Search

Previous studies have identified proteins from tunicates (invertebrate members of the Phylum Chordata) that have physicochemical and functional properties similar to those of the inflammatory cytokine, interleukin 1 (IL-1). Here we characterize one of those proteins from the tunicate, Styela plicata, that can stimulate tunicate and mammalian cell proliferation, activate phagocytosis, increase interleukin 2 (IL-2) secretion by mammalian peripheral blood mononuclear cells and enhance IL-2 receptor (IL-2R) expression by mammalian EL-4.IL-2 cells. Partial amino acid sequence data showed that the S. plicata protein resembles three C-type lectins (TC14, TC14-1 and TC14-2) from a closely related tunicate species, Polyandrocarpa misakiensis. Its similarity to carbohydrate recognition domains (CRDs) from P. misakiensis lectins suggests that the S. plicata protein modulates the activities of mammalian immunocompetent cells by interacting with carbohydrate moieties of glycosylated cell surface receptors.

Tunicates are filter feeding marine invertebrates that are susceptible to environmental contamination by toxic metals and polyaromatic hydrocarbons. Recently, we have shown that tunicate immune reactions are profoundly affected by exposure to tributyltin (TBT) and copper, both of which are components of marine antifouling paints. This study tests the effects of those pollutants on the hemocytes of tunicates. Immunofluorescence labeling with an anti-hemocyte monoclonal antibody demonstrated that the antigenic structure of the circulating hemocyte population was substantially affected by TBT and copper. Antigen-positive hemocytes were also found to accumulate in the pharyngeal papillae of TBT-exposed tunicates. Histological analyses indicated that this cellular accumulation in pharyngeal papillae involved refractile vacuolated hemocytes. Refractile vacuolated cells from TBT-exposed tunicates also occurred at greater frequencies in the circulating hemolymph, and had altered morphologies, compared to cells from nontreated controls. These data confirm that exogenous metals can have profound effects on the hemocytes of tunicates.

Hemocytes from the tunicate, Styela plicata, undertake cytotoxic responses toward human KS62 tumor cells or rabbit red blood cells (RRBC). Reactions to both target cell types were found to require metabolic activity. However, it was not determined whether killing involves soluble factors or direct cell/cell contact. Differences in the response to varied effector: target ratios indicate that reactions against the K562 cells and RRBC are mediated by separate mechanisms. The existence of two discrete cytotoxic mechanisms was supported by experiments which demonstrated that pharmacological treatments have different effects on the cytotoxic destruction of K562 cells and RRBC. Moreover, cytotoxic reactions toward the different targets cells were shown to be mediated by different hemocyte sub-populations isolated from hemolymph by density gradient centrifugation.