Abnormal in vitro CXCR2 modulation and defective cationic ion transporter expression on polymorphonuclear neutrophils responsible for hyporesponsiveness to IL-8 stimulation in patients with active systemic lupus erythematosus
1Department of Internal Medicine, National Taiwan University Hospital and National Taiwan University College of Medicine, 2Institute of Clinical Medicine, National Yang-Ming University College of Medicine, 3Section of Allergy, Immunology and Rheumatology, Taipei Veterans General Hospital, 4Division of Immunology, Rheumatology and Allergy, Buddhish XinDian Tzu-Chi General Hospital and 5Division of Immunology, Rheumatology and Allergy, Buddhish Dalin Tzu-Chi General Hospital, Chia-Yi, Taiwan.
Correspondence to: C.-L. Yu, Department of Internal Medicine, National Taiwan University Hospital, # 7 Chung-Shan South Road, Taiwan 100, Taiwan. E-mail: chialiyu{at}ntu.edu.tw
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Abstract |
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Objective. To elucidate the molecular basis of hyporesponsiveness of polymorphonuclear neutrophils (PMN) to interleukin-8 (IL-8) stimulation in patients with active SLE.
Methods. PMN obtained from active SLE and well-matched healthy individuals were studied. The expression of two IL-8 receptors, CXCR1 and CXCR2, in PMN were detected by flow cytometry and reverse transcriptase-polymerase chain reaction. The binding affinity of PMN with IL-8 was calculated by Scatchard plotting. Soluble CXCR2 level in IL-8-stimulated PMN culture supernatant was measured by sandwich enzyme-linked immunosorbent assay. The resting and IL-8-stimulated membrane potential (MP) changes, and membrane expression of cationic ion transporters including Na+-K+-ATPase, renal epithelial Na+ channel (ENaC) and renal outer medullary epithelial K+ channel 1 (ROMK1) on PMN were detected by flow cytometry.
Results. Compared with normal PMN, decreased CXCR2 gene expression, but normal IL-8-binding affinity of SLE-PMN, was found. For exploring the molecular basis of the defect, the modulation of CXCR2 in SLE-PMN was intensively investigated. We found that increased cytosolic CXCR2 expression in SLE-PMN was due to defective surface translocation, increased spontaneous internalization and/or increased spontaneous synthesis. The IL-8-induced CXCR2 down-regulation in SLE-PMN was also impaired due to decreased proteolytic cleavage of IL-8–IL-8 receptor complexes from the cell surface whereas IL-8-induced internalization of the complexes was normal. In addition, we originally found that increased resting but decreased IL-8-stimulated MP in SLE-PMN was relevant to defective expression of Na+-K+-ATPase, ENaC and ROMK1 on the cell surface.
Conclusion. The abnormal CXCR2 modulation and impaired cationic ion transporter expression cause SLE-PMN hyporesponsiveness to IL-8 stimulation in vitro.
KEY WORDS: Systemic lupus erythematosus, Polymorphonuclear neutrophil, Hyporesponsiveness, CXCR2 modulation, Membrane potential, Cationic ion transporters
Submitted 5 April 2007;
revised version accepted 1 November 2007.
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