Background Reduced phagocytic clearance of apoptotic cells in Juvenile-onset Systemic Lupus Erythematosus (JSLE) may lead to prolonged exposure of nuclear autoantigen to the immune system. The generation of autoantibodies against nuclear antigens can cause damage in various organs and a diversity of symptoms.
Impaired phagocytosis is also thought to increase the formation of neutrophil extracellular traps (NETs) in a process called NETosis, which may be a potential source of nuclear autoantigens in SLE.
Understanding the phagocytic potential of JSLE neutrophils is therefore important. However only very limited data is published on this subject for neutrophils, especially in juvenile-onset disease.
Transcriptomic analysis of JSLE and control neutrophils by our group found genes for phagocytosis to be differentially expressed between the two groups. These genes included receptors for pathogen recognition (TLR-2), apoptotic material (AnxA3), for microbial size (Dectin-1), for opsonized material (CR3, FcγRIIIb), and adherence to and digesting of the target (CamK1D) as well as genes thought to promote phagocytosis (S100A9).
By investigating the expression of these genes as well as the phagocytic function of JSLE neutrophils, this study aims to provide important insight into the phagocytic potential of JSLE neutrophils.
Objectives To compare the mRNA expression of phagocytosis genes in neutrophils from JSLE and paediatric healthy control patients and the ability of JSLE and control neutrophils to phagocytose different pathogens in the presence of JSLE and control serum.
Methods Neutrophil RNA was extracted from children (diagnosed <17 years) with JSLE (n=9) and paediatric healthy controls (n=8). The mRNA expression of TLR-2, Dectin-1, AnxA3, CamK1D, FcγRIIIb, CR3 and S100A9 were measured using qPCR. The expression of b-actin was analysed as an internal standard. For functional assays the neutrophils were incubated in JSLE or control serum with E.coli, S.aureus and zymosan fluorescent particles and analysed using flow cytometry and confocal microscopy.
Results Expression (fold change relative to housekeeping gene ± SEM) of TLR-2 (Control 0.013±0.001, JSLE=0.029±0.003, p=0.001) and S100A9 (Control 1.59±0.22, JSLE=2.73±0.33, p=0.02) were both significantly higher in JSLE patients compared to paediatric healthy controls. No difference was observed in CamK1D expression (p=0.94). Increased expression was also observed in the JSLE group of Dectin-1 (p=0.28), AnxA3 (p=0.18), FcγRIIIb (p=0.11) and CR3 (p=0.23), although was not statistically significant.
Early preliminary data of the functional assay indicate a general reduction of phagocytosis in JSLE compared to control neutrophils and decreased phagocytosis of each pathogen in the presence of JSLE serum.
Conclusions Here, we show increased expression of key genes involved in phagocytosis in JSLE neutrophils compared to controls. This may be reflective of the response of the cells to the apoptotic burden observed in these patients. Further assays are currently being carried out to confirm the preliminary observations noted in this study.
Ballantine et al., 2015 Pediatr Rheumatol Online J.
Chauhan et al., 2015 Immunology letters
Disclosure of Interest None declared
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