The role of innate lymphoid cells (ILCs) in the pathophysiology of rheumatic diseases is emerging. Evidence from animal studies implicate type I IFN, produced by plasmacytoid dendritic cells, to be involved in regulating the survival of group 2 and group 3 ILCs (ILC2s and ILC3s) via the upregulation of Fas (CD95) expression. For the first time, we explored the frequency and phenotype of circulating ILCs in SLE and primary Sjögren's syndrome (pSS) in relationship to the IFN signature.
Frequencies and phenotypes of ILC subsets and plasmacytoid dendritic cells were assessed by flow cytometry in peripheral blood of patients with SLE (n = 20), pSS (n = 20) and healthy controls (n = 17). Patients were stratified by the presence or absence of an IFN signature as assessed by RT-qPCR on circulating mononuclear cells.
ILC1 frequencies were increased in peripheral blood of patients with SLE as compared with healthy controls and correlate with disease activity in pSS patients. Overall, the frequencies of ILC2s or ILC3s did not differ between patients with SLE, pSS and healthy controls. However, patients with a high type I IFN signature expressed elevated levels of Fas on ILC2s and ILC3s, which coincided with decreased frequencies of these cells in blood.
The presence of a type I IFN signature is related to Fas expression and frequencies of circulating ILC2s and ILC3s in patients with SLE and pSS, potentially altering the homeostatic balance of ILCs.