increased after activation regardless of cMyc expression. The PI3K/ Akt pathway has been shown to promote glucose uptake and glycolysis in BCR-stimulated B cells. In IL-4 stimulated B cells, however, the PI3K/Akt pathway appeared dispensable, with STAT6 instead required. In LPS-stimulated PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19846036 B cells, it is likely that cMyc combined with the PI3K/Akt pathway reprogram glucose metabolism. In this setting, it may be that cMyc leads to induction of gene expression and the PI3K/Akt pathway plays a post-translational and coordinating role to orchestrate the metabolic transition from resting to activation. While these pathways may control glucose metabolic pathways, the regulation of mitochondrial pathways remains uncertain. We also show here that tolerance strongly influences B cell metabolism. Self-reactive B cells that become anergic were found metabolically suppressed to both BCR and TLR4 ligation. The completely inability of anergic B cells to metabolically reprogram in response to BCR stimulation was likely due in part to desensitized antigen receptor. In particular, failure to activate the PI3K/Akt signaling pathway may prevent upregulation of glycolytic metabolism. LPS was able to partially induce glycolysis and mitochondrial oxygen consumption of anergic B cells. Therefore, tolerance does not lead to wholesale inhibition of metabolic reprogramming. It remains unclear to what extent anergic B cells have intrinsic metabolic defects relative to desensitized antigen receptor or TLR signals that fail to properly upregulate metabolic regulatory pathways. In both settings, however, metabolic reprogramming is decoupled from receptor stimulation in anergic B cells. In contrast to B cell anergy, B cells chronically exposed to high levels of BAFF showed enhanced and more rapid metabolic reprogramming upon TLR4 ligation. In particular, aerobic glycolysis increased rapidly to transiently shift the balance of metabolism to predominantly glycolytic. Oxygen consumption also increased, albeit at a slower rate. The differential rates of glycolytic and mitochondrial metabolism in BAFF transgenic B cells may reflect altered activity of signaling pathways that control glycolysis relative to mitochondrial metabolism. Acute treatment with BAFF can activate the PI3K/Akt signaling pathway, but we found this insufficient to alter B cell metabolism on its own. It may be that chronic exposure to BAFF or additional signals are necessary. Thus, failure to properly induce tolerance due to chronically high levels of BAFF primes B 
cells to rapidly reprogram to the glycolytic metabolism, essential for activated antibody-producing cells. The broad upregulation of glycolytic and mitochondrial metabolism in B cell activation suggests that targeting these pathways may disrupt B cell antibody production. However, the balanced metabolism and use of multiple metabolic pathways may have allowed functional redundancy and provide B cells the ability to utilize a variety of metabolic fuels. We show here that 2-DG and DCA each suppress B cell proliferation and antibody production. 2-DG and DCA suppress the entire glucose metabolism pathway or direct pyruvate towards NIH-PA ONX-0914 Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript J Immunol. Author manuscript; available in PMC 2015 April 15. Caro-Maldonado et al. Page 11 mitochondrial oxidation, respectively. Although 2-DG can also induce cell death through ER stress, inhibiting PDHK did not affect B cell activation or surv
