Immunoregulatory potential of marine algal toxins yessotoxin and okadaic acid in mouse T lymphocyte cell line EL-4.

We have studied the effects of the marine algal toxins yessotoxin (YTX) and okadaic acid (OA) on the T cell receptor complex (TCR) expression, an important mechanism by which T cell responsiveness is controlled. Immune system cells are relevant targets to study the immunoregulatory potential of marine toxins since the immune system has been reported as one of the targets of marine algal toxins. This study reports results from exposing the mouse T lymphocyte cell line EL-4 to increasing concentrations of YTX and OA for 72h. We found that both YTX and OA affected TCR recycling kinetics and induced a specific and reversible TCR down-regulation in T lymphocyte EL-4 cells that was time and concentration dependent. Experiments using the potent protein kinase C (PKC) inhibitor stausporine indicated that YTX-induced TCR down-regulation was partially mediated by PKC activation. In contrast, OA-induced TCR down-regulation was mediated by the serine/threonine protein phophatase 2A (PP2A) inhibition. In summary, the results suggest that OA and YTX concentrations in a similar range than those detected in mice bloodstream after oral administration have the potential to adjust the T cell responsiveness during the initiation of T cell activation by affecting the TCR expression levels via PKC and PP2A activities.

New culture approaches for yessotoxin production from the dinoflagellate Protoceratium reticulatum.

Fed-batch and perfusion cultures were carried out in a traditional glass 2-L bioreactor with the toxic dinoflagellate Protoceratium reticulatum. The maximum cell concentration obtained was 2.3 x 105 cell.mL-1, which is almost 1 order of magnitude higher than the maximum previously referenced for this species. L1 medium was shown to be clearly deficient in nitrate and phosphate for this strain, and addition of highly concentrated aliquots of these nutrients allowed higher cell concentrations to be obtained. This species consumed high amounts of nitrate and phosphate, 2.1 x 10-3 and 2.3 x 10-4 micromol.h-1.cell-1, respectively. However, this consumption produced a very low number of cells compared to other classes of microalgae, indicating that this species is, like other dinoflagellates, a poor competitor in terms of utilization of inorganic nutrients. Higher production of toxins and pigments was strongly associated with cell number in the culture, with maximum values of 700 ng.mL-1 and 1321 microg.mL-1, respectively. Most yessotoxins remained within the cells and not in the cell-free culture medium, and their production was not related to either the age of the culture or the cell growth phase.