Cell surface expression of MPO on unstimulated PMNs incubated with supernatants containing MPO (FACScan analysis).

(A) Expression of MPO after incubation with supernatant containing 600 U/mL MPO (bold curve), as compared with PMNs incubated with buffer (thin curve). (B) Dose-dependent decrease of MPO expression after immunodepletion of MPO in the supernatant from 570 U/mL (bold curve) to 135 U/mL (broken curve) and from 135 U/mL to an MPO concentration below detection limit (thin unbroken curve). (C) Expression of MPO after incubation of PMNs with purified MPO added to buffer at 450 U/mL (bold curve), as compared with PMNs incubated with buffer only (thin curve). (D) Expression of MPO after incubation of PMNs with supernatant containing 600 U/mL MPO in the presence or absence of 50% serum. The bold curve represents the expression level after incubation with supernatant diluted 1:1 with buffer; the thin curve, the expression level after incubation with supernatant diluted 1:1 with serum. The broken curve represents the expression after incubation with buffer. Similar results were obtained for 3 individual experiments.