GP2 (glycoprotein 2) is an intestinal M-cell transcytotic receptor essential for mucosal immunity and bacterial sensing. Localized at the apical membrane of M cells—specialized epithelial cells overlying gut-associated lymphoid tissue—GP2 specifically binds FimH, a protein component of type I pili on bacteria such as E. coli and S. typhimurium 1. Upon binding, GP2 internalizes piliated bacteria and delivers them across the intestinal epithelium to underlying lymphoid follicles, where dendritic cells capture them to initiate mucosal and systemic immune responses. This transcytotic function is conserved across species; zebrafish omcin genes (homologous to GP2) similarly confer resistance to bacterial infection 2. Beyond its primary immunological role, GP2 has emerged as a significant biomarker in disease contexts. NOX1 deficiency dysregulates M-cell differentiation, increasing GP2 expression in association with intestinal inflammation 3. Notably, GP2 plasma levels are independent predictive biomarkers for prostate cancer risk, with elevated expression detected 6 years before diagnosis 4. Additionally, GP2 gene variants at locus 16p12.3 show genome-wide association with pancreatic cancer susceptibility, particularly in East Asian populations, with functional evidence suggesting effects on KRAS activity 5. These findings position GP2 as both a critical immune receptor and an emerging clinical biomarker.