A CYTOTOXIC CD40 P55 TUMOR-NECROSIS-FACTOR RECEPTOR HYBRID DETECTS CD40 LIGAND ON HERPESVIRUS SAIMIRI-TRANSFORMED T-CELLS/

The B cell activation molecule CD40 and the p55 tumor necrosis factor receptor (p55TNFR) belong to the same family of structurally conserved proteins. We constructed a chimeric receptor consisting of the CD40 e xtracellular and transmembrane domains and the p55TNFR intracellular d omain. This receptor hybrid retained the biological activity and the l igand specificity of the respective wild-type receptor domains. Thus i t exerted a marked cytotoxic effect in three different transfected cel l. lines after activation not only with anti-CD40 antibody but also wi th CD40 ligand (CD40L) in soluble and membrane-bound forms. Using hybr id-transfected baby hamster kidney cells we demonstrated that herpesvi rus saimiri-transformed human CD4(+) T lymphocytes constitutively expr ess bioactive CD40 ligand on their surface. The hybrid receptor-based assay was highly specific for CD40 activating reagents and more sensit ive than an assay measuring CD40-mediated B cell rescue from apoptosis . Hence CD40/p55TNFR transfectants may be useful for dissecting CD40L- mediated events in T-B cell interactions, and also to detect a defecti ve CD40L molecule in putative hyper-IgM syndrome patients.