BACKGROUND: There is increased expression of type I interferon (IFN)-regulated 
proteins in the blood and target tissues of patients with cutaneous lupus 
erythematosus (CLE) and systemic lupus erythematosus (SLE). Patients with SLE 
have increased IFN-regulated gene expression pointing towards a possible 
underlying genetic defect.
OBJECTIVES: To determine expression levels of five type I IFN-regulated genes 
that are highly expressed in SLE in the peripheral blood of patients with CLE 
and to correlate the expression levels with cutaneous disease activity.
METHODS: Peripheral blood was obtained from 10 healthy controls and 30 patients 
with CLE, including eight with concomitant SLE. Total RNA was extracted and 
reverse transcribed into complementary DNA. Gene expression levels were measured 
by real-time polymerase chain reaction. Gene expression was normalized to GAPDH, 
standardized to healthy controls and then summed to calculate an IFN score for 
each patient. Disease activity was assessed with the Cutaneous Lupus Area and 
Severity Index (CLASI).
RESULTS: Patients with subacute CLE (SCLE) and discoid lupus erythematosus (DLE) 
had elevated IFN scores compared with healthy controls regardless of concomitant 
SLE (P < 0·01 with SLE and P < 0·05 without SLE). There was no difference 
between patients with tumid lupus erythematosus (TLE) and healthy controls. The 
IFN score correlated with CLASI scores (Spearman's rho = 0·55, P = 0·0017).
CONCLUSIONS: Patients with SCLE and DLE have an IFN signature, as seen in SLE. 
The level of gene expression correlates with cutaneous disease activity. These 
findings support a shared pathogenesis between SLE and some subtypes of CLE.