B cell Rab7 mediates induction of activation-induced cytidine deaminase expression and class-switching in T-dependent and T-independent antibody responses.
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.
Department of Microbiology and Immunology, School of Medicine, University of Texas Health Science Center, San Antonio, TX 78229;
Egest J
EJ
Pone
Department of Microbiology and Immunology, School of Medicine, University of Texas Health Science Center, San Antonio, TX 78229; Department of Molecular Biology and Biochemistry, University of California, Irvine, Irvine, CA 92697;
Tonika
T
Lam
Department of Microbiology and Immunology, School of Medicine, University of Texas Health Science Center, San Antonio, TX 78229;
Zheng
Z
Lou
Department of Microbiology and Immunology, School of Medicine, University of Texas Health Science Center, San Antonio, TX 78229; Xiangya Medical School, Central South University of China, 410000 Changsha, Hunan Province, China;
Rui
R
Wang
Center for Human Immunobiology, Texas Children's Hospital, Baylor College of Medicine, Houston, TX 77030; and.
Yuhui
Y
Chen
Center for Human Immunobiology, Texas Children's Hospital, Baylor College of Medicine, Houston, TX 77030; and.
Dongfang
D
Liu
Department of Developmental and Cell Biology, University of California, Irvine, Irvine, CA 92697.
Aimee L
AL
Edinger
Department of Microbiology and Immunology, School of Medicine, University of Texas Health Science Center, San Antonio, TX 78229; xuz3@uthscsa.edu pcasali@uthscsa.edu.
Zhenming
Z
Xu
Department of Microbiology and Immunology, School of Medicine, University of Texas Health Science Center, San Antonio, TX 78229; xuz3@uthscsa.edu pcasali@uthscsa.edu.
Paolo
P
Casali
D000818:Animals; D000917:Antibody Formation; D000918:Antibody Specificity / Q000276:immunology; D000941:Antigens / Q000276:immunology; D001402:B-Lymphocytes / Q000166:cytology / Q000276:immunology* / Q000378:metabolism*; D002454:Cell Differentiation / Q000235:genetics / Q000276:immunology; D002470:Cell Survival / Q000187:drug effects / Q000276:immunology; D003564:Cytidine Deaminase / Q000235:genetics*; D005786:Gene Expression Regulation; D023061:Gene Order; D056426:Genetic Loci; D005854:Germ Cells / Q000378:metabolism; D017578:Immunoglobulin Class Switching; D007073:Immunoglobulin E / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology; D007074:Immunoglobulin G / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology; D007143:Immunoglobulin Heavy Chains / Q000235:genetics; D007142:Immunoglobulin gamma-Chains / Q000235:genetics; D015847:Interleukin-4 / Q000378:metabolism; D008213:Lymphocyte Activation / Q000276:immunology; D051379:Mice; D008822:Mice, Transgenic; D016328:NF-kappa B / Q000378:metabolism; D013601:T-Lymphocytes / Q000166:cytology / Q000276:immunology* / Q000378:metabolism; D014158:Transcription, Genetic; D020691:rab GTP-Binding Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D000090802:rab7 GTP-Binding Proteins; D000098830:AICDA (Activation-Induced Cytidine Deaminase)
D000941:Antigens; D007074:Immunoglobulin G; D007143:Immunoglobulin Heavy Chains; D007142:Immunoglobulin gamma-Chains; D016328:NF-kappa B; D000090802:rab7 GTP-Binding Proteins; C000716463:rab7 GTP-binding proteins, human; C000716465:rab7 GTP-binding proteins, mouse; D015847:Interleukin-4; D007073:Immunoglobulin E; D000098830:AICDA (Activation-Induced Cytidine Deaminase); D003564:Cytidine Deaminase; D020691:rab GTP-Binding Proteins