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ACTIVATED NEUTROPHILS INHIBIT PHAGOCYTOSIS BY HUMAN MONOCYTE CELLS IN VITRO
Citation:
WU, W., N. ALEXIS, F. DIMEO, P. A. BROMBERG, AND D. PEDEN. ACTIVATED NEUTROPHILS INHIBIT PHAGOCYTOSIS BY HUMAN MONOCYTE CELLS IN VITRO. Presented at American Thoracic Society Meeting, San Diego, CA, May 19 - 24, 2006.
Description:
We have previously reported the correlation of decreased phagocytosis of opsonized zymosan by sputum monocytic cells with the increase in sputum neutrophils in volunteers 6h after inhalation of endotoxin (20,000 EU) (Alexis, et al. JACI, 2003;112:353). To define whether an intrinsic association exists between these two events, purified neutrophils and monocytes from peripheral blood of healthy subjects were co-incubated in vitro at ratios of 1:1 and 10:1 overnight and examined for their interaction. Activation of PMNs by fMLP stimulation was evident within 2 hours, showing an increase in the production of reactive oxygen species and release of myeloperoxidase. Monocyte phagocytosis was assayed using IgG-opsonized zymosan particles and measured using flow cytometry and expressed as mean fluorescence intensity (MFI). Monocyte viability was measured using Trypan Blue exclusion staining and did not fall below 85% at any time. Co-incubation of monocytes with unstimulated or fMLP-activated PMNs (1:1 PMN: monocyte ratio), reduced monocyte phagocytic capability by 23% and 30% of baseline (phagocytosis of monocytes alone), respectively. At the ratio of 10:1, monocyte phagocytosis was reduced by 28% and 46% of baseline for unstimulated and fMLP-activated PMNs, respectively. This phenomenon was also observed when PMNs were co-incubated with a human monocytic cell line (THP-1). Conditioned media from fMLP-activated PMNs produced a slight inhibitory effect on monocyte phagocytosis (10% reduction from baseline), suggesting that PMN-monocyte contact may be important to this phenomenon. The ability of neutrophils to adversely affect the phagocytic capability of monocytic cells has important host defense implications for airway diseases that are marked by neutrophilic inflammation (asthma, COPD, CF). This work does not necessarily reflect EPA policy. (This work was supported by US EPA Cooperative Agreement CR#829522 awarded to the CEMALB, UNC).