Proliferation of undifferentiated blood cells from the solitary ascidian, Ciona intestinalis in vitro.

ABSTRACT

The proliferative responses of the cytotoxic blood cell population of the solitary ascidian, Ciona intestinalis, were investigated by autoradiography and tritiated thymidine (3H-TdR) incorporation following treatment with mitogens or co-culture with allogeneic cells in vitro. A small number of mitotic figures were seen in untreated circulating blood cells and pulse labelling with 3H-TdR showed that only the undifferentiated "lymphocyte-like" cells within the enriched cytotoxic cell population undergo spontaneous cell division and DNA synthesis in the circulation. Treatment of the cells, cultured for 4 days, with concanavalin A (con A), phytohaemagglutinin-B (PHA-B) or lipopolysaccharide (LPS) produced significantly increased 3H-TdR incorporation, although there were differences in the sensitivity of the cells to mitogen concentration. Significantly enhanced proliferation was also observed following incubation with mitomycin C-treated cells from allogeneic individuals. These results show that the cytotoxic blood cell population of C. intestinalis is capable of mitogen-induced proliferation as well as mixed lymphocyte-type responses and therefore shares some proliferative characteristics with vertebrate lymphocytes.