Cell-specific regulation of the CD21 gene

The Complement Receptor Type 2 (Cr2-145,CR2, CD21) is an important receptor in the innate and acquired immune response. CD21 is produced by B cells an d follicular dendritic cells, where it binds cleavage products of the C3 co mplement protein. CD21 facilitates internalization of immune complexes by B cells to enhance antigen presentation. CD21. in association with CD19/CD81 , also serves as a coaccessory activation complex with the B-cell antigen r eceptor, permitting a lower antigen concentration to achieve maximal B-cell activation. CD21 traps immune complexes on the surface of follicular dendr itic cells and displays them to activated B cells in germinal centers. Much work has been conducted to determine the transcriptional control mechanism s dictating CD21 expression. Appropriate transcriptional control of the CD2 1 gene evidently requires the CD21 promoter, as well as intronic sequences with enhancer and suppressor functions. Chromatin structure has been implic ated in regulating the coordination of CD21 promoter and intronic control s equences by regulating access to them by putative transcription Factors. Th is review assesses the past and current research into CD21 transcriptional regulation and offers insight into future experimental directions. (C) 2001 Elsevier Science B.V. All rights reserved.