Genetic or pharmaceutical blockade of p110δ phosphoinositide 3-kinase enhances IgE production
Received 28 March 2008; received in revised form 2 July 2008; accepted 11 August 2008.
Background
Recent studies indicate that pharmaceutical blockade of phosphoinositide 3-kinase (PI3K) signaling enzymes might be effective in reducing allergic airway inflammation. Signals generated by the p110δ PI3K isoform play critical roles in signaling through antigen and cytokine receptors and were shown to be required for induction of type 2, but not type 1, cytokine responses.
Objective
We sought to determine the effect of genetic or pharmaceutical inactivation of p110δ PI3K on induction of IgE responses.
Methods
We determined the effect of p110δ inactivation on induction of systemic IgE responses and on the ability of purified B lymphocytes to undergo IgE isotype switch in vitro. IgG and IgE germline transcription, postswitch transcription, protein expression, and secretion were measured, as well as cell division and expression of activation-induced cytidine deaminase, an enzyme required for isotype switch.
Results
Paradoxically, inactivation of p110δ PI3K led to markedly increased IgE responses, despite reduced production of other antibody isotypes. This result was seen by using genetic inactivation of p110δ inhibition with IC87114 compound or blockade with the broad-spectrum PI3K inhibitors PIK-90 and PI-103. Significant increases in IgG1/IgE double-positive cells were observed, indicating that inactivation of PI3K leads to uncontrolled sequential switching from IgG1 to IgE. Disruption of p110δ signaling results in increased germline transcription at the ɛ locus and increased activation-induced cytidine deaminase expression, suggesting deregulation at the level of the isotype switch process.
Conclusion
Blockade of PI3K signaling leads to markedly enhanced B-cell switch to IgE and increased IgE levels in vivo, despite reduced type 2 cytokine production.
eHoward Hughes Medical Institute, Department of Cellular and Molecular Pharmacology, University of California, San Francisco, Calif
fInstitute of Cancer, Queen Mary's School of Medicine and Dentistry, University of London, London, United Kingdom
Reprint requests: Aaron J. Marshall, PhD, Department of Immunology, University of Manitoba, 730 William Ave, Winnipeg, MB, Canada.
Supported by the Canadian Institutes of Health Research (MOP-42382), the CIHR National Training Program in Allergy and Asthma Research, the SickKids Foundation (Toronto), and the Manitoba Institute of Child Health. T.Z. was supported by studentships from the Manitoba Institute of Child Health and the CIHR National Training Program in Allergy and Asthma Research. A.J.M. was supported by a Canada Research Chair.
Disclosure of potential conflict of interest: K. Okkenhaug has served as a consultant for Piramed and has received grants from the BBSRC and the British Heart Foundation. B. Vanhaesebroeck has served as a consultant for Piramed and AstraZeneca and has received research support from Piramed, UCB–CellTech and AstraZeneca. A. J. Marshall received operating grants from the Canadian Institutes of Health Research and the SickKids Foundation (Toronto). The rest of the authors have declared that they have no conflict of interest.
ABSTRACT