Immune Response of Molluscs

Abstract

In common with other invertebrates, molluscs are known to have internal immune response against foreign particles and organisms. The innate immunity of molluscs reflects the inherent non-specific response that provides the first line of defense. Anatomic barriers, phagocytic cells, and physiological components are the main elements of the innate immune response in molluscs. It is composed of both cellular and humoral elements. The cellular components are the circulating hemocytes. Small invaders are eliminated by the phagocytic hemocytes, while large invaders are eliminated by encapsulation. The ingested foreign particles are then hemolyzed by the action of certain toxic enzymes that catalyze oxidative burst reactions capable of killing pathogens and foreign invaders. Humoral components of molluscan immunity involve nitric oxide, lysozyme activity, lectins, and the phenyloxidase system. The current chapter sheds light on the elements of the molluscan innate immune system and presents a case study of the immune response of Lymnaea stagnalis mollusc against Chaetogaster limnaei parasite. The effect of the parasite on some humoral immune response parameters such as nitric oxide, phenol oxidase, and lysozyme production was investigated. In conclusion, the snail Lymnaea stagnalis exerts humoral immune response against Chaetogaster limnaei parasite. However, this response is insufficient to eliminate the parasite.

Ancestral Physical Stress and Later Immune Gene Family Expansions Shaped Bivalve Mollusc Evolution

“…This is consistent with the previous genomics and molecular biology studies highlighting the significance of HSPs in bivalves for maintaining cellular function during exogenous redox/chemical/pH stress. Bivalves may also induce intracellular stress to handle constant exposure to intracellular pathogens, requiring chaperone and HSPs to prevent apoptosis and retain cellular function ( Venier et al 2011 ; Gust et al 2013 ; Leite et al 2013 ; Al-Khalaifah and Afaf 2018 ; Smits et al 2020 ). In bivalves, members of this gene family are distributed throughout the genome (e.g., in Crassostrea gigas , they are present on six of the ten chromosomes; supplementary fig.…”

“…Hypoxic stress is inextricable from bivalve life history in the intertidal environment where access to oxygenated water is dependent on tide. It is also a secondary effect of the primary defence mechanism of shell clamping ( Long et al 2008 ) and is induced by bivalves during infection ( Al-Khalaifah and Afaf 2018 ; Smits et al 2020 ; Steffen et al 2020 ). OG53, the second most significantly bivalve-enriched gene family, consists of oxidoreductase and tyrosinase proteins ( P = 7.87×10 −6 , table 2 ).…”

Evolution of immune defence responses as incremental layers among Metazoa

“…Clonal expansion of selected hemocytes populations? ), the extreme diversification found in Biomphalaria glabrata FREPs allows the organism to combat the 200 million-year long parasitic relationship with digenean trematods (Al-Khalaifah & Al-Nasser 2019). FREPs are IgDP with a molecular machinery comparable to that present in arthropods for Dscam (see section 1.2), and thus display a high degree of sequence polymorphism through recombination and point mutations (Adema 2015).…”

Implication of the Type IV Secretion System in the Pathogenicity of Vibrio tapetis, the Etiological Agent of Brown Ring Disease Affecting the Manila Clam Ruditapes philippinarum

“…Hemocytes, which are the clam’s immune system cells, are recruited to the site of infection within the extrapallial fluids to eliminate the pathogen ( Allam et al., 2000 ). During a typical infection, hemocytes phagocytize foreign bacteria and mobilize the lysosome to eliminate them ( Al-Khalaifah and Al-Nasser, 2018 ). These immune cells are characterized by pseudopods, which are actin-rich membrane expansions, that make them able to catch and internalize bacteria.…”

“…These immune cells are characterized by pseudopods, which are actin-rich membrane expansions, that make them able to catch and internalize bacteria. During the development of BRD, V. tapetis cells are phagocytized by hemocytes, but once internalized, they inhibit several cellular functions such as actin polymerization or phagosome–lysosome fusion, thereby avoiding degradation ( Choquet et al., 2003 ; Paillard, 2004a ; Al-Khalaifah and Al-Nasser, 2018 ; Rahmani et al., 2019 ). Moreover, Reactive Oxygen Species (ROS) production is reduced in infected hemocytes ( Paillard, 2017 ).…”