Table 2.

Correlations between IFN scores and serum KYN/TRP pathway metabolite levels in subjects with SLE according to ISG expression subgroup

ISG expression subgroup	IFN score method (z-scores)	KYN/TRP (rs)	P value	QA/KA (rs)	P value
IFN high (n=36)	ISG-A	0.490	0.002*	0.129	0.453
	19 type I ISG	0.487	0.003*	0.216	0.205
IFN low (n=23)	ISG-A	−0.174	0.427	−0.286	0.187
	19 type I ISG	0.269	0.215	−0.210	0.335
IFN similar to HC(n=13)	ISG-A	0.170	0.578	−0.126	0.681
	19 type I ISG	0.242	0.426	0.000	1.000

Subjects with SLE were assigned to one of three subgroups: ‘IFN high’ (Z-IFN score ≥SD above HC mean), ‘IFN low’ (Z-IFN score ≥1 to <2) or ‘IFN similar to HC’ (Z-IFN score <1). In each subgroup, correlations between IFN scores (derived from ISG-A and the 19 type I ISG) and metabolite ratios are displayed.

*Remained significant after Benjamini-Hochberg correction for multiple comparisons.

HC, healthy control; IFN, interferon; ISG, interferon-stimulated gene; KA, kynurenic acid; KYN, kynurenine; QA, quinolinic acid; r_s, Spearman correlation; TRP, tryptophan.