New SPAID Database Maps Hidden Autoantigens Behind Autoimmune Diseases

Autoimmune diseases, in which the immune system turns against the body’s own tissues, affect hundreds of millions of people worldwide and remain notoriously difficult to diagnose early and precisely. At the heart of every autoimmune response lies a molecular trigger: an autoantigen, a self-protein or peptide that the immune system mistakenly recognizes as foreign. Yet despite decades of research, the full landscape of these triggers remains incomplete, in part because scientists have traditionally focused only on canonical, well-annotated protein-coding genes. Now, a research team led by scientists at Sun Yat-sen University and collaborating institutions in China has unveiled SPAID, a comprehensive database designed to systematically catalog candidate autoantigens across 14 autoimmune disorders, including both canonical proteins and a vast, largely unexplored universe of non-canonical proteins translated from non-coding regions of the genome.

SPAID, which is freely accessible online at spaid.renlab.cn, organizes its evidence into two distinct levels. The first, a validated level, contains proteins carrying experimentally confirmed epitopes drawn from the Immune Epitope Database, supported by positive T-cell assays and major histocompatibility complex (MHC) ligand assays. The second, a proteomics-based level, aggregates disease-associated peptides and proteins identified through mass spectrometry from human patient samples, annotated with differential expression patterns, predicted immunogenicity scores, and functional features. This two-tier architecture allows researchers to distinguish between candidates backed by direct immunological experimentation and those flagged through high-throughput proteomic discovery that await laboratory validation.

The technical ambition behind SPAID is considerable. To capture non-canonical proteins, the team assembled candidate sequences from more than 660,000 non-coding RNA entries in RNAcentral and over 332,000 intronic sequences from the IntroVerse database. Each candidate was evaluated for coding potential using two independent algorithms, CPAT and CNCI, and only sequences passing both thresholds were retained. Open reading frames were then predicted with NCBI’s ORFfinder and translated into amino acid sequences, which were de-duplicated against the UniProt reference set. The result is a unified protein sequence space of 576,516 sequences, combining 42,444 canonical UniProt proteins with 534,072 non-canonical proteins, including 447,445 intron-derived and 86,627 ncRNA-derived candidates.

Onto this reference framework, the researchers mapped a wealth of experimental data. From 292 publications, they integrated T-cell and MHC ligand assay records, ultimately identifying 1,141 unique validated epitopes from 10 autoimmune diseases supported by 2,750 positive T-cell assay records, alongside 20,424 distinct epitopes from 21,566 positive MHC ligand assays across five diseases. In total, these experimentally supported epitopes mapped to 21,349 unique proteins, spanning 16,966 canonical, 1,681 intron-derived, and 2,702 ncRNA-derived proteins. The inclusion of non-canonical proteins at this level is particularly striking, as it suggests that proteins translated from non-coding RNAs and introns can serve as genuine immune targets in human autoimmunity.

The proteomics-based level is equally extensive. Drawing on public repositories including PRIDE, MassIVE.quant, jPOST, PeptideAtlas, and iProX, the team curated 675 human proteomic samples spanning 14 autoimmune diseases, stratified into 51 disease- and tissue-specific cohorts. Peptides were identified by searching tandem mass spectra against the unified sequence space using DIA-NN for data-independent acquisition datasets and MaxQuant for data-dependent acquisition, with stringent false discovery rate control of 1 percent at the peptide-spectrum match, peptide, and protein-group levels. This rigorous filtering was essential because non-canonical peptides carry a heightened risk of false-positive identification. The search yielded 176,363 mass spectrometry-identified peptides assigned to 26,085 disease-associated proteins, including 927 ncRNA-derived and 531 intron-derived proteins.

To transform raw protein identifications into biologically meaningful signals, SPAID performs differential expression analysis for each cohort, comparing disease samples against matched controls. Proteins were classified as disease-only detected, upregulated, downregulated, or other, and results across multiple cohorts were integrated using Robust Rank Aggregation to assess cross-study consistency. Across the 14 diseases, the platform identified 4,577 disease-only detected proteins, 2,571 significantly upregulated proteins, and 757 significantly downregulated proteins. Notably, the disease-only category included 193 ncRNA-derived and 28 intron-derived proteins, demonstrating that non-canonical translation products participate in disease-specific proteomic signatures rather than representing background noise.

One of the most consequential questions the team addressed was whether these non-canonical proteins are reproducible. In diseases supported by at least three independent proteomic cohorts, more than 40 percent of non-canonical proteins were repeatedly detected: 61.51 percent in psoriasis, 54.58 percent in systemic lupus erythematosus, 51.41 percent in Crohn’s disease, and 40.32 percent in rheumatoid arthritis. Even more striking, among the repeatedly detected proteins, expression patterns showed remarkable concordance, with 99.33 percent consistency in rheumatoid arthritis, 93.93 percent in lupus, and 87.72 percent in psoriasis. Cross-referencing with published literature revealed that only 1.10 percent of the 1,458 non-canonical proteins identified across the diseases had prior experimental support, meaning the overwhelming majority represent previously unrecognized translation products now documented at scale for the first time.

To pinpoint which of these proteins might actually provoke immune responses, SPAID incorporates an immunogenicity prediction pipeline. Every mass spectrometry-detected peptide was segmented into overlapping 8- to 14-mer fragments and evaluated for HLA class I presentation across 12 functional supertypes, integrating MHC binding affinity, peptide-MHC stability, and T-cell recognition probability. Candidates were then refined using PanPep, a machine-learning tool that estimates T-cell receptor interaction probabilities against a panel of 419 CDR3 sequences. Overall, 14.70 percent of the 176,363 detected peptides were classified as putatively immunogenic, mapping to 15,558 immunogenic proteins, or 59.64 percent of all disease-associated proteins in the database. Immunogenic candidates were strongly enriched among disease-only detected proteins, representing 69.24 percent of that subset, consistent with the idea that proteins elevated under inflammatory conditions feed the antigen-processing machinery that can expose sequestered self-determinants and cryptic epitopes.

By intersecting three features, disease-specific proteomic detection, predicted immunogenicity, and experimental epitope support, the team defined a high-confidence core set of 2,023 candidate autoantigens. The platform’s practical utility was then demonstrated in an independent rheumatoid arthritis cohort, where serum proteomics of five patients and five healthy controls identified 1,559 proteins, 132 of which were RA-associated. A two-step validation pipeline using SPAID recovered clinically established biomarkers such as gamma-interferon-inducible protein 16 (IFI16) and immunoglobulin mu heavy chain, while also flagging novel candidates. Nine proteins, including myosin-9 (MYH9), glutathione S-transferase P (GSTP1), and hemoglobin subunit gamma-1/2 (HBG1/2), harbored experimentally validated epitopes. APOA4, apolipoprotein A-IV, emerged as an entirely novel candidate with highly specific enrichment in RA samples and strong predicted immunogenicity but no prior literature link to the disease, illustrating how the database can surface unexpected therapeutic leads.

Beyond its scientific content, SPAID offers a polished web interface built on a MySQL backend with a Java-based server and interactive ECharts visualizations. Users can search by disease, tissue, or protein attributes, run BLAST searches against transcript, protein, and peptide datasets, and explore hierarchical gene, protein, and peptide pages featuring expression boxplots, volcano plots, 3D structural models from the Protein Data Bank or ColabFold, predicted post-translational modification sites generated with PTM-Mamba, and an MS/MS spectrum annotator. The authors are candid about limitations: immunogenicity predictions currently cover only HLA class I, omitting CD4 T-cell biology tied to HLA class II, and the underlying proteomic data skew toward accessible tissues such as blood and skin. Mass spectrometry, however stringent, cannot on its own prove functional translation or physiological epitope presentation. Positioned as a candidate discovery resource rather than a definitive catalog, SPAID nonetheless represents a foundational shift in how autoantigen research can be conducted, and its developers plan future expansions to include HLA class II data and broader tissue proteomics, potentially accelerating diagnostics and targeted therapies for millions of autoimmune patients.

Subject of Research: A comprehensive database for disease-specific autoantigen discovery in autoimmune disorders

Article Title: SPAID: a comprehensive database for disease-specific autoantigens in autoimmune disorders

Article References: Deng, S., Wei, F., Pang, Y., Zhang, L., Zhi, S., Chen, T., Zuo, Z., Ren, J., Xie, Y., & Luo, X. (2026). SPAID: a comprehensive database for disease-specific autoantigens in autoimmune disorders. Advanced Biotechnology, 4(2), Article 23. https://doi.org/10.1007/s44307-026-00117-8

Image Credits: AI Generated

DOI: 10.1007/s44307-026-00117-8

Keywords: autoimmune diseases, autoantigens, SPAID database, proteomics, non-canonical proteins, mass spectrometry, epitopes, HLA class I, immunogenicity prediction, rheumatoid arthritis, biomarker discovery, protein databases