CXCL13 is an activity marker for systemic, but not cutaneous lupus erythematosus: a longitudinal cohort study.

Serum levels of the IFN-regulated cytokine CXCL13 have been found to correlate with SLEDAI and renal involvement in systemic lupus erythematosus. This study investigates whether CXCL13 can also be a marker of disease activity in patients with subacute cutaneous or chronic cutaneous lupus erythematosus (SCLE, CCLE). We analysed CXCL13 levels in 60 patients' sera (18 SLE, 19 SCLE, 23 CCLE) at five time points within 1 year and correlated these levels with disease activity scores and laboratory markers. Clinical scores with no/mild, moderate or high/severe disease activity were categorized by SLEDAI in SLE, by CLASI in SCLE/CCLE. CXCL13 levels were significantly higher in SLE (median 122.5, IQR 88.0-239.0 pg/ml) than in CCLE patients (median 69.0, IQR 60.0-102.0 pg/ml) (p = 0.006). CXCL13 levels were elevated in 59% (41/70) of SLE patient visits with mild or no disease activity, but in 90% (9/10) with high disease activity. CXCL13 levels correlated with ECLAM, dsDNA-antibodies, and inversely with complement factors C3 and C4 in SLE, and with IgA and ESR in SCLE. In CCLE CXCL13 did not correlate with CLASI or laboratory markers. One SCLE and two CCLE patients with CXCL13 levels > 500 pg/ml had conversion to SLE or an underlying autoimmune disease. CXCL13 seems to be a useful marker of disease activity in SLE, but not in SCLE and CCLE. Conversion from normal to elevated CXCL13 may indicate a flare of SLE. Whether high CXCL13 levels in cutaneous LE indicate the development of SLE should be further investigated.