title: B cell-specific deficiencies in mTOR limit humoral immune responses.
abstract: Generation of high-affinity Abs in response to Ags/infectious agents is essential for developing long-lasting immune responses. B cell maturation and Ab responses to Ag stimulation require Ig somatic hypermutation (SHM) and class-switch recombination (CSR) for high-affinity responses. Upon immunization with either the model Ag 4-hydroxy-3-nitrophenylacetyl hapten (NP) conjugated to chicken γ globulin lysine (NP-CGG) or heat-killed Streptococcus pneumoniae capsular type 14 protein (Pn14), knock-in (KI) mice hypomorphic for mTOR function had a decreased ability to form germinal centers, develop high-affinity anti-NP-specific or anti-Pn14-specific Abs, and perform SHM/CSR. Hypomorphic mTOR mice also had a high mortality (40%) compared with wild-type (WT) (0%) littermates and had lower pneumococcal surface protein A-specific Ab titers when immunized and challenged with live S. pneumoniae infection. Mice with mTOR deleted in their B cell lineage (knockout [KO]) also produced fewer splenic germinal centers and decreased high-affinity Ab responses to NP-CGG than did their WT littermates. CSR rates were lower in mTOR KI and KO mice, and pharmacologic inhibition of mTOR in WT B cells resulted in decreased rates of ex vivo CSR. RNA and protein levels of activation-induced cytidine deaminase (AID), a protein essential for SHM and CSR, were lower in B cells from both KI and B cell-specific KO mice, concomitant with increases in phosphorylated AKT and FOXO1. Rescue experiments increasing AID expression in KI B cells restored CSR levels to those in WT B cells. Thus, mTOR plays an important immunoregulatory role in the germinal center, at least partially through AID signaling, in generating high-affinity Abs.
authors.affiliation: Laboratory of Cancer Biology and Genetics, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Shuling
authors.initials: S
authors.lastname: Zhang
authors.forename: Margaret
authors.initials: M
authors.lastname: Pruitt
authors.forename: Dena
authors.initials: D
authors.lastname: Tran
authors.forename: Wendy
authors.initials: W
authors.lastname: Du Bois
authors.forename: Ke
authors.initials: K
authors.lastname: Zhang
authors.forename: Rushi
authors.initials: R
authors.lastname: Patel
authors.forename: Shelley
authors.initials: S
authors.lastname: Hoover
authors.forename: R Mark
authors.initials: RM
authors.lastname: Simpson
authors.forename: John
authors.initials: J
authors.lastname: Simmons
authors.forename: Joy
authors.initials: J
authors.lastname: Gary
authors.forename: Clifford M
authors.initials: CM
authors.lastname: Snapper
authors.forename: Rafael
authors.initials: R
authors.lastname: Casellas
authors.forename: Beverly A
authors.initials: BA
authors.lastname: Mock
mesh_terms: D000818:Animals; D000907:Antibodies, Bacterial / Q000096:biosynthesis / Q000276:immunology; D000915:Antibody Affinity; D000916:Antibody Diversity; D000917:Antibody Formation; D001402:B-Lymphocytes / Q000276:immunology*; D016667:Bacterial Capsules / Q000276:immunology; D019070:Cell Lineage; D003564:Cytidine Deaminase / Q000276:immunology*; D004789:Enzyme Activation; D055879:Gene Knock-In Techniques; D018858:Germinal Center / Q000276:immunology / Q000473:pathology; D006241:Haptens / Q000276:immunology; D006799:Housing, Animal; D007114:Immunization; D017578:Immunoglobulin Class Switching; D007074:Immunoglobulin G / Q000276:immunology; D051379:Mice; D018345:Mice, Knockout; D009596:Nitrophenols / Q000276:immunology; D010648:Phenylacetates / Q000276:immunology; D015398:Signal Transduction / Q000276:immunology; D027041:Somatic Hypermutation, Immunoglobulin; D013154:Spleen / Q000276:immunology / Q000473:pathology; D013290:Streptococcal Infections / Q000276:immunology; D013296:Streptococcus pneumoniae / Q000276:immunology; D058570:TOR Serine-Threonine Kinases / Q000276:immunology*; D000098830:AICDA (Activation-Induced Cytidine Deaminase)
chemical_list: D000907:Antibodies, Bacterial; D006241:Haptens; D007074:Immunoglobulin G; D009596:Nitrophenols; D010648:Phenylacetates; C056696:pneumococcal polysaccharide, type 14; C026242:4-hydroxy-5-nitrophenyl acetic acid; C546843:mTOR protein, mouse; D058570:TOR Serine-Threonine Kinases; D000098830:AICDA (Activation-Induced Cytidine Deaminase); D003564:Cytidine Deaminase