Immune complexes induce TNF-α and BAFF production from U937 cells by HMGB1 and RAGE

OBJECTIVE: This study investigated the effects of immune complexes (ICs) on tumor necrosis factor α (TNF-α) and B cell-activating factor (BAFF) production from U937 cells and further explored the mechanism.

MATERIALS AND METHODS: U937 cells were incubated with necrosis supernatant or systemic lupus erythematosus (SLE) sera alone, or their combination. The expression of TNF-α and BAFF was determined by Real-time polymerase chain reaction and enzyme-linked immunosorbent assay. High mobility group box protein 1(HMGB1) A-box was produced by gene recombination. HMGB1 A-box and anti-receptor for advanced glycation end products (RAGE) antibody were adopted in the blocking experiments. The importance of DNA for cytokine induction was investigated by DNase treatment.

RESULTS: The combination of necrosis supernatant and SLE sera induced the expression of TNF-α and BAFF significantly increased compared to necrosis supernatant or SLE sera alone. Recombinant HMGB1 A-box protein was purified, and TNF-α and BAFF production, which were induced by this combination, was blocked via HMGB1 A-box and anti-RAGE antibody. Moreover, we found that DNA component is important for the immunostimulatory activity of this combination.

CONCLUSIONS: ICs containing DNA can promote TNF-α and BAFF production in U937 cells, and this process can be mediated by HMGB1 and RAGE. One possible mechanism of increasing BAFF production in SLE is proposed in this study whereby B cell activation, antibody production and ICs stimulated monocytes may create a vicious cycle that leads to B cell hyperactivity, which can be of importance for SLE etiopathogenesis.

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