The I-kappa-B-kinase (IKK) complex, a key regulator of the nuclear factor kappa B (NF-kB) signaling pathway, consists of two catalytic subunits, IKBKA (KKα or CHUK) and IKBKB (IKKβ), associated with a regulatory subunit IKBKG (NEMO). The IKK complex is responsible for the phosphorylation of inhibitors of NF-kB (IkBs), such as NFKBIA or NFKBIB. Once phosphorylated, IkB undergoes ubiquitin-mediated degradation, releasing the transcription factor NF-kB thereby allowing translocation of NF-kB to the nucleus to regulate gene expression (Oeckinghaus A and Ghosh S 2009). NOD-like receptor C5 (NLRC5), the transcriptional activator of genes coding for MHC-I, has been implicated in the regulation of inflammatory pathways and IFN-dependent antiviral defense (Benko S et al. 2010; Cui J et al. 2010). Overexpression of NLRC5 inhibited NFkB-luciferase reporter activity in human embryonic kidney 293T (HEK293T) cells treated with interleukin (IL)-1β, TNF-α or toll-like receptor (TLR) agonists such as bacterial LPS (TLR4 ligand) or R848 (TLR7/8 ligand) (Cui J et al. 2010). Similar findings were obtained with human monocytic THP-1 cells and murine embryonic fibroblasts (MEFs) (Cui J et al. 2010). Further, NLRC5 deficiency resulted in enhanced phosphorylation of IKBKB, CHUK, and increased expression of NF-kB-responsive cytokines (such as TNF-α and IL-6), in LPS-stimulated THP-1 and mouse macrophage RAW264.7 cells (Cui J et al. 2010). NLRC5 deficiency enhanced NF‐kB activation in mouse cells in response to TLR3, TLR4, TLR7, TLR9 ligands (Tong Y et al. 2012) and TLR2 ligand (Wang M et al. 2019). Knockdown of NLRC5 also enhanced cytokine response and antiviral immunity in vesicular stomatitis virus (VSV)-treated primary human monocytes, primary murine macrophages and RAW264.7 cells. Studies with NLRC5-deficient mice confirmed the regulatory role of NLRC5 in the induction of NF-kB and type I interferon in response to LPS or VSV infection (Tong Y et al. 2012). Moreover, NLRC5 co-immunoprecipitated with IKBKA (CHUK) and IKBKB subunits, but not with IKBKG, upon co-expression of tagged proteins in HEK293T cells (Cui J et al. 2010). Mutagenesis analysis revealed that human NLRC5 targets the amino-terminal kinase domain (KD) of IKBKB. Fractionation of RAW264.7 cells extracts on a size-exclusion column followed by immunoblotting analysis showed that both CHUK:IKBKB:IKBKG and CHUK:IKBKB:NLRC5 complexes co-exist in unstimulated cells suggesting that NLRC5 inhibits the interaction between IKBKG (NEMO) and IKBKB/CHUK (Cui J et al. 2010). The dynamics of NLRC5 interaction with IKBKB/CHUK upon stimulation is regulated by TRAF2/TRAF6-dependent ubiquitination of NLRC5 (Meng Q et al. 2015). These data suggest that NLRC5 negatively regulates NF-kappa-B activation via targeting IKBKB and CHUK.