Involved in gastrointestinal immunity. Upon stimulation by muramyl dipeptide (MDP), a fragment of bacterial peptidoglycan, binds the proximal adapter receptor-interacting RIPK2, which recruits ubiquitin ligases as XIAP, BIRC2, BIRC3, INAVA and the LUBAC complex, triggering activation of MAP kinases and activation of NF-kappa-B signaling. This in turn leads to the transcriptional activation of hundreds of genes involved in immune response. Required for MDP-induced NLRP1-dependent CASP1 activation and IL1B release in macrophages. Component of an autophagy-mediated antibacterial pathway together with ATG16L1. Plays also a role in sensing single-stranded RNA (ssRNA) from viruses. Interacts with mitochondrial antiviral signaling/MAVS, leading to activation of interferon regulatory factor-3/IRF3 and expression of type I interferon.