Tumor necrosis factor receptor 1 and 2 (TNF-R1 and TNF-R2) are 55 and 75 kDa. While TNF-R1 and TNF-R2 share 28% sequence homology in the extracellular domains, their intracellular domains lack sequence homology, sμggesting that they differ in their internal signal transduction pathways. TNF-R1 contains an approximately 80 amino acid death domain near its carboxy terminus capable of transmitting an apoptotic signal throμgh its interaction with TRADD (TNF-R1 associated death domain protein), and subsequent interactions with FADD. TNF-R1 can also activate the transcription factor NFkB via TRAF2 (TNF receptor associated factor 2). The cytoplasmic domain of TNF-R1 can directly interact with Jak kinase, thereby activating the JAK/STAT signal transduction cascade.