The immune deficiency (Imd) pathway primarily mediates the humoral immune response to Gram-negative bacteria. Activation of the Imd pathway by diaminopimelic acid-type peptidoglycan initiates a signaling cascade that ultimately results in the release of the NFκB-like factor Rel from auto-inhibition and its translocation into the nucleus to activate the transcription of antimicrobial peptides. (Adapted from FBrf0224587 and FBrf0238555.)