The production of amyloid requires cross-talk between immunocytes in the compound ascidian Botryllus schlosseri

Two main immunocyte types are present in the hemolymph of the compound ascidian Botryllus schlosseri, i.e. phagocytes and cytotoxic morula cells (MCs). Previous studies have demonstrated that MCs work as sentinel cells able to sense foreign molecules and, as a consequence, release cytokines which activate phagocytes leading to the synthesis and release of rhamnose-binding lectin. The latter, in turn, acts as a chemotactic factor for phagocytes and opsonizes foreign particles stimulating their clearance. In addition, upon the contact with foreign molecules, MCs can degranulate and release the content of their vacuoles, mainly phenoloxidase (PO) and its polyphenol substrata. In a recent investigation on Botryllus cytotoxic cells, we found abundance of amyloid inside MC vacuoles which likely, once released, act as a scaffold to prevent the diffusion of PO and cytotoxicity to the whole organism. In addition, the study of the molecular cascade leading to the synthesis of amyloid, is revealing a non-classical pathway in which both the phagocytes and MC are involved.