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Neutrophils regulate their own apoptosis via preservation of CXC receptors
A Dunican1, P Grutkoski, S Leuenroth
1Division of Surgical Research, Department of Surgery, Brown University School of Medicine, Rhode Island Hospital Department of Surgery, Providence, RI 02903, USA.
Background:
Dysregulated neutrophil (PMN) apoptosis is thought to contribute to an exaggerated inflammatory response in diseases such as acute respiratory distress syndrome (ARDS) and multiple organ dysfunction syndrome (MODS). The CXC chemokines, interleukin-8 (IL-8) and growth-related oncogene alpha (Gro-alpha), contribute to the inflammatory response and suppress PMN apoptosis. We hypothesized that PMN generation of CXC chemokines is an autocrine/paracrine mechanism for amplification of the PMN inflammatory response via suppression of apoptosis.
Methods:
Freshly isolated human PMNs from healthy donors were incubated with IL-8 or Gro-alpha (100 ng/ml) for 0-12 h, and apoptosis was analyzed at 24 h. De novo synthesis of IL-8 or Gro-alpha was measured using an ELISA. To determine if receptors were available to bind these newly synthesized ligands (125)I radiolabeled monoclonal antibodies specific for each receptor (CXCRI, CXCRII) were used to determine PMN receptor density. Comparison was by one-way ANOVA.
Results:
Significant suppression of apoptosis was seen at 24 h with only 4 h exposure to IL-8 or Gro-alpha (n = 5, P < 0.05). PMNs cultured with IL-8 for 4 h produced 31 +/- 4.3 ng/ml IL-8 by 24 h; PMNs cultured with Gro-alpha produced 19.7 +/- 4.0 ng/ml Gro-alpha (n = 6, P < 0. 05). Neither chemokine induced significant production of the other chemokine. The addition of either ligand promoted upregulation of CXCR1 (n = 4, P < 0.05) at 24 h. However, CXCR2 was downregulated by Gro-alpha and IL-8 to 71 +/- 7.5 and 79 +/- 6.3% of control, respectively (P < 0.05).
Conclusion:
IL-8 and Gro-alpha, which suppress apoptosis, stimulate their own production after short-term incubation with PMNs. PMNs maintain the ability to respond to these chemokines through expression of the CXC receptors which suggests that PMNs are active participants in the suppression of apoptosis at inflammatory sites. CXCRI remains upregulated after prolonged stimulation and may be an important target for mediating neutrophil responses to IL-8.