Colony specificity and chemotaxis in the compound ascidian Botryllus schlosseri.

We re-investigated the behavior of hemocytes during the non-fusion (rejection) reaction between genetically incompatible colonies of the ascidian Botryllus schlosseri. In the course of the reaction, hemocytes - mainly morula cells - crowd inside the blind ends of marginal vascular vessels (known as ampullae) of the colonial leading edge (LE) facing the foreign colony which suggests the occurrence of chemotactic attraction of circulating hemocytes towards the ampullar lumen. Then, cells migrate, through the ampullar tips, into the partially fused tunics and contribute to the formation of the necrotic spots along the contact borders which characterize the reaction.

Cellular aspects of allorecognition in the compound ascidian Botryllus schlosseri.

We studied changes in the morphology of morula cells, a common haemocyte type in botryllid ascidians, during both the rejection reaction (occurring between contacting, genetically incompatible colonies) and fusion (occurring between compatible colonies), and in short-term cultures of haemocytes incubated with heterologous or autologous blood plasma. In both the rejection reaction and haemocyte cultures in the presence of heterologous blood plasma, we observed alterations in morula cells, consistent with a degranulation event, and their expression of molecules recognised by anti-IL-1-alpha- and anti-TNF-alpha-antibodies. Anti-cytokine-antibodies markedly reduced the extent of the in vitro cytotoxicity, when haemocytes were exposed to heterologous blood plasma.

Oxidative stress induces cytotoxicity during rejection reaction in the compound ascidian Botryllus schlosseri.

When genetically incompatible colonies of the compound ascidian Botryllus schlosseri contact each other, a rejection reaction occurs, characterised by the appearance of cytotoxic foci along the touching borders. In the course of this reaction, morula cells, a common haemocyte-type in ascidians, release their vacuolar content, mainly phenoloxidase and its polyphenol substrata, upon the recognition of soluble factors diffusing from the alien colony through the partially fused tunic. In a previous paper, we demonstrated the relationship between phenoloxidase and cytotoxicity.

Phagocyte spreading and phagocytosis in the compound ascidian Botryllus schlosseri: evidence for an integrin-like, RGD-dependent recognition mechanism.

The involvement of integrins in phagocyte spreading and phagocytosis was investigated in the compound ascidian Botryllus schlosseri. The number of spreading cells was significantly reduced when adhesion occurred in the presence of the tetrapeptide Arg--Gly--Asp--Ser (RGDS), but not of Arg--Gly--Glu--Ser (RGES) indicating the involvement of RGD-mediated adhesion mechanisms in phagocyte spreading. The significant decrease of the fraction of spreading cells in the presence of Botryllus blood plasma suggests the presence of RGD-containing molecules in the blood of our species.