Bugs fighting bugs: the evolution of the arthropod immune system.

Since the beginning of time, animals have needed to protect themselves from invaders. They primarily do so via their innate immune system, in which trained killer cells attack foreign pathogens – ranging from microscopic bacteria to macroscopic worms. While we know a fair amount about the innate immune system of most vertebrates and some insects, we know comparatively little about the immune system of arthropods. Here is where the new preprint by William Palmer and Francis Jiggins comes in.
Using the recently acquired sequences of multiple arthropod genomes, the authors characterized the immune systems of some pretty icky arthropods: the Water Flea, the Coastal Centipede, Chinese Scorpion, the House Spider, the Deer Tick, and the Western Orchard Predatory Mite, and the Red Spider Mite. Interestingly, the authors found:

… both remarkable diversification of the immune response across the arthropods, and unexpected conservation and similarities to mammalian genes… These include a group of arthropod toll-like receptors that share structural similarity with vertebrate TLRs and cluster with them phylogenetically.

This is important because it suggest that some components of the innate immune system, such as TLRs – which recognize foreign microbes and activate immune cell responses, have deep roots in our evolutionary history. The authors state:

Our results confirm an ancient origin for the innate immune system, predating the split between protostomes and deuterostomes. We find striking examples of conservation between vertebrates and arthropods, despite these two groups having diverged before the Cambrian explosion some 543 million years ago.

W. Palmer & F. Jiggins “Comparative genomics reveals the origins and diversity of arthropod immune systems” BioRxiv.
DOI: http://dx.doi.org/10.1101/010942