The echinoderm innate humoral immune response

Abstract

Multicellular organisms have an immune system, which is essential for the survival of living beings. Interest in the immune system has been expanded since common characteristics of innate immunity between Drosophila melanogaster (Meigen, 1830) and mammals were discovered in the 1980. Since then, immunology has mainly focused on the adaptive immune system that seems to be restricted to vertebrates. Unlike the innate immunity, the adaptive one is acquired after exposure to a specific antigen (Ag) and includes: antigen-presenting cells such as macrophages, proliferation of B and T lymphocytes, Ag-specific antibody/cytokine production and immunological memory. Innate immunity is instead a process of cellular defense at low specificity, which is designed to prevent and combat infectious agents that penetrate at the tissue level, and may be the only form of immunity present in invertebrates such as sea urchins. The immune system of invertebrates acts through (i) cellular components (cell-mediated immunity) in which the effectors of defense reactions are represented by immune cells; (ii) soluble factors (humoral immunity), secreted by the immune cells, such as lectins, agglutinins, lysins, antimicrobial peptides and the prophenoloxidase (proPO) activating system, which act in parallel with the immune cells to fight pathogens and other foreign substances. Here we aim to deepen the study on humoral immunity of invertebrates, especially referring to the phylum Echinodermata because of its features shared with protostomes and other deuterostomes, and suggesting a key step during evolution.

Evolutionary conserved pathway of the innate immune response after a viral insult in Paracentrotus lividus sea urchin

“…They possess an innate immune system that acts through humoral and cellular responses. The cellular response is mediated by a particular class of cells, the immune cells, that circulate in the coelomic cavity and can infiltrate tissues and organs; they act through different activating pathways in response to host invasion, insult and cytotoxic agents (Chiaramonte & Russo, ; Pinsino & Matranga, ; Smith et al., ). Since the appearance of the first eukaryotic cells on Earth, many defence mechanisms have evolved to ensure cell integrity, homeostasis and organ survival.…”

“…Many echinoderms have been used as model systems for studies on immunology as well as cell and developmental biology (Chiaramonte & Russo, ; Smith et al., ).…”

The role of fasting on spine regeneration and bacteremia in the purple sea urchin Strongylocentrotus purpuratus

“…Matranga et al [19] found elevated red spherula counts in Paracentrotus lividus urchins with spineless lesions covering 10 to 20% of the body whereas mechanical damage is known to increase ceolomocyte number and humoral molecule expression [20]. While many studies have investigated the immune response in sea urchins [21][22][23], few have considered the impact of spine damage on immune function and bacteremia.…”

Development and morphology of ciliary urns in the sea cucumber Synaptula hydriformis (Echinodermata: Holothuroidea)

“…The echinoderm immune system consists of cellular and humoral components (Chiaramonte & Russo, ; Ramírez‐Gómez & García‐Arrarás, ; Smith & Davidson, ; Smith et al, ). Cellular defense comprises various types of coelomocyte with humoral defenses mediated by numerous immune‐specific molecules (Chiaramonte & Russo, ; Ramírez‐Gómez & García‐Arrarás, ; Smith et al, ). The axial organ of the coelom is the only organ currently believed to play a role in immune response in echinoderms (Millott, ), possibly through coelomocyte production (Endean, ; Ramírez‐Gómez & García‐Arrarás, ).…”

“…As deuterostomes, echinoderms are close relatives of vertebrates. Because of their close phylogenetic association, greater knowledge of the immune systems of echinoderms might help elucidate the evolution and nature of vertebrate immune systems (Chiaramonte & Russo, ; Ramírez‐Gómez & García‐Arrarás, ; Smith & Davidson, ).…”