NK cells express more CXCR1 than CXCR2. CXCR1 and CXCR2 expression was determined on untreated freshly isolated human PBMCs from 3 separate blood donors by immunofluorescence with gating on CD56⁺ CD3⁻ cells. Histograms show isotype control (filled gray) or CXCR1 or CXCR2 staining (thick black line), as indicated.