Circulating hemocytes and pharyngeal explants of Styela clava release hemagglutinin in vitro

Tunicate blood cells are a mixed population, thus experiments that assay their immunodefense responses, such as release of hemagglutinins, were done to isolate different functional hemocytic types. Two sources of hemocytes from Styela clava were used, the hemolymph and the pharynx (the hemopoietic organ). Hemolymph centrifuged through a discontinuous Percoll gradient yielded four distinct bands of hemocytes. After incubation at 15°C, circulating hemocytes and those from pharyngeal cultures released hemagglutinin after 2 and 30 days. Highest titers were found in B1 (hyaline and compartment cells), B3 (hyaline cells and eosinophil granulocytes), and B4 (hyaline cells and debris). Hemagglutinating activity was also found after homogenization of the hemocyte bands except for B2. Homogenate of fresh pharyngeal explants showed no hemagglutinating activity but tissues cultured for 30 days had titers up to 1:16. These results are unique in pointing out the capacities of two tunicate hemocyte types (circulating, pharyngeal) to: release hemagglutinin in vitro and assign at least one functional property to discrete populations.