL-15 ligand recycles from the endosome back to the surface with rate <i>k_rec</i>, and the receptors and complexes are sorted for degradation with rate <i>k_deg</i>. <b>C</b>. Synthesis: The IL-15R synthesis is constitutive with rate <i>V_s</i> and can be induced (<i>k_syn</i>) by signaling initiated by the surface complexes.