Impaired clearance of apoptotic cellular debris by macrophages was recently suggested as a mechanism leading to the systemic pathogenesis of systemic lupus erythematosus patients. Serum Amyloid P component (SAP) is a plasma protein that binds apoptotic cells and macrophages.
To investigate the ability of SAP protein and its synthetic peptide derivates to enhance the clearance of apoptotic cells by macrophages in vitro.
Macrophages were isolated from peripheral blood cells of 30 healthy donors and the purity was confirmed by FACS analysis using CD14-PE. Apoptosis was induced in Jurkat cells using anti-Fas antibodies and confirmed by staining with a caspACE™ FITC-VAD-FMK. The apoptotic cells were introduced to macrophages in the presence/absence of SAP protein and SAP synthetic peptide derivatives. Clearance of labeled apoptotic cells by macrophages, in vitro, was detected by FACS and analyzed under fluorescence microscope.
In the presence of SAP, the clearance of apoptotic cells increased twice (index 2.03) compared with the control (index 1). In the presence of SAP derivate synthetic peptide (marked as peptide 26), an increase of 53% (index 1.53) was detected. A D-form of the SAP synthetic derivate peptide was used as a negative control and gave a clearance index of only 1.1 in comparison with the control. A significant correlation was found between the concentration of SAP protein and SAP synthetic peptide derivates and the clearance index.
Herein we show the role of SAP and SAP-derived synthetic peptides in accelerating clearance of apoptotic cells by macrophages in vitro. Our results may pave the way for future development of SAP-derived synthetic peptides for apoptotic cell clearance improvement in systemic lupus erythematosus patients.