4-hydroxy-5-nitrophenyl-acetic-acid and Streptococcal-Infections

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.

Topics: Animals; Antibodies, Bacterial; Antibody Affinity; Antibody Diversity; Antibody Formation; B-Lymphocytes; Bacterial Capsules; Cell Lineage; Cytidine Deaminase; Enzyme Activation; Gene Knock-In Techniques; Germinal Center; Haptens; Housing, Animal; Immunization; Immunoglobulin Class Switching; Immunoglobulin G; Mice; Mice, Knockout; Nitrophenols; Phenylacetates; Signal Transduction; Somatic Hypermutation, Immunoglobulin; Spleen; Streptococcal Infections; Streptococcus pneumoniae; TOR Serine-Threonine Kinases