Background: IFN-alpha is a primary pathogenic factor in SLE, however the differences in cellular immunity between SLE patients with high vs. low IFN remains largely unknown. In this study, we characterized the IFN-high and IFN-low subgroups in human SLE by studying the stimulated cytokine responses post whole blood stimulation by Toll-like receptor (TLR) agonists.
Methods: SLE patients (n= 31) meeting ACR criteria for SLE and healthy controls (n=10) were recruited. Serum IFN was measured using a functional assay, and used to categorize patients as high vs. low. Whole blood was dispensed into tubes coated with the TLR agonists LPS, CpG and R848 (Tru-Culture.) Cytokine production in patient sera and after whole blood TLR stimulation was measured by bead-based multiplex assay or functional assays.
Results: Principal component analysis examining cytokine levels as a whole in SLE patients identified distinct clusters according to serum IFN activity, supporting the idea that high vs. low IFN status was a major influence on overall cytokine production in stimulated cells. IFN-high patients responded more dramatically to the TLR-4 agonist LPS than IFN-low (p<0.05), and controls (p=0.05). Post TLR-4 stimulation, IFN-high patients produced more CXCL9 (p=0.025), and less IL-12 (p=0.015) and VEGF (p=0.015) than IFN-low patients. In the IFN-low group, very different cytokine clusters emerged featuring IL-17. For example; IL-17 was strongly co-expressed with IL-4 and IL-5 (p<0.0001).
Conclusions: We have observed novel biologic differences between IFN-high and low SLE subgroups. IFN-high patients are significantly more responsive to TLR4 stimulation and produce a distinct inflammatory cytokine profile post TLR4 stimulation compared to IFN-low SLE.