A study of chemotaxis in the coelomocytes (blood cells) of Halocynthia roretzi

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The defense mechanism of ascidians is of special interest in the light of the evolutionary origin of the hauman immune system. In an aim to investigate this mechanism, we have transferred the coelomocytes of the solitary ascidian in culture and observed them with time-lapse videomocroscopy and scanning electron microscopy under various experimental conditions.The project was persued in four parts which will be described separately below.PRRT I : Classification of the coelomocytes in reference to those described in literature. Seven types, and one subtype, of cells were distinguished.PRRT II : Examination of phagocytotic activity of the coelomocyte types.Three types were found to phagocytose sheep red blood cells, while one type only bundled and held them to hand them over to other cell types.Four types were shown to incorporate carbon particles. Three of these, the same as above, excreted the particles quickly while one accumulated them in its cytoplasm.PRRT III : Indirect evidence showing participation of chemoattractant(s) in the defense action.Video-microscopic evidence shows that two types of cells are attacted to the site of a living invader. One of them is considered to emit a chemoattractant.PRRT IV : Agents inducing chemotaxis in the coelomocytes.Among thirteen kinds of solutions applied to the coelomocytes from the tip of a microneedle, seven induced chemotaxis. however, none of known chemoattractant of human immune system tested induced such behavior.