IkB-like protein that inhibits the binding of NF-kappa-B to DNA, thereby downregulating proinflammatory cytokine production (PubMed:8970976). Forms a heterodimer with the NF-kappa-B subunit RELA/p65 and prevents the activation of the NF-kappa-B transcription factor (By similarity). Inhibits calcineurin function, which is required for the induction of nuclear factor of activated T cells (NFAT)-dependent immune response genes (PubMed:23468591, PubMed:9677199). Prevents the binding of substrates to calcineurin without affecting the phosphatase activity (PubMed:23468591). Does not contain the serine residues that are phosphorylated by host IkB kinase and thus is not degraded following stimulation of the NFkB pathway (By similarity).