Reactive oxygen species released from granulocytes stimulate 5-lipoxygenase activity in a B-lymphocytic cell line

B-lymphocytes express 5-lipoxygenase (5-LO) protein but cellular leukotrien e production is suppressed by selenium-dependent peroxidases. Thus it was o f interest to check whether reactive oxygen species (ROS) which are release d under inflammatory conditions can stimulate B-lymphocyte 5-LO and counter act peroxidase-mediated suppression of cellular 5-LO activity. It was found that 5-LO in the Epstein-Barr virus-transformed B-lymphocytic cell line BL 41-E95-A is activated by addition of hydrogen peroxide or xanthine/xanthine oxidase and after increasing the oxidative state of the cell by azodicarbo xylic acid bis(dimethylamide). Generation of endogenous ROS from mitochondr ia by antimycin A also lead to a threefold upregulation of 5-LO activity in B-cells. There was almost no detectable endogenous superoxide formation in BL41-E95- A cells after stimulation with 4 beta-phorbol 12-myristate 13-acetate. Co-i ncubation experiments with BL41-E95-A cells and granulocytes demonstrated t hat granulocyte-derived ROS can activate B-lymphocyte 5-LO. Addition of sup eroxide dismutase and/or catalase to the B-lymphocyte/granulocyte co-incuba tions and to B-lymphocyte homogenates revealed that the 5-LO activation is due to the superoxide-derived release of hydroperoxides or hydrogen peroxid e from granulocytes. The data suggest that ROS formation plays an important role in the regulati on of cellular 5-LO activity in B-lymphocytes. As leukotrienes affect B-cel l functions like cell proliferation, activation and maturation, this findin g provides a new link between the formation of ROS and the regulation of im mune responses.