CD46 (membrane cofactor protein) is a ubiquitously expressed complement regulatory protein that serves multiple critical biological functions. As a primary function, CD46 acts as a cofactor for factor I-mediated inactivation of complement components C3b and C4b, protecting host cells from complement-mediated damage 1. Beyond complement regulation, CD46 modulates T cell immunity through positive regulation of T cell proliferation, regulatory T cell differentiation, and memory T cell formation [GO annotations]. Structurally, CD46 comprises four short consensus repeats (SCRs) in its extracellular region, with alternatively spliced isoforms generating tissue-specific variants 12. CD46 functions as a viral and bacterial entry receptor, earning designation as a "pathogen magnet" 3. Vaccine-adapted measles virus strains utilize CD46 as an alternative receptor through H protein amino acid substitutions 45. Additionally, CD46 facilitates entry of human cytomegalovirus in trophoblasts and certain epithelial cells 6, mediates human herpesvirus-6A infection through gQ1/gQ2 glycoproteins 7, and serves as a receptor for human adenovirus 26 via hexon protein binding 8. Clinically, CD46 dysfunction associates with atypical hemolytic uremic syndrome type 2. Recently, elevated CD46 expression correlates with malignant transformation and metastatic potential, positioning it as a cancer therapeutic target 3.