Imd pathway

The Imd pathway is a broadly-conserved NF-κB immune signalling pathway of insects and some arthropods that regulates a potent antibacterial defence response. The pathway is named after the discovery of a mutation causing severe immune deficiency (the gene was named "Imd" for "immune deficiency"). The Imd pathway was first discovered in 1995 using Drosophila fruit flies by Bruno Lemaitre and colleagues, who also later discovered that the Drosophila Toll gene regulated defence against Gram-positive bacteria and fungi. Together the Toll and Imd pathways have formed a paradigm of insect immune signalling; as of September 2nd 2019, these two landmark discovery papers have been cited collectively over 5000 times since publication on Google Scholar.

Similarity to human signalling pathways

The Imd pathway bears a number of similarities to mammalian TNFR signalling, though many of the intracellular regulatory proteins of Imd signalling also bear homology to different signalling cascades of human Toll-like receptors.

Imd signalling in Drosophila

While the exact epistasis of Imd pathway signalling components is continually scrutinized, the mechanistic order of many key components of the pathway are well-established.

Imd pathway conservation in insects

The Imd pathway appears to have evolved in the last common ancestor of centipedes and insects. However certain lineages of insects have since lost core components of Imd signalling. The first and most famous example is the pea aphid Acyrthosiphon pisum.