Effect of the metalloproteinase inhibitors 1,10-phenanthroline and EDTA on LPS-, TNF-–, and IL-8–induced downmodulation of CXCR1 and CXCR2. Purified peripheral blood PMNs were preincubated with (A,B) 1,10-phenanthroline (Phen, 0.5 mmol/L) or (C,D) EDTA (5 mmol/L) for 30 minutes in media (RPMI/10% fetal calf serum) followed by the addition of LPS (100 ng/mL), TNF- (50 ng/mL), or IL-8 (500 ng/mL) for 1 hour at 37°C. CXCR1 and CXCR2 expression was measured cytofluorometrically. The x-axis indicates fluorescence intensity measured on log₁₀ scale, and the y-axis indicates event counts per channel on a linear scale. MFI values for individual histograms are indicated above each histogram.