The inflammatory Response of Urochordata : The basic process of the Ascidians' innate immunity

Abstract

Ascidians form a widespread marine invertebrate group and are heterogeneous in terms of the taxonomic groups’ evolutionary lineages. The ascidian genomes lack significant homologies for rearranging genes of the vertebrate adoptive immunity. Genome analysis, gene sequencing, and transcriptional profiling have allowed us to disclose upregulation of innate immunity genes and cell labeling with riboprobes and antibodies has identified hemocyte types in tunic and pharynx inflammatory responses. Lymphocyte-like cells are stem cells and their immunocompetence has been proposed. Granulocyte types (compartment/morula cells) and hemocytes with large granules/vacuoles (compartment/morula cells) are mature cells expressing and releasing inflammatory components. LPS stimulates gene families of innate immune receptor homologs of the mammalian counterparts, as well as immune regulatory genes, during inflammatory responses. Proinflammatory components are involved in allogeneic reactions, and nonself and missing-self recognitions may be proposed. The findings on Ig-like domains contained in chitin-binding proteins (VCBPs) indicate the ancestral origin of vertebrate adaptive immunity and show that relevant genetic circuitry was already in place in the common ancestor of the protochordates and vertebrates. On the other hand, ascidians share with the other invertebrates the prophenoloxidase system that produces melanin and is involved in the inflammatory cytotoxic mechanism. The peroxinectin gene is also upregulated. Damage signals could be proinflammatory, but there are difficulties in assessing this that presumably could be examined during larva metamorphosis. Findings indicate that genetic circuitries relevant for vertebrate innate immunity were already in place in the common ancestor of the protochordates and vertebrates.