Background Systemic Lupus Erythematosus(SLE) is characterised by complex interactions between both the innate and adaptive immune systems. Natural Killer(NK) cells and NK T cells(NKT) are increasingly recognised to play a significant role in the dysregulated immune response seen in SLE, with members of the Toll like receptor(TLR) family, specifically TLR7 and TLR9, identified as key players also.
Objectives To characterise the activation state of SLE NK and NKT cells in their resting state and following TLR stimulation.
Methods Following PBMC isolation from SLE patients surface activation of CD56+CD3-(NK) and CD56+CD3+(NKT) cells was characterised in the resting start and following TLR stimulation by flow cytometry using the following markers:CD69 and CD25. All samples were stimulated with TLR 3,4,7 and 9. Serum cytokine levels were determined by multiplex technology. Disease Activity was recorded by SLEDAI with a score >6 reflecting active disease. Differences in activation states were examined using the Mann Whitney test whilst Spearmans correlation coefficient was used to assess the relationship between cytokine levels, disease activity and monocyte activation.
Results 25 Patients with SLE were recruited. In the resting state SLE patients NK cells and NKT cells have higher expression of surface CD69 compared to controls(NK Cell 30.1% v 20.3%, p=.013)(NKT Cell 7.4% v 2.3 %, p =0.002). In contrast a significant difference for CD 25 expression was seen in SLE patients NK cells only(0.9% v 0.5%, p=0.0142). In addition active SLE patients have higher NKT cell CD69 surface expression than inactive patients, a finding not seen in SLE patients NK Cells with a significant correlation observed between disease activity and resting NK T cell CD69 expression(r = 0.55, p=.012).
A significant relationship was observed between NK cell percentage CD69 surface expression and serum IL-1β production(r= -0.72, p=0.01) and percentage CD25 and IL-8 production(r= -0.69, p=0.015) in SLE patients. NK T cell CD25 levels also showed significant correlation with both serum IL-6(r=0.63, p=0.032) and IFN-Y(r = 0.66, p=0.023).
Regarding responses to TLR ligands, TLR 7 stimulation resulted in a significant increase in both NK cell and NKT cell surface expression of CD69 and CD25 from the resting state in patients. In addition stimulation with all the TLR ligands resulted in increased NK Cell CD25 expression in SLE patients as compared to stimulated healthy controls, a result that was also seen following TLR 4 stimulation for NK T cell CD69 expression (8.7% v 3.9%, p = 0.005). Finally TLR 3 and TLR 9 stimulation resulted in a significant increase in NK T cell CD69 expression in patients compared to their resting state (TLR3 14.9% V 7.4%, p = 0.02)(TLR9 12.9% v 7.4%, p=0.008).
Conclusions Our results suggest that SLE patient NK cells and NK T cells are hyperactivated in their resting state compared to healthy controls with a significant relationship seen between resting NK T Cell CD69 expression and disease activity. Despite this baseline hyperactivated state SLE patients demonstrate increased responsiveness to TLR ligands.
Disclosure of Interest: None Declared