Abstract
OBJECTIVE: Antiphospholipid syndrome (APS) is a thromboinflammatory disorder characterized by clinical and mechanistic heterogeneity that complicates early diagnosis and hinders targeted treatment. We aimed to identify distinct molecular endotypes among antiphospholipid antibody (aPL)-positive patients using whole-blood transcriptomics. METHODS: Whole-blood RNA sequencing was performed on 174 aPL-positive patients, including those with primary APS (n = 102), secondary APS (n = 29), and aPL positivity without classifiable APS (n = 43). Unsupervised machine learning and immune cell deconvolution defined transcriptomic clusters and immune landscapes. RESULTS: Four transcriptionally distinct clusters were identified. At one end of the spectrum, cluster 1 showed up-regulation of ribosomal and metabolic pathways and down-regulation of mechanistic target of rapamycin (mTOR), NETosis, and Hippo/interleukin-6 (IL-6) signaling. In contrast, cluster 4 exhibited the opposite pattern, with strong up-regulation of mTOR, NETosis, and Hippo/IL-6 signaling. Cluster 2 demonstrated modest enrichment in messenger RNA processing and amino acid metabolism, and cluster 3 showed biosynthetic suppression with mild Hippo/IL-6 activation. Clinically, cluster 4 stood out with higher IgG anticardiolipin and anti-β(2)-glycoprotein I positivity, elevated neutrophil counts, and increased urine protein-to-creatinine ratios. Immune deconvolution revealed distinct cell type profiles: cluster 1 was lymphoid predominant; cluster 2 had a balanced composition; cluster 3 was enriched in Treg cells, natural killer cells, macrophages, mast cells, and memory B cells; and cluster 4 was dominated by myeloid cells, including neutrophils, eosinophils, and dendritic cells. Distinct immune pathway activations were linked to clinical features, including white matter lesions, seizures, and cardiac valve disease. CONCLUSION: This study reveals four endotypes of aPL-positive patients, a step toward personalized medicine for APS through pathway-informed stratification and therapy.