Echinoderm Antimicrobial Peptides: The Ancient Arms of the Deuterostome Innate Immune System

Antimicrobial peptides (AMPs) are widely expressed in organisms and have been linked to innate and acquired immunity in vertebrates. These compounds are constitutively expressed from different cellular types to interact directly with infectious agents and/or modulate immunoreactions. In invertebrates, including echinoderms, which lack a vertebrate-type adaptive immune system, AMPs represent the major humoral defense system against infection, showing a diverse spectrum of action mechanisms, most of them related to plasma membrane disturbance and lethal alteration of microbial integrity. Here, we summarize the knowledge of AMPs in echinoderms as Strongylocins identified in the sea urchins, Strongylocentrotus droebachiensis and Strongylocentrotus purpuratus, focusing attention on peptides that exhibit an antibiofilm activity, as Paracentrin 1 from Paracentrotus lividus and Holoturoidin 1 and 2 from sea cucumber Holothuria tubulosa. Future studies on AMPs should be aimed at revealing how echinoderms use these AMPs in the immune response against microbial pathogens.