Essential for the imd/NF-kappa-B (Imd) humoral and epithelial immune response to Gram-negative bacteria (PubMed:7568155, PubMed:8808632, PubMed:11266367, PubMed:12433364). Functions as an adapter protein that transduces immunity signals from the activation of pathogen recognition receptors (PRRs) by bacterial infection to the Imd signaling pathway (PubMed:7568155, PubMed:11269502, PubMed:11703941, PubMed:12433364, PubMed:20122400). Binding of diaminopimelic acid-type (DAP-type) bacterial peptidoglycans (PGN) causes multimerization or clustering of PGRP receptors which activate the Imd cascade probably by recruiting imd, Fadd and Dredd to the receptor complex (PubMed:11269502, PubMed:12433364, PubMed:20122400). Once in proximity, Dredd cleaves imd in a Fadd-dependent manner to enable its association and activation by the ubiquitin E3-ligase DIAP2 (PubMed:20122400). The activated form of imd recruits and activates the Tab2/Tak1 complex thus acting upstream of the IKK complex (ird5 and key) to activate Rel and induce the expression of antimicrobial peptides such as Def, Dpt and Cecropin (PubMed:7568155, PubMed:8808632, PubMed:11703941, PubMed:12433364, PubMed:19837371, PubMed:20122400, PubMed:11266367). Also able to inhibit the viral replication of the Sindbis virus (PubMed:19763182). Involved in promoting the polyubiquitination and stability of faf which in turn, regulates the Imd pathway by controlling imd polyubiquitination and/or stability; they may therefore form a regulatory feedback mechanism within the Imd pathway (PubMed:23919485). Not required for the cuticle melanization immune response to bacterial challenge (PubMed:11266367). Interacts with Fadd (PubMed:12433364). Interacts with faf (PubMed:23919485). Interacts with Rpt6 (PubMed:25027767). Interacts (via N-terminus) with Usp2 (via N-terminus) (PubMed:25027767). Interacts (via N-terminus) with scny (via C-terminus) (PubMed:19837371). The N-terminally cleaved form interacts (via IAP-Binding motif) with Diap2 (via the BIR2 and BIR3 domains); the interaction promotes ubiquitination by Diap2 and the E2 ligases Uev1A, ben and Ubc5 (PubMed:20122400). Phosphorylated. Caspase-mediated cleavage is required for activation and function; upon immune stimulation, peptidoglycans (PGN) induce proteolytic cleavage by caspases such as Dredd leading to its ubiquitination. Ubiquitination is essential for function; after PGN-induced caspase-mediated cleavage the N-terminally cleaved imd interacts with the E3 ligase Diap2 leading to polyubiquitination of 'Lys-63'-linked chains involving the E2 complex members Uev1A, ben and Ubc5 (PubMed:20122400). These 'Lys-63' chains stabilize imd and may serve as scaffolds to recruit and activate the key kinases TAK1 and IKK (PubMed:20122400). Under normal unchallenged conditions, scny deubiquitinates the activating 'Lys-63'-linked chains to prevent signal transduction and this is also likely to promote the polyubiquitination of 'Lys-48'-linked chains which act as 'tags' for proteosomal degradation (PubMed:19837371). Usp2 then deubiquitinates the 'Lys-48'-linked chains and this promotes degradation of imd probably by allowing interaction between imd and the proteasome (PubMed:25027767). RNAi-mediated knockdown in the fat body results in reduced expression of the antimicrobial peptide gene Dpt following infection with E.coli. Extended N-terminus.