The functional activity of fractions of coelomocytes of the starfish <Emphasis Type="Italic">Asterias rubens</Emphasis> Linnaeus, 1758

As a result of the centrifugation of the circulating cells of the starfish Asterias rubens in a discontinuous density gradient of sodium diatrizoate, three cell fractions were separated. Small coelomocytes with a high nuclear–cytoplasmic ratio and the lack of granules prevailed in the upper fraction, coelomocytes with small granules evenly distributed in their cytoplasm dominated in the middle fraction, and large coelomocytes with a high content of large granules and vesicles in the perinuclear space were predominant in the bottom fraction. The coelomocytes of the separated fractions were tested for the production of reactive oxygen species, neutral red uptake, capture and internalization of the labeled bacteria Escherichia coli and Staphylococcus aureus, as well as for lytic activity and expression of the ArC3-like gene, which is a homologue of the C3 component of the mammalian complement cascade. Cells of the upper fraction manifested the most pronounced ability for the expression of the C3 gene homologue in response to stimulation with bacterial lipopolysaccharide. Coelomocytes of the middle fraction were distinguished by a pronounced ability to produce reactive oxygen species and phagocytosis, whereas the cells of the lower fraction had a high level of hemolytic activity and neutral red uptake.