Infectious non-self recognition in invertebrates: lessons from Drosophila and other insect models

The vertebrate innate immune system recognizes infectious non-self by employing a set of germline-encoded receptors such as nucleotide-binding oligomerisation domain proteins (NODs) or Toll-like receptors (TLRs). These proteins are involved in the recognition of various microbial-derived molecules, including lipopolysaccharide (LPS), peptidoglycan (PGN) and beta1,3-glucan. Drosophila Toll receptors are not directly dedicated to non-self recognition and insect NOD orthologues have not yet been identified. Studies started more than 20 years ago and conducted on different insect models have identified other receptors on which invertebrate innate systems rely to sense invading microorganisms.