Presence of antibodies to SSB/La is associated with decreased phagocytic efficiency of neutrophils in patients with systemic lupus erythematosus

Abstract

SSB/La antigen, expressed on surface of polymorphonuclear neutrophils (PMN), is one of the cognate antigens recognized by antineutrophil antibodies. The present study was aimed to assess PMNs in systemic lupus erythematosus (SLE) patients for their phagocytic efficiency and its correlation with history of infections and presence of anti-SSB/La antibodies and their capacity to produce interleukin (IL)-12 in response to lipopolysaccharide (LPS) with or without interferon gamma (IFN-gamma). Fifty patients with SLE, fulfilling American College of Rheumatology criteria of diagnosis, and 20 healthy controls were enrolled for the study. Phagocytic efficiency was evaluated by flow cytometry, using flourescein isothiocyanate (FITC)-labeled Escherichia coli, and expressed as mean channel fluorescence (MFI). PMNs were stimulated with LPS or LPS + IFN-gamma for 18 h, IL-12p40 was estimated in supernatants by enzyme-linked immunosorbent assay, and anti-SSB/La antibodies were detected in serum by Western blot. The mean MFI values were significantly lower in patients with SLE than controls (P < 0.0001), and among patients, it was lower in patients with history of infection than in those without (P < 0.005). Anti-SSB/La positivity was also associated with lower MFI (P < 0.005) and higher frequency among patients with history of infective episodes (P < 0.05). LPS- and LPS + IFN-gamma-stimulated IL-12 levels were lower among SLE patients than in controls. However, there was no difference in the levels of IL-12 between patients with and without history of infection. These data suggest that the autoantibodies to SSB/La may modulate PMN function in SLE.