Objectives

In response to the urgent unmet needs of heterogeneity, unpredictability, and diagnostic delay in systemic lupus erythematosus (SLE), we aimed to identify and validate new immunoglobulin (Ig)G and IgA autoantibody specificities.

Methods

Using a KoRectly EXpressed technology-based microarrays (i-Ome Discovery; Sengenics), we screened for circulating IgG and IgA autoantibodies against 1609 proteins in 2 independent cohorts (discovery: NTC02890121; validation: NCT02890134) comprising patients with SLE (n = 199 and n = 30), primary Sjögren's disease (n = 115 and n = 31), and systemic sclerosis (n = 115 and n = 24), and healthy controls (HCs; n = 111 and n = 84), respectively.

Results

We identified and validated 5 IgG (anti-Lin-28 homolog A [LIN28A], anti-HNRNPA2B1, anti-HMG20B, anti-HMGB2, and anti-alpha-globin transcription factor CP2 [TFCP2]) and 4 IgA (anti-LIN28A, anti-HMG20B, anti-SUB1, and anti-TFCP2) autoantibodies that demonstrated high specificity for SLE (0.91-0.94), along with consistent and robust positivity (0.22-0.69) in differentially abundant autoantibody (daAAb) analysis between SLE and comparator groups. IgG and IgA anti-LIN28A levels varied over a 14-month follow-up in the validation cohort of newly diagnosed patients with SLE and exhibited metrics that outperformed those of traditional autoantibody markers such as anti-double-stranded DNA. Clustering of patients with SLE based on autoantibody positivity (levels above the HC median plus 2 IQRs in the discovery cohort) status revealed 1 subgroup demonstrating seroreactivity against multiple antigens, 3 exhibiting varying reactivity, and 1 showing no reactivity. In pathway analysis, daAAb targets pointed to DNA-binding and RNA-binding and transcription functions.

Conclusions

Novel autoantibodies validated in this study may enhance diagnostics and molecular characterisation in SLE. The prominent IgA seroreactivity implicates important roles of mucosal tissues in SLE autoimmunity, warranting further investigation.