Ascidian cytotoxic cells: state of the art and research perspectives

Ascidian cytotoxic cells are multivacuolated cells, variable in morphology, abundantly represented in the circulation, playing important roles in ascidian immunosurveillance. Upon the recognition of foreign molecules, they are selectively recruited to the infection site where they release the content of their vacuoles. Their cytotoxic activity closely linked to the activity of the enzyme phenoloxidase (PO), a copper-containing enzyme widely distributed in invertebrates, contained inside their vacuoles together with its polyphenol substrata. Recent molecular data indicate that ascidian PO shares similarities with arthropod proPO but, unlike the latter, do not require enzymatic cleavage by extracellular serine proteinases for their activity. Possible ways of ascidian PO activation are discussed.