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Objectives: Type 1 interferon (IFN) is key to the pathogenesis of SLE, evidenced by the expression of IFN-stimulated genes (ISGs) in most patients, but the clinical utility of serial ISG assessment remains unknown. With the emergence of IFN-blocking drugs, we aimed to examine IFN status in relation to clinical findings longitudinally to provide insights into the value of testing ISG levels over time., Methods: Clinical data and whole blood were collected prospectively on adult patients with SLE from a single tertiary lupus centre. IFN status was measured using a panel of ISGs., Findings: 729 samples were analysed from 205 patients. At baseline, 62.9% of patients were IFN high, 30.2% IFN low and 6.8% borderline. 142 patients had multiple samples collected, and 87.3% of these demonstrated stable ISG status over time. In longitudinal follow-up, IFN high patients had higher activity in multiple organ domains and spent less time in Lupus Low Disease Activity State, but IFN score did not correlate with SLE Disease Activity Index in individual patients. In the small subset of patients who had large fluctuations in ISG across the observation period, most had high-dose glucocorticoids that correlated with ISG suppression. However, low-moderate-dose glucocorticoids did not suppress ISG expression., Conclusion: Although IFN high status is associated with indicators of more severe SLE, in the majority of patients, ISGs are stable across time and do not correlate with disease activity. Changes in ISG expression may be seen with high-dose, but not routine dose, glucocorticoid exposure. These findings suggest baseline but not serial ISG measurement may be of value in the management of SLE., Competing Interests: Competing interests: Outside the scope of this work, EM has received consulting fees from AbbVie, AstraZeneca, Amgen, Biogen, Bristol Myers Squibb, Eli Lilly, EMD Serono, Genetech, Janssen, Servier and UCB, and research grants from AbbVie, AstraZeneca, Bristol Myers Squibb, Eli Lilly, EMD Serono and Janssen. AH has received research grants from AstraZeneca, Merck and BMS., (© Author(s) (or their employer(s)) 2022. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

Type I interferon (IFN) pathways are significant in SLE pathogenesis. Less is known about the utility of measuring markers of IFN activity in patients, or whether patient subsets with different profiles exist. We explored the longitudinal associations of IFN-induced chemokines with disease activity in a cohort of SLE patients. We calculated a validated composite score (IFN-CK) of three type I IFN-inducible chemokines (CCL2/CXCL10/CCL19) measured in 109 SLE patients (median 7 occasions over 3.2 years). Longitudinal associations of IFN-CK score with disease activity (SLEDAI-2K) and other variables were assessed using general estimating equation (GEE) methods. IFN-CK was detectable in all patients. SLEDAI-2K was significantly associated with IFN-CK, damage score and prednisolone dose. SLEDAI-2K remained significantly associated with IFN-CK over time after adjustment of covariates. Patients with high time-adjusted mean IFN-CK had lower complement and higher time-adjusted disease activity. Concordance between IFN-CK and SLEDAI-2K varied widely among patients, with some individuals having none, others weak, and a subset very high concordance. In summary in our cohort of SLE patients, serum IFN-CK varied over time with disease activity, but with wide variation in concordance. Differing relationships between IFN pathway activation and disease activity may be valuable in assigning patients to emerging IFN-pathway targeting treatments.

Ethnicity is a key factor impacting on disease severity in SLE, but molecular mechanisms of these associations are unknown. Type I IFN and MIF have each been associated with SLE pathogenesis. We investigated whether increased SLE severity in Asian patients is associated with either MIF or Type I IFN. SLE patients (n = 151) had prospective recording of disease variables. Serum MIF, and a validated composite score of three Type I IFN-inducible chemokines (IFNCK:CCL2, CXCL10, CCL19) were measured. Associations of MIF and IFNCK score with disease activity were assessed, with persistent active disease (PAD) used as a marker of high disease activity over a median 2.6 years follow up. In univariable analysis, MIF, IFNCK score and Asian ethnicity were significantly associated with PAD. Asian ethnicity was associated with higher MIF but not IFNCK score. In multivariable logistic regression analysis, MIF (OR3.62 (95% CI 1.14,11.5), p = 0.03) and Asian ethnicity (OR3.00 (95% CI 1.39,6.46), p < 0.01) but not IFNCK were significantly associated with PAD. These results potentially support an effect of MIF, but not Type I IFN, in heightened SLE disease severity in Asian SLE. The associations of MIF and Asian ethnicity with PAD are at least partly independent.