Single-Cell RNA Sequencing of Terminal Ileal Biopsies Identifies Signatures of Crohn's Disease Pathogenesis.

Crohn’s disease (CD) is a chronic inflammatory bowel disease exhibiting substantial heterogeneity in clinical presentation and response to therapy. To explore its molecular basis, we developed IBDverse, the largest single-cell RNA sequencing (scRNA-seq) dataset of terminal ileal biopsies, profiling over 1.1 million cells from 111 CD patients and 232 healthy controls. This resource integrates discovery and replication cohorts for robust identification of CD-associated cell types, genes, and pathways. We uncovered epithelial changes marked by interferon-driven MHC-I upregulation, persisting in progenitors after macroscopic inflammation resolution. ITGA4+ macrophages were identified as key inflammatory drivers, showing enriched JAK/STAT signaling and cytokine expression (IL-6, IL-12, IL-23). Heritability analysis linked inflammatory monocytes and macrophages to CD susceptibility, implicating resident and recruited immune cells in pathogenesis. These findings establish a comprehensive cellular and molecular framework for CD, offering new insights into disease mechanisms and therapeutic opportunities.