Stimulation of starfish coelomocytes by interleukin-1

Echinoderms have coelomocytes that are capable of non-specific phagocytosis of pathogens and cellular debris. It has been suggested that cytokines, analogous to vertebrate interleukins, are involved in mediating these responses, though how they may function is not known. Using a mouse thymocyte proliferation assay we confirm that cytokine activity, which can be blocked with antibodies to mammalian IL-1 alpha, can be extracted from coelomic fluid of the starfish Pisaster ochraceus. A subset of starfish coelomocytes in primary culture will readily phagocytose bacteria added to cultures. In a microscopic assay the proportion of coelomocytes that will phagocytose bacteria increases significantly when cultures are treated with recombinant IL-1 alpha, yet the number of phagosomes per cell remains constant. We propose that endogenous interleukins stimulate recruitment of phagocytic cells as part of the non-specific cellular defence mechanism of asteroids.