This chapter provides a short review of the immune system of urochordates, the closest living relative of vertebrates. Since adaptive immunity is a unique property of vertebrates, urochordates rely exclusively on innate immunity to recognize and eliminate pathogens. Here we discuss three...

Despite the lack of adaptive immunity based on gene rearrangement such as that in higher vertebrates, flies are able to defend themselves from a wide array of pathogens using multiple innate immune responses whose molecular mechanisms are strikingly similar to those of the innate immune...

Genetic studies have elegantly characterized the innate immune response in Drosophila melanogaster. However, these studies have a limited ability to reveal the biochemical mechanisms underlying the innate immune response. To investigate the biochemical basis of how insects recognize invading...

Bivalves are comprised of animals unclosed in two shell valves, such as mussels, oysters, scallops and clams. There are about 7,500 bivalve species and some of them are of commercial importance. Recently, interest in bivalve immunity has increased due to the importance in worldwide aquaculture...

This chapter provides a review of recent progress in the elucidation of innate immune mechanisms in crustaceans. Mainly due to the importance of crustacean aquaculture interest in this field is large and the subject for extensive research efforts. Here, we provide detailed data on the...

Lepidopteran insects provide important model systems for innate immunity of insects, particularly for cell biology of hemocytes and biochemical analyses of plasma proteins. Caterpillars are also among the most serious agricultural pests, and understanding of their immune systems has potential...

Earthworms belonging to oligochaete annelids became a model for comparative immunologists in the early sixties with the publication of results from transplantation experiments that proved the existence of self/nonself recognition in earthworms. This initiated extensive studies on the earthworm...

Horseshoe crab hemocyte selectively responds to bacterial lipopolysaccharides (LPS), which depends critically on the proteolytic activity of the LPS‑responsive serine protease zymogen factor C. In response to stimulation by LPS, the hemocyte secretes several kinds of immunocompetent...

A survey for immune genes in the genome for the purple sea urchin has shown that the immune system is complex and sophisticated. By inference, immune responses of all echinoderms may be similar. The immune system is mediated by several types of coelomocytes that are also useful as sensors of...

Throughout their lifetime, mosquitoes are exposed to pathogens during feeding, through breaks in their cuticle and following pathogen‑driven cuticular degradation. To resist infection, mosquitoes mount innate cellular and humoral immune responses that are elicited within minutes of exposure...

The phylum Cnidaria is one of the earliest branches in the animal tree of life providing crucial insights into the early evolution of immunity. The diversity in cnidarian life histories and habitats raises several important issues relating to immunity. First, in the absence of specific immune...

Ticks are blood feeding parasites transmitting a wide variety of pathogens to their vertebrate hosts. The vector competence of ticks is tightly linked with their immune system. Despite its importance, our knowledge of tick innate immunity is still inadequate and the limited number of...

The nematode Caenorhabditis elegans is proving to be a powerful invertebrate model to study host‑pathogen interactions. In common with other invertebrates, C. elegans relies solely on its innate immune system to defend itself against pathogens. Studies of the nematode response to infection...

Over their 500 million year history, gastropods have radiated into marine, freshwater and terrestrial environments and adopted life styles ranging from herbivory to carnivory to endoparasitism to symbiont‑mediated chemoautotrophy. They contend with many pathogens, including several lineages...

In the present chapter, we will emphasize the immune response in two compartments (Central nervous system and peripheral system) in two blood sucking leeches i.e., the medicinal leech and the bird leech Theromyzon tessulatum. In the medicinal leech, the neuroimmune response has been described...