The CD40 (HI40a) antibody recognizes a 48-kDa type-I single chain transmembrane glycoprotein e, Xenopus/Amphibian,pressed on normal and neoplastic B cells, but not on terminally differentiated plasma cells. CD40 antigen is also present on Hodgkin and Reed-Sternberg cells, follicular dendritic cells, some macrophages, basal epithelial cells and endothelial cells. The ligand for CD40 is CD154 (CD40L). CD40 is involved in growth, differentiation, isotype-switching on B cells and rescuing B cells from apoptosis.