Prolonged production of reactive oxygen species in response to B cell receptor stimulation promotes B cell activation and proliferation.

We have investigated the intracellular sources and physiological function of reactive oxygen species (ROS) produced in primary B cells in response to BCR stimulation. BCR stimulation of primary resting murine B cells induced the rapid production of ROS that occurred within minutes and was maintained for at least 24 h after receptor stimulation. While the early production of ROS (0-2 h) was dependent on the Nox2 isoform of NADPH oxidase, at later stages of B cell activation (6-24 h) ROS were generated by a second pathway, which appeared to be dependent on mitochondrial respiration. B cells from mice deficient in the Nox2 NADPH oxidase complex lacked detectable early production of extracellular and intracellular ROS after BCR stimulation but had normal proximal BCR signaling and BCR-induced activation and proliferation in vitro and mounted normal or somewhat elevated Ab responses in vivo. In contrast, neutralizing both pathways of BCR-derived ROS with the scavenger N-acetylcysteine resulted in impaired in vitro BCR-induced activation and proliferation and attenuated BCR signaling through the PI3K pathway at later times. These results indicate that the production of ROS downstream of the BCR is derived from at least two distinct cellular sources and plays a critical role at the later stages of B cell activation by promoting sustained BCR signaling via the PI3K pathway, which is needed for effective B cell responses to Ag.