Background/Purpose:

Interferon alpha (IFNα) is an inflammatory cytokine implicated in the development and persistence of autoimmunity.  Although IFNα expression is increased in a subgroup of SLE patients its role in other connective tissue diseases (CTDs) is less clear.  We aimed to characterise the IFNα signature across CTDs using 3 methods and determine whether in this mixed cohort we could identify common associations with clinical and laboratory features.

Methods:

Patients with at least 1 CTD clinical feature and at least 1 autoantibody were recruited.  Detailed clinical assessment was conducted and whole blood collected for RNA analysis and plasma for IFNα protein measurement by single molecule assay (SIMOA).

Interferon-stimulated gene (ISG) and nucleic acid receptors (NAR) expression was measured in whole blood using RT-qPCR.  The ISG score was calculated as the mean expression of 6 ISGs (IFI27, IFI44L, IFIT1, ISG15, RSAD2, SIGLEC1) relative to HPRT1 and 18s.  The ISG score was classed as positive (ISG+) or negative (ISG-) using the mean +2 SD of healthy controls.  6 NARs were measured: DDX58, MB21D1, TMEM173, TLR3, TLR7 and TLR9.  Expression of 30 ISGs was also explored using the NanoString customer designed codesets in a subgroup of patients.

Results:

We recruited 164 patients covering 6 diseases; SLE, Sjogren’s syndrome (SS), undifferentiated and mixed CTD (UCTD, MCTD), inflammatory myopathy (IIM) and systemic sclerosis (SSc).  63/164 (38%) of patients were ISG+ (figure).  NanoString (27 patients) and was strongly correlated with the IFN score (r=0.96).  Similarly 39/93 (41%) had plasma IFNα protein levels <10fg/ml (correlation for the 2 methods, r=0.83, p<0.001).

There were no differences in mucocutaneous or internal organ involvement between ISG+ and ISG- patients.  ISG+ patients had increased prevalence of rheumatoid factor, anti-Sm and -chromatin antibodies after adjusting for disease type. 

ISG+ patients had increased frequency of ever having a haematological disorder (as per the ACR SLE criteria) and in models adjusted for disease type, lower lymphocyte and neutrophil counts.

Expression of TLR7, TLR9, DDX58, MB21D1 and TMEM173 (but not TLR3) was increased in CTD compared to HC (all p<0.001).  Only DDX58 was positively associated with the ISG score (r=0.6556) and was increased in patients who were anti-ENA or anti-chromatin positive.  Anti-Ro was associated with reduced expression of all NARs (except DDX58); this association remained after adjustment for age, gender, disease group and ISG score.

Conclusion:

IFNα is increased in a subgroup of CTD patients but more strongly associates with haematological abnormalities than any disease subtype.   Increased NAR expression does not correlate with increased IFNα suggesting that the drivers of IFNα may be multifactorial.  The identification of this high-IFN subset of patients within a CTD cohort supports a pathology-based approach to treatment.

Figure