Functional role of CD40 and its ligand.

CD40, a cell surface receptor which belongs to the TNF-R family, was first identified and functionally characterized on B lymphocytes. In recent years, CD40 has been found expressed on other cells, including monocytes, dendritic cells, endothelial cells and epithelial cells and is now thought to play a more general role in immune regulation. The present paper reviews recent developments about CD40, with main emphasis on: (1) structure and expression of CD40 and its ligand; (2) CD40 signal transduction; (3) in vitro function of CD40 on different cell types, and (4) in vivo functions of CD40/CD40L interactions.