It is well documented that reactive oxygen

intermediates (ROIs) are necessary for the innate immune system’s defense against microorganisms. Neutrophils and macrophages kill invading pathogens by activating the NADPH oxidase enzyme complex to produce superoxide (O2−), hydrogen peroxide (H2O2), and hydroxyl radicals (OH) [6, 7]. Recently, studies have begun to elucidate the role of ROIs in humoral immune responses. For instance, Capasso et al. [8] and Richards and Clark [9] demonstrated that murine B cells increase ROI levels following BCR ligation. These reports are consistent with an earlier study documenting that Autophagy Compound Library high throughput the A20 murine B-cell lymphoma line increased ROI levels upon anti-IgG stimulation [10]. Additionally, in vivo studies found that mice with B cells deficient in ROI

generating proteins have decreased antibody responses to T-cell dependent antigens, suggesting that ROIs act as positive regulators in B-cell responses [8]. However, Richards and Clark [9] determined that BCR-induced ROIs negatively regulated B-cell proliferation and antibody responses to T-cell-independent LY294002 molecular weight type 2 antigens. Together, these studies demonstrate that the role of ROIs in B-cell biology is complex and warrants further investigation. A particularly important unanswered question is the mechanisms by which ROIs affect B-cell activation. While ROIs can modify all macromolecules, reversible oxidation of cysteine is a mechanism to modulate signal transduction pathways. In the presence of ROIs, thiols (SH) can be oxidized to cysteine sulfenic acid (SOH) [11, 12]. This intermediate can be stabilized to a sulfenamide, form a disulfide bond with other protein thiols, undergo reduction, or be further oxidized to sulfinic (SO2H) or sulfonic (SO3H) acid [12]. These posttranslational modifications of cysteine act as a sensor for altering protein–protein interactions and function [13]. A recent study by Michalek et al. [14] documented that reversible cysteine sulfenic acid formation is necessary for naive CD8+ T-cell activation, proliferation, and

function. However, it was unknown whether this posttranslational HSP90 modification was necessary for B-cell activation. Here, we demonstrate that following antibody and antigen-mediated activation, B cells increase ROI levels. Using an antibody that recognizes proteins derivatized with 5,5-dimethyl-1,3-cyclohexanedione (dimedone), a compound that covalently reacts with cysteine sulfenic acid [15], we show that cysteine sulfenic acid levels increase following BCR ligation, and localize to both the cytoplasm and nucleus. We demonstrate that incubation of cells with dimedone resulted in a concentration-dependent block in anti-IgM induced proliferation. This decrease resulted from an inability of the cells in the presence of dimedone to sustain early tyrosine phosphorylation events and initiate capacitative calcium entry (CCE).