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.
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.


CONCLUSIONS
The abnormal CXCR2 modulation and impaired cationic ion transporter expression cause SLE-PMN hyporesponsiveness to IL-8 stimulation in vitro.
Hsieh
S-C
SC
Department of Internal Medicine, National Taiwan University Hospital and National Taiwan University College of Medicine, Taiwan 100, Taiwan. chialiyu@ntu.edu.tw.
Wu
T-H
TH
Tsai
C-Y
CY
Li
K-J
KJ
Lu
M-C
MC
Wu
C-H
CH
Yu
C-L
CL
D005260:Female; D005434:Flow Cytometry; D005786:Gene Expression Regulation / Q000187:drug effects / Q000276:immunology; D006801:Humans; D016209:Interleukin-8 / Q000096:biosynthesis / Q000494:pharmacology*; D008070:Lipopolysaccharides / Q000494:pharmacology; D008180:Lupus Erythematosus, Systemic / Q000235:genetics* / Q000276:immunology*; D008297:Male; D009504:Neutrophils / Q000187:drug effects / Q000276:immunology*; D012333:RNA, Messenger / Q000235:genetics; D023062:Receptors, Interleukin-8A / Q000235:genetics; D023063:Receptors, Interleukin-8B / Q000235:genetics*; D012016:Reference Values; D020133:Reverse Transcriptase Polymerase Chain Reaction
D016209:Interleukin-8; D008070:Lipopolysaccharides; D012333:RNA, Messenger; D023062:Receptors, Interleukin-8A; D023063:Receptors, Interleukin-8B