Frontiers in Immunology (Jun 2022)

Cellular Mechanisms Underlying B Cell Abnormalities in Patients With Gain-of-Function Mutations in the PIK3CD Gene

  • Wenjie Wang,
  • Qing Min,
  • Nannan Lai,
  • Krisztian Csomos,
  • Ying Wang,
  • Luyao Liu,
  • Xin Meng,
  • Jinqiao Sun,
  • Jia Hou,
  • Wenjing Ying,
  • Qinhua Zhou,
  • Bijun Sun,
  • Xiaoying Hui,
  • Boglarka Ujhazi,
  • Sumai Gordon,
  • David Buchbinder,
  • Catharina Schuetz,
  • Manish Butte,
  • Jolan E. Walter,
  • Jolan E. Walter,
  • Xiaochuan Wang,
  • Xiaochuan Wang,
  • Ji-Yang Wang,
  • Ji-Yang Wang,
  • Ji-Yang Wang,
  • Ji-Yang Wang

DOI
https://doi.org/10.3389/fimmu.2022.890073
Journal volume & issue
Vol. 13

Abstract

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BackgroundActivated phosphoinositide 3 kinase (PI3K) -delta syndrome (APDS) is an inborn error of immunity with variable clinical phenotype of immunodeficiency and immune dysregulation and caused by gain-of-function mutations in PIK3CD. The hallmark of immune phenotype is increased proportions of transitional B cells and plasmablasts (PB), progressive B cell loss, and elevated levels of serum IgM.ObjectiveTo explore unique B cell subsets and the pathomechanisms driving B cell dysregulation beyond the transitional B cell stage in APDS.MethodsClinical and immunological data was collected from 24 patients with APDS. In five cases, we performed an in-depth analysis of B cell phenotypes and cultured purified naïve B cells to evaluate their survival, activation, Ig gene class switch recombination (CSR), PB differentiation and antibody secretion. We also analyzed PB differentiation capacity of sorted CD27-IgD- double-negative B (DNB) cells.ResultsThe patients had increased B cell sizes and higher proportions of IgM+ DNB cells than healthy controls (HC). Their naïve B cells exhibited increased death, impaired CSR but relatively normal PB differentiation. Upon stimulation, patient’s DNB cells secreted a similar level of IgG but a higher level of IgM than DNB cells from HC. Targeted therapy of PI3K inhibition partially restored B cell phenotypes.ConclusionsThe present study suggests additional mechanistic insight into B cell pathology of APDS: (1) decreased peripheral B cell numbers may be due to the increased death of naïve B cells; (2) larger B cell sizes and expanded DNB population suggest enhanced activation and differentiation of naïve B cells into DNB cells; (3) the impaired CSR yet normal PB differentiation can predominantly generate IgM-secreting cells, resulting in elevated IgM levels.

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