B cell Rab7 mediates induction of activation-induced cytidine deaminase expression and class-switching in T-dependent and T-independent antibody responses

J Immunol. 2015 Apr 1;194(7):3065-78. doi: 10.4049/jimmunol.1401896. Epub 2015 Mar 4.

Abstract

Class switch DNA recombination (CSR) is central to the maturation of the Ab response because it diversifies Ab effector functions. Like somatic hypermutation, CSR requires activation-induced cytidine deaminase (AID), whose expression is restricted to B cells, as induced by CD40 engagement or dual TLR-BCR engagement (primary CSR-inducing stimuli). By constructing conditional knockout Igh(+/C)γ(1-cre)Rab7(fl/fl) mice, we identified a B cell-intrinsic role for Rab7, a small GTPase involved in intracellular membrane functions, in mediating AID induction and CSR. Igh(+/C)γ(1-cre)Rab7(fl/fl) mice displayed normal B and T cell development and were deficient in Rab7 only in B cells undergoing Igh(C)γ(1-cre) Iγ1-Sγ1-Cγ1-cre transcription, as induced--like Igh germline Iγ1-Sγ1-Cγ1 and Iε-Sε-Cε transcription--by IL-4 in conjunction with a primary CSR-inducing stimulus. These mice could not mount T-independent or T-dependent class-switched IgG1 or IgE responses while maintaining normal IgM levels. Igh(+/C)γ(1-cre)Rab7(fl/fl) B cells showed, in vivo and in vitro, normal proliferation and survival, normal Blimp-1 expression and plasma cell differentiation, as well as intact activation of the noncanonical NF-κB, p38 kinase, and ERK1/2 kinase pathways. They, however, were defective in AID expression and CSR in vivo and in vitro, as induced by CD40 engagement or dual TLR1/2-, TLR4-, TLR7-, or TLR9-BCR engagement. In Igh(+/C)γ(1-cre)Rab7(fl/fl) B cells, CSR was rescued by enforced AID expression. These findings, together with our demonstration that Rab7-mediated canonical NF-κB activation, as critical to AID induction, outline a novel role of Rab7 in signaling pathways that lead to AID expression and CSR, likely by promoting assembly of signaling complexes along intracellular membranes.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antibody Formation*
  • Antibody Specificity / immunology
  • Antigens / immunology
  • B-Lymphocytes / cytology
  • B-Lymphocytes / immunology*
  • B-Lymphocytes / metabolism*
  • Cell Differentiation / genetics
  • Cell Differentiation / immunology
  • Cell Survival / drug effects
  • Cell Survival / immunology
  • Cytidine Deaminase / genetics*
  • Gene Expression Regulation*
  • Gene Order
  • Genetic Loci
  • Germ Cells / metabolism
  • Immunoglobulin Class Switching*
  • Immunoglobulin E / biosynthesis
  • Immunoglobulin E / genetics
  • Immunoglobulin E / immunology
  • Immunoglobulin G / biosynthesis
  • Immunoglobulin G / genetics
  • Immunoglobulin G / immunology
  • Immunoglobulin Heavy Chains / genetics
  • Immunoglobulin gamma-Chains / genetics
  • Interleukin-4 / metabolism
  • Lymphocyte Activation / immunology
  • Mice
  • Mice, Transgenic
  • NF-kappa B / metabolism
  • T-Lymphocytes / cytology
  • T-Lymphocytes / immunology*
  • T-Lymphocytes / metabolism
  • Transcription, Genetic
  • rab GTP-Binding Proteins / deficiency
  • rab GTP-Binding Proteins / genetics
  • rab GTP-Binding Proteins / metabolism*
  • rab7 GTP-Binding Proteins

Substances

  • Antigens
  • Immunoglobulin G
  • Immunoglobulin Heavy Chains
  • Immunoglobulin gamma-Chains
  • NF-kappa B
  • rab7 GTP-Binding Proteins
  • rab7 GTP-binding proteins, human
  • rab7 GTP-binding proteins, mouse
  • Interleukin-4
  • Immunoglobulin E
  • AICDA (activation-induced cytidine deaminase)
  • Cytidine Deaminase
  • rab GTP-Binding Proteins