Role of complement activation in cellular activation by systemic lupus erythematosus (SLE) immune complexes (ICs)

Abstract

Abstract Complement (C’) activation is a prominent feature of SLE ICs, but the mechanism by which C’ mediates cellular activation by ICs is not well understood. To investigate this question, we formed SLE ICs in situ in healthy donor (HD) whole blood (WB) by adding SLE plasma (n=1–3;10% v/v) or HD plasma (as a control) along with apoptotic bodies (generated from RAW 264.7 cells) or RNP-Sm antigen (Arotec Diagnostics, New Zealand) with and without C’ inhibitors (CI). For cellular binding studies, WB was incubated for 45 minutes at 37°C and deposition of C3c and human IgG (ICs) on blood cells was examined by flow cytometry. In these studies, we noted that C’ inhibition significantly reduced deposition of C3c and ICs on B cells {% reduction: C3c (97%) and IgG (97%)}, monocytes {% reduction: C3c (40%) and IgG (49%)} and neutrophils {% reduction: C3c (69%) and IgG (70%)}. To investigate cellular activation, WB was incubated for 22 hours and cellular activation was measured by HLA-DR expression on monocytes by flow cytometry and cytokine release (IL-8, IL-6 and TNF) by ELISA. Incubation of WB with SLE ICs, but not ICs made with HD plasma (control ICs), resulted in increased HLA-DR expression on monocytes (MFI control ICs: 1609 V SLE ICs: 11096), which was susceptible to C’ inhibition (MFI SLE ICs with CI: 4975). Similarly, inflammatory cytokine release by SLE ICs was also significantly inhibited with C’ inhibition {% inhibition: IL-8 (75 %), IL-6 (99%) and TNF (99 %)}. Taken together, our results show significant C’-dependent effects of SLE ICs on cellular binding and activation. Additional studies are underway to investigate the prevalence of C’ activating ICs in SLE patient and correlate their presence with clinical disease. Wendell F. Rosse Complement Research Award, Duke University Medical Center (SK) and Duke Scholars Award, Duke University Medical Center (GMA)