Monoclonal anti‐double stranded DNA antibody is a leucocyte‐binding protein to up‐regulate interleukin‐8 gene expression and elicit apoptosis of normal human polymorphonuclear neutrophils

OBJECTIVES: To determine whether anti-double stranded DNA (anti-dsDNA) autoantibody could bind and affect the functions of normal human polymorphonuclear neutrophils (PMN). METHODS: Normal human PMN were incubated with different concentrations of a monoclonal mouse anti-dsDNA antibody (12B3) or mouse isotype-matched IgG2a. The binding of anti-dsDNA and PMN was measured by flow cytometry and interleukin-8 (IL-8) gene expression in PMN was detected by enzyme-linked immunosorbent assay (ELISA) and reverse transcription-polymerase chain reaction (RT-PCR). PMN apoptosis was justified by morphological changes. The cognate antigen(s) of anti-dsDNA on the PMN surface was identified by membrane biotinylation, immunoprecipitation and Western blot. RESULTS: The binding of PMN with anti-dsDNA was much higher than with non-specific mouse IgG2a (70.8 vs 2.0%). Anti-dsDNA at concentrations higher than 12.5 ng/ml significantly enhanced the production and mRNA expression of IL-8 by PMN. However, anti-dsDNA facilitated PMN apoptosis after 3 h incubation. Western blot analysis of biotinylated PMN cell lysates demonstrated that a 50-52 kDa membrane molecule is the cognate antigen of anti-dsDNA. CONCLUSIONS: Anti-dsDNA autoantibody up-regulates IL-8 gene expression and elicits activation-induced cell death (AICD) of human PMN via binding to a 50-52 kDa membrane-expressed molecule.