Phosphoinositide 3-Kinase p110δ Regulates Natural Antibody Production, Marginal Zone and B-1 B Cell Function, and Autoantibody Responses

B-1 and marginal zone (MZ) B cells produce natural Abs, make Ab responses to microbial pathogens, and contribute to autoimmunity. Although the delta isoform of the PI3K p110 catalytic subunit is essential for development of these innate-like B cells, its role in the localization, activation, and function of normal B-1 and MZ B cells is not known. Using IC87114, a highly selective inhibitor of p110 delta enzymatic activity, we show that p110 delta is important for murine B-1 and MZ B cells to respond to BCR clustering, the TLR ligands LPS and CpG DNA, and the chemoattractants CXCL13 and sphingosine 1-phosphate. In these innate-like B cells, p110 delta activity mediates BCR-, TLR- and chemoattractant-induced activation of the Akt prosurvival kinase, chemoattractant-induced migration, and TLR-induced proliferation. Moreover, we found that TLR-stimulated Ab responses by B-1 and MZ B cells, as well as the localization of MZ B cells in the spleen, depend on p110 delta activity. Finally, we show that the in vivo production of natural Abs requires p110 delta and that p110 delta inhibitors can reduce in vivo autoantibody responses. Thus, targeting p110 delta may be a novel approach for regulating innate-like B cells and for treating Ab-mediated autoimmune diseases. The Journal of Immunology, 2009, 183: 5673-5684.