Integrated Bulk and Spatial Proteomics of Castleman Disease: Molecular Signatures Across Subtypes and Compartmentalized Pathogenic Networks in Idiopathic Multicentric Castleman disease (iMCD)-Thrombocytopenia, Anasarca, Fever, Reticulin Fibrosis/Renal Dysfunction, and Organomegaly (TAFRO).

Castleman disease (CD) represents a heterogeneous group of lymphoproliferative disorders, with the idiopathic multicentric CD (iMCD) subtype associated with thrombocytopenia, anasarca, fever, reticulin fibrosis/renal dysfunction, and organomegaly (TAFRO) syndrome (iMCD-TAFRO) posing significant research challenges because of its severity and tissue scarcity. This study used integrated bulk and spatial proteomics to characterize protein expression profiles in lymph node samples across clinical and pathological subtypes. Bulk proteomics revealed subtype-specific molecular signatures, including distinct protein profiles for hyaline vascular vs plasmacytic variants, systemic complement activation distinguishing iMCD from unicentric CD, and molecular evidence supporting the classification of iMCD-idiopathic plasmacytic lymphadenopathy as a distinct entity. Specifically, iMCD-TAFRO exhibited upregulation of angiogenesis drivers (PDGFRβ and NOTCH3), interferon signaling proteins (STAT1/ISG15), and fibrosis markers (COL3A1/LOXL1). Spatial proteomics, through laser capture microdissection of follicular and vascular niches, delineated compartmentalized pathogenesis in iMCD-TAFRO. Intrafollicular vessels showed enrichment of myofibroblast markers (ACTA2) and programmed cell death regulators (eg, GSDMD and TFRC), whereas interfollicular regions displayed TGF-β/SMAD3-mediated upregulation of LOXL1 linked to fibrosis. Follicular zones demonstrated complement activation (CFHR1/CFHR2) and M2 macrophage infiltration. Our integrated approach delineated the molecular heterogeneity of CD, revealed spatially resolved pathogenic drivers in iMCD-TAFRO, and provided insights into its unique vascular-fibroinflammatory pathology, offering a foundation for advancing precision diagnostics and targeted therapies.