Effect of serum from systemic lupus erythematosus (SLE) patients on the induction of mononuclear cell (lymphocyte and monocyte) death and apoptosis

Abstract

Background: Apoptosis is one of the crucial processes related to pathogenesis and disease severity in systemic lupus erythematosus (SLE). Previous studies have reported changes in protein levels in the sera and plasma of SLE patients. The capacity of these serum molecules to induce the apoptosis of circulating cells remains unclear. The present study investigates the effect of SLE patients’ sera on the apoptosis of mononuclear cells and explores serum and plasma proteins related to apoptotic mechanisms.

Methods: Peripheral blood mononuclear cells (PBMCs) from healthy individuals were isolated and H₂O₂ concentrations and incubation time points for optimal stimulation of cell death were determined. The PBMCs were treated with sera from SLE patients (N=12) and healthy individuals (N=12) with or without H₂O₂ induction. The level of cell death and apoptosis in both the early and late phases was examined by staining with trypan blue and annexin-V/PI, respectively. Finally, the altered serum and plasma proteins from SLE patients reported in previous publications were comprehensively collected, their associations with apoptotic mechanisms were analyzed using the STRING bioinformatics tool, and their increased serum levels in SLE patients were validated by ELISA assay.

Results: We applied 0.2 mM H₂O₂ for 48 hours as a chemical inducer of apoptosis in PBMCs. After the intervention, PBMCs exposed to SLE serum had significantly increased cell death and early- and late-phase apoptosis compared with those exposed to the sera of healthy controls both with and without H₂O₂ induction (p < 0.05). Moreover, STRING analysis revealed that 14 of the 45 collected proteins from SLE patients’ sera and plasma in several previous proteomics studies were intimately associated with the apoptotic process and regulation of apoptosis, including high mobility group box chromosomal protein 1 (HMGB1), interleukin-6 (IL-6), and clusterin (CLU). Finally, the level of serum IL-6, one of the candidate altered proteins in SLE patients, was found to be significantly increased compared with healthy controls (p < 0.05).

Conclusions: The serum of SLE patients can influence the death of mononuclear cells through the early and late phases of apoptosis. Furthermore, SLE patients’ sera was found to contain 14 altered proteins involved in the process of apoptosis, possibly as crucial factors for the progression of SLE.