Patients with adult respiratory distress syndrome (ARDS) demonstrate in vivo neutrophil activation associated with diminished binding of neutrophil-specific monoclonal antibody 31D8.

Neutrophils (PMNs) from patients with adult respiratory distress syndrome (ARDS) were assessed for light scattering, membrane potential, and phagocytic responses using fluorescent probes and flow cytometry to evaluate individual cells. Qualitative and quantitative oxidant responses were measured by nitroblue tetrazolium (NBT) and cytochrome c reduction assays, respectively. The results were correlated with the proportion of cells binding the PMN subset-specific monoclonal antibody 31D8. Despite an increased forward scatter signal (4.3 +/- 1.6 vs. 1.3 +/- 1.1 ARDS vs. control, P = 0.041) and spontaneous NBT test (12.6 +/- 4.7% vs. 2.5 +/- 0.8% positive, ARDS vs. control, P = 0.033) indicating in vivo priming of ARDS PMNs, there were no significant differences between ARDS and control PMNs in assays of stimulated membrane potential, NBT, and O.2- production or phagocytosis. However, positive correlations between the degree of prestimulus forward light scatter and subsequent O.2- production to FMLP (r = 0.673, P = 0.006) and between the percentage of bands and the O.2- response to PMA (r = 0.660, P = 0.003), suggest that the great variability of the ARDS PMN functional responses may relate to varying degrees of in vivo cell priming and/or deactivation. ARDS PMNs demonstrated a significantly lower percentage of 31D8 positive cells (73.4 +/- 7.5% vs. 94.5 +/- 1.6%, P = 0.012) and a lower level of 31D8 staining when compared to normals (60.1 +/- 10.4% of control level, P = 0.001). The lower 31D8 expression did not directly correlate with any functional parameter tested or with the proportion of immature cells. However, patients receiving an intravenous PGE1 infusion demonstrated a significant increase in 31D8 staining relative to controls and inhibition of PMA-stimulated O.2- production. The data suggest that the function of PMNs from ARDS patients varies widely and reflects great in vivo variation in cell priming. While the mechanism responsible for the lowered expression of the 31D8 antigen and its apparent modulation by PGE1 is unknown, 31D8 may be an indirect marker for in vivo stress factors that regulate the preferential release of a structurally distinct PMN subset from the bone marrow.