STRUCTURE AND DIFFERENTIAL TARGET SENSITIVITY OF THE STIMULABLE CYTOTOXIC COMPLEX FROM HEMOLYMPH OF THE MEDITERRANEAN MUSSEL MYTILUS-GALLOPROVINCIALIS

A cytotoxic protein complex of 320 kDA was isolated from dialyzed plas ma of the edible mussel, Mytilus galloprovincialis. Constituted by the assembly of several different proteins, the complex exhibits selectiv e killing against eukaryotic cells, including erythrocytes, mouse tumo r cells and protozoan parasites. High variability, which was not corre lated with protein concentration, suggested that the immune response o f naive mussels was in various stages of activation. Stimulation assay s by different treatments in vivo resulted in significant increases in the activity of the plasma suggesting that cytotoxic complexes are in volved in immune defense. Lytic activity appears to involve binding of cytotoxic complexes onto target cell membranes and the formation of t ransmembrane pores. This research provides more evidence that the inna te immune system of invertebrates involves large cytotoxic proteins wi th a broad range of recognitive specificities in addition to small ant ibacterial, antifungal peptides.