NFkB was identified as a sequence specific transcriptional activator that binds to the intronic enhancer of kappa light chain gene in B lymphocytes. NFkB is a heterodimer that consists of a 50 kDa DNA binding subunit (p50) and a 65 kDa transactivation subunit (p65/RelA). Both of these subunits exhibit sequence homology to the protooncogene c-Rel. The p50/p65 heterodimer remains in the cytosol in an inactive form as a complex with its inhibitor, IkB. Upon stimulation of cells by a wide variety of stimuli such as lipopolysaccharide (LPS), pro-inflammatory cytokines, and viral infection. IkB is phosphorylated and degraded by proteosome. The active NFkB heterodimer is translocated into the nucleus and induces gene expression.