Platyhelminthes: Molecular Dissection of the Planarian Innate Immune System
Multicellular organisms rely on their immune system to fight pathogens, maintain homeostasis, and repair tissues. Different environments and evolutionary paths have contributed to a myriad of strategies by which animals activate their immune system in response to body demands. Thus, invertebrate organisms lacking an adaptive immunity eliminate pathogenic microbes and heal tissues from injuries by activating the innate immune system. Planarians are invertebrates, members of the phylum Platyhelminthes (flatworms) and a classical model for studies of tissue regeneration. Recent work in planarians revealed an astonishing capacity to effectively recognize and eliminate a wide spectrum of pathogenic bacteria. Furthermore, planarians and humans display evolutionary conservation of signaling pathways and components associated with the microbiome that together contribute to the innate immune system. Organismal changes in the composition of commensal bacteria have important effects in tissue maintenance and repair of planarian tissues. Here, we focus on the planarian model system as a tractable paradigm to identify evolutionarily conserved mechanisms of innate immunity that can be further exploited in clinical settings to induce rapid clearance of pathogenic bacteria and modulation of regenerative events. We also propose the use of planarians as a reference organism for studies of comparative immunology.
KeywordsInnate immunity Regeneration Planarians Platyhelmithes Invertebrates Microbiome Bacterial clearance Phagocytosis Neoblasts Stem cells
We thank Devon Davidian for assistance with illustrations and members of the Oviedo Lab for comments on the manuscript.
The authors declare no competing or financial interests.
We acknowledge support from the National Science Foundation graduate fellowship award 1744620 to EIM, and the University of California Cancer Research Coordinating Committee (Award# CRR-18-525108) and National Cancer Institute and National Institute of General Medical Sciences of the National Institute of Health awards CA176114 and GM109372 to NJO.
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