In this review we focus upon recent advances in our understanding of the tissues and organs involved in host defence in C. elegans, as well as the virulence mechanisms employed by some pathogens to defeat those defences. A major advantage of C. elegans as a model system is its relatively simple anatomy. The C. elegans body plan is tubular, with the mouth at the

anterior end of the head and the anus at the posterior near the tail. The head contains the pharynx, a muscular organ that contracts rhythmically to pump food into the grinder, a chitinous rigid organ that crushes ingested material before it is pumped through the pharyngeal–intestinal valve into the lumen of the intestine [5]. The intestine proper, which takes up approximately one-third of the midbody transversal S1P Receptor inhibitor section, is a simple organ formed by just 20 non-renewable polarized LY2109761 molecular weight epithelial cells, organized in nine rings of directly apposed pairs of cells (except for the first ring, which is formed by four cells). These intestinal epithelial cells exhibit many ultrastructural similarities with mammalian intestinal epithelial cells, most conspicuously an apical brush border of microvilli protruding into the intestinal lumen. The microvilli are formed of actin bundles anchored in an intermediate filament terminal web. The intestine is metabolically

highly active, with similar functions to the fat body in flies and the liver in mammals [5]. Other major organs include the gonads, which fill up most of the transversal section Liothyronine Sodium of the animal and generate oocytes that are fertilized

as they pass through the spermathecae near the ventral uterus. Fertilized eggs remain inside the animal until early embryogenesis, at which point they are laid through the ventral vulval opening. The hypodermis (epidermis) and body wall muscle sheathe the intestine, the gonads and the body cavity (pseudocoelom). The body wall muscle contracts to generate the characteristic sinusoidal movements that allow locomotion and behaviour, co-ordinated by an intricate nervous system that links environmental sensory perception with movement, endocrine signalling and behaviour. The hypodermis, among other functions, deposits the highly impermeable cuticle, the collagenous exoskeleton of the worm. C. elegans lacks a circulatory system, professional immune cells and macrophage-like phagocytes. Being an invertebrate, it lacks antibody-generating adaptive immunity and relies on epithelial-based innate immunity for defence. Nevertheless, C. elegans mounts a sophisticated immune response, as measured by transcriptional regulation of host defence genes upon infection. In contrast to what is known about flies and mammals, the C. elegans immune response is mostly independent of Toll-like receptor (TLR) signalling [6,7].