Immunity in Molluscs: Recognition and Effector Mechanisms, with a Focus on Bivalvia

Abstract

The study of molluscan immune systems, and in particular those of bivalve molluscs (clams, oysters, scallops, mussels, etc.) has experienced great growth in recent decades, mainly due to the needs of a rapidly growing aquaculture industry to manage the impacts of disease and the application of -omic tools to this diverse group of invertebrate organisms. Several unique aspects of molluscan immune systems highlighted in this chapter include the importance of feeding behavior and mucosal immunity, the discovery of unique levels of diversity in immune genes, and experimental indication of transgenerational immune priming. The development of comparative functional studies using natural and selectively bred disease-resistant strains, together with the potential but yet to be fully developed application of gene-editing technologies, should provide exciting insights into the functional relevance of immune gene family expansion and molecular diversification in bivalves. Other areas of bivalve immunity that deserve further study include elucidation of the process of hematopoiesis, the molecular characterization of hemocyte subpopulations, and the genetic and molecular mechanisms underlying immune priming. While the most important aspects of the immune system of the largest group of molluscs, gastropods (e.g., snails and slugs), are discussed in detail in Chap. 12, we also briefly outline the most distinctive features of the immune system of another fascinating group of marine molluscs, cephalopods, which include invertebrate animals with extraordinary morphological and behavioral complexity.

Shift in Immune Parameters After Repeated Exposure to Nanoplastics in the Marine Bivalve Mytilus

“…Bivalves express a wide range of inducible immune-related genes codifying for extracellular recognition and effector proteins, including lectins, peptidoglycan recognition proteins, lipopolysaccharide and β1,3-glucan-binding proteins, FREPs, and AMPs (58). The sequencing of the Mytilus genome reveals a very complex organization with high heterozygosity, abundant repetitive sequences, and extreme intraspecific sequence diversity among individuals (58)(59)(60)(61). This complex machinery would be responsible for the high capacity of mussels to cope with microbial infection and environmental stress.…”

Cephalopod Tissue Regeneration: Consolidating Over a Century of Knowledge

“…Among these, one of the most important has been establishment of the role of hemocytes, the circulating cellular components that form the basis of the cephalopod immune system (for review see Gerdol et al, 2018 ), in various phases of the regeneration process (Lange, 1920 ; Sereni and Young, 1932 ; Féral, 1978 , 1979 , 1988 ; Polglase et al, 1983 ; Imperadore et al, 2017 ). Almost all studies of regeneration in cephalopods report the involvement of hemocytes which rush to the site of the lesion to form a scar, and although this tissue forms a protective plug against pathogens, it does not present a physical barrier to regenerative phenomena (Lange, 1920 ; Polglase et al, 1983 ; Féral, 1988 ).…”

Phylogenetic analysis of the caspase family in bivalves: implications for programmed cell death, immune response and development

“…The implications of programmed cell death and additional in ammation responses have also been widely discussed in relation to the bivalve innate immune system (1,2,4,6,(78)(79)(80). Haemocytes are one of the crucial executioners of invertebrate immune responses, and one of the proposed key strategies of haemocytes is to undergo apoptosis when infected by a pathogen, or when they have ingested invaders through phagocytosis to prevent proliferation and spread.…”

“…The innate immune system of bivalves, including cellular and humoral responses, is one of the most important and sophisticated defence mechanisms among invertebrates. It utilises strategies such as phagocytosis, encapsulation, autophagy and humoral effectors for pathogen recognition and elimination (1,2). One of these strategies also includes apoptosis, a type of programmed cell death, to prevent the spread of pathogens.…”