Cell-dependent Antigen Research Articles

Reduced level of sialylated IgG antibody in the CSF of patients with multiple sclerosis

Background: A characteristic feature of the CNS inflammatory response in multiple sclerosis (MS) is the intrathecal synthesis of IgG and the presence of oligoclonal bands (OCBs). IgG form immune complexes with the antigen and generate negative feedback regulation through crosslinking the B cell receptor with the IgG inhibitory receptor FcγRIIB, which inhibits BCR signaling and thereby B cell activation and IgG Ab production. Recent studies showed that asialylated IgG antibody are proinflammatory and induced by the combination of T cell-dependent protein antigens and proinflammatory costimulation.

IKK-induced NF-κB1 p105 proteolysis is critical for B cell antibody responses to T cell-dependent antigen.

The importance of IκB kinase (IKK)-induced proteolysis of NF-κB1 p105 in B cells was investigated using Nfkb1(SSAA/SSAA) mice, in which this NF-κB signaling pathway is blocked. Nfkb1(SSAA) mutation had no effect on the development and homeostasis of follicular mature (FM) B cells. However, analysis of mixed bone marrow chimeras revealed that Nfkb1(SSAA/SSAA) FM B cells were completely unable to mediate T cell-dependent antibody responses. Nfkb1(SSAA) mutation decreased B cell antigen receptor (BCR) activation of NF-κB in FM B cells, which selectively blocked BCR stimulation of cell survival and antigen-induced differentiation into plasmablasts and germinal center B cells due to reduced expression of Bcl-2 family proteins and IRF4, respectively. In contrast, the antigen-presenting function of FM B cells and their BCR-induced migration to the follicle T cell zone border, as well as their growth and proliferation after BCR stimulation, were not affected. All of the inhibitory effects of Nfkb1(SSAA) mutation on B cell functions were rescued by normalizing NF-κB activation genetically. Our study identifies critical B cell-intrinsic functions for IKK-induced NF-κB1 p105 proteolysis in the antigen-induced survival and differentiation of FM B cells, which are essential for T-dependent antibody responses.

The BiP cochaperone ERdj4 is required for B cell development and function.

ERdj4 is a BiP cochaperone regulated by the unfolded protein response to facilitate degradation of unfolded and/or misfolded proteins in the endoplasmic reticulum. As the unfolded protein response plays a critical role in B cell maturation and antibody production, ERdj4 gene trap mice were generated to determine if this chaperone was required for B cell homeostasis. Homozygosity for the trapped allele resulted in hypomorphic expression of ERdj4 in bone marrow cells and abnormal development of hematopoietic lineages in the bone marrow. The number of myeloid cells was increased, while the number of erythroid and B lymphoid cells was reduced in ERdj4 gene trap mice compared to controls. An intrinsic B cell defect was identified that decreased survival of B cell precursors including large and small pre-B, and immature B cells. Consistent with impaired B lymphopoiesis, the number of mature follicular B cells was reduced in both the bone marrow and spleen of ERdj4 gene trap mice. Paradoxically, unchallenged ERdj4 gene trap mice showed non-specific hypergammaglobulinemia and gene trap B cells exhibited increased proliferation, survival and isotype switching in response to LPS stimulation. Although ERdj4 gene trap mice responded normally to T cell-independent antigen, they failed to mount a specific antibody response to T cell-dependent antigen in vivo. Collectively, these findings demonstrate that the chaperone activity of ERdj4 is required for survival of B cell progenitors and normal antibody production.

PP4 is essential for germinal center formation and class switch recombination in mice.

PP4 is a serine/threonine phosphatase required for immunoglobulin (Ig) VDJ recombination and pro-B/pre-B cell development in mice. To elucidate the role of PP4 in mature B cells, we ablated the catalytic subunit of murine PP4 in vivo utilizing the CD23 promoter and cre-loxP recombination and generated CD23crePP4F/F mice. The development of follicular and marginal zone B cells was unaffected in these mutants, but the proliferation of mature PP4-deficient B cells stimulated by in vitro treatment with either anti-IgM antibody (Ab) or LPS was partially impaired. Interestingly, the induction of CD80 and CD86 expression on these stimulated B cells was normal. Basal levels of serum Igs of all isotypes were strongly reduced in CD23crePP4F/F mice, and their B cells showed a reduced efficiency of class switch recombination (CSR) in vitro upon stimulation by LPS or LPS plus IL-4. When CD23crePP4F/F mice were challenged with either the T cell-dependent antigen TNP-KLH or the T cell-independent antigen TNP-Ficoll, or by H1N1 virus infection, the mutant animals failed to form germinal centers (GCs) in the spleen and the draining mediastinal lymph nodes, and did not efficiently mount antigen-specific humoral responses. In the resting state, PP4-deficient B cells exhibited pre-existing DNA fragmentation. Upon stimulation by DNA-damaging drug etoposide in vitro, mutant B cells showed increased cleavage of caspase 3. In addition, the mutant B cells displayed impaired CD40-mediated MAPK activation, abnormal IgM-mediated NF-κB activation, and reduced S phase entry upon IgM/CD40-stimulation. Taken together, our results establish a novel role for PP4 in CSR, and reveal crucial functions for PP4 in the maintenance of genomic stability, GC formation, and B cell-mediated immune responses.

Late stages of hematopoiesis and B cell lymphopoiesis are regulated by α-synuclein, a key player in Parkinson's disease

α-Synuclein plays a crucial role in Parkinson's disease and dementias defined as synucleinopathies. α-Synuclein is expressed in hematopoietic and immune cells, but its functions in hematopoiesis and immune responses are unknown. We utilized α-synuclein−/− (KO) mice to investigate its role in hematopoiesis and B cell lymphopoiesis. We demonstrated hematologic abnormalities including mild anemia, smaller platelets, lymphopenia but relatively normal early hematopoiesis in KO mice compared to wild-type (WT) as measured in hematopoietic stem cells and progenitors of the different cell lineages. However, the absolute number of B220+IgM+ B cells in bone marrow was reduced by 4-fold in KO mice (WT: 104±23×105 vs. KO: 27±5×105). B cells were also reduced in KO spleens associated with effacement of splenic and lymph node architecture. KO mice showed reduced total serum IgG but no abnormality in serum IgM was noted. When KO mice were challenged with a T cell-dependent antigen, production of antigen specific IgG1 and IgG2b was abolished, but antigen specific IgM was not different from WT mice. Our study shows hematologic abnormalities including anemia and smaller platelets, reduced B cell lymphopoiesis and defects in IgG production in the absence of α-synuclein. This is the first report to show an important role of α-synuclein late in hematopoiesis, B cell lymphopoiesis and adaptive immune response.

BAFF Binding to T Cell-Expressed BAFF-R Promotes Follicular Helper T Cell Proliferation and GC B Cell Responses.

Recent studies have defined a crucial role for the B cell-activating factor belonging to TNF family (BAFF) in promoting germinal center (GC) responses in mouse model. BAFF-deficient (BAFF-/-) mouse was defective in primary B cell survival and development, including a loss of transitional type 2, follicular, and marginal zone B cells. This fact prompted us to investigate the influence of BAFF on follicular helper T (Tfh) cells, another important subset that helps antibody production in GC. In vivo, various strains of mice were immunized with keyhole limpet hemocyanin (KLH) emulsified in CFA. We first observed that BAFF deficiency impairs GC B cell responses to T cell dependent antigens. We also found that BAFF-/- mice, but not APRIL-/- mice, have a defect on the generation of Tfh cells and antibody production. Similar to BAFF-/- mice, BR3-/- mice also showed almost none of Tfh cells in draining lymph node. While BCMA-/- or TACI-/- mice appeared to be normal or even higher percentage of Tfh cells in spleen and lymph node after antigen stimulation. Thus, BAFF might upregulate the Tfh cells via BR3, rather than BCMA or TACI, all of which are BAFF receptors. To rule out the influence of impaired B cell by BAFF, Bcl2 Tg and BAFF-/-Bcl2 Tg mice were employed for keeping survival B cells in BAFF deficient background. To the end, we found that lack of BAFF still caused impaired Tfh cell and antibody production. With a co-transfer experiment, we further comfirmed that BAFF is required for the differentiation of Tfh cells and production of GC B cells. In vitro, we demonstrated that BAFF increases IL-21 mRNA expression in CD4+ T cells, and IL-6 mRNA expression in B cells and dendritic cells. In summary, these findings provide evidence that BAFF promotes Tfh development, germinal center generation and pathogenesis of autoimmune diseases.

Concurrent Oral Sessions

Recent studies have defined a crucial role for the B cell-activating factor belonging to TNF family (BAFF) in promoting germinal center (GC) responses in mouse model. BAFF-deficient (BAFF-/-) mouse was defective in primary B cell survival and development, including a loss of transitional type 2, follicular, and marginal zone B cells. This fact prompted us to investigate the influence of BAFF on follicular helper T (Tfh) cells, another important subset that helps antibody production in GC. In vivo, various strains of mice were immunized with keyhole limpet hemocyanin (KLH) emulsified in CFA. We first observed that BAFF deficiency impairs GC B cell responses to T cell dependent antigens. We also found that BAFF-/- mice, but not APRIL-/- mice, have a defect on the generation of Tfh cells and antibody production. Similar to BAFF-/- mice, BR3-/- mice also showed almost none of Tfh cells in draining lymph node. While BCMA-/- or TACI-/- mice appeared to be normal or even higher percentage of Tfh cells in spleen and lymph node after antigen stimulation. Thus, BAFF might upregulate the Tfh cells via BR3, rather than BCMA or TACI, all of which are BAFF receptors. To rule out the influence of impaired B cell by BAFF, Bcl2 Tg and BAFF-/-Bcl2 Tg mice were employed for keeping survival B cells in BAFF deficient background. To the end, we found that lack of BAFF still caused impaired Tfh cell and antibody production. With a co-transfer experiment, we further comfirmed that BAFF is required for the differentiation of Tfh cells and production of GC B cells. In vitro, we demonstrated that BAFF increases IL-21 mRNA expression in CD4+ T cells, and IL-6 mRNA expression in B cells and dendritic cells. In summary, these findings provide evidence that BAFF promotes Tfh development, germinal center generation and pathogenesis of autoimmune diseases.

Pivotal role of STAT3 signaling in germinal center B cell and T follicular helper cell differentiation (IRC3P.458)

Abstract Germinal center (GC) B cells and T follicular helper (Tfh) cells are critical for long-lived plasma cell differentiation and high-affinity antibody production in response to T cell-dependent antigens. Previous studies demonstrated that GC formation was intact in the absence of STAT3 in B cells at day 12. However, emerging evidence suggests that IL-21/STAT3 signaling is a potent regulator for B cell differentiation. To better understand the role of STAT3 in the kinetics of GC formation and GC B cell response, we assessed GC B cells at consecutive time points following immunization with antigen OVA. In B cell conditional STAT3-dificient mice, fewer GC and GC B cells were generated upon immunization in the late phase (day 21) but not on day 14 compared with that of control mice. Increased cell death and decreased cell proliferation were found in the STAT3 deficient GC B cells. Consequently, plasma cell differentiation and antibody production were impaired in B cell STAT3-deficient mice. In addition, the Tfh cell response was correlated with the magnitude of the GC B cell response and significantly decreased in B cell STAT3-deficient mice. Furthermore, GC B cells and autoantibody production were also significantly decreased in autoreactive B cell STAT3-deficient mice after apoptotic cell immunization. These data provide new insights into the GC and Tfh differentiation and the function of STAT3 in humoral immune responses.

Phosphatidylcholine as a metabolic cue for determining B cell fate and function (LYM6P.774)

Abstract In activated B cells, increased production of phosphatidylcholine (PtdCho), the most abundant cellular phospholipid, is handled primarily by the CDP-choline pathway. Previous studies revealed that CD19Cre-mediated deletion of CTP:phosphocholine cytidylyltransferase α (CCTα), the rate-limiting enzyme in the CDP-choline pathway, led to augmented IgM secretion and reduced IgG production, consistent with defective germinal center reactions. To more specifically assess the influence of PtdCho on B cell fate during germinal center and long-term humoral responses, we examined immune responses in Cγ1Cre CCTαflox mice. Serum IgG1 was undetectable in naïve Cγ1Cre CCTαflox mice, while levels of IgM and other IgG subclasses were similar in naïve Cγ1Cre CCTαflox and control mice. Following immunization with T cell-dependent antigen NP-KLH, control mice predictively generated high titer IgG anti-NP. In contrast, IgG anti-NP titers were markedly reduced in immunized Cγ1Cre CCTαflox mice. Interestingly, though antigen-specific IgM responses were comparable between Cγ1Cre CCTαflox and control mice, the IgM anti-NP response in Cγ1Cre CCTαflox mice failed to increase in affinity. Lastly, the frequency of antigen-experienced NP-specific B cells and antibody-secreting cells (ASC) were both reduced in Cγ1Cre CCTαflox mice compared with controls. These data indicate that PtdCho plays a pivotal role in the generation and persistence of both germinal center B cells and ASC.

Revisiting the role of B cells in Chlamydia muridarum genital tract infection (MUC7P.753)

Abstract B cells can contribute to acquired immunity against intracellular bacteria, but do not usually participate in primary clearance. Using MHC class-II tetramers, we examined the endogenous CD4 T cell response to Chlamydia muridarum genital tract infection. Chlamydia-specific CD4 T cells expanded rapidly and persisted as a stable memory pool for several months after infection. While most lymph node Chlamydia-specific CD4 T cells expressed T-bet, a small percentage co-expressed Foxp3, and RORγt-expressing T cells were enriched within the reproductive tract. Local Chlamydia-specific CD4 T cell priming was markedly reduced in mice lacking B cells, and bacteria were able to disseminate to the peritoneal cavity, initiating a cellular infiltrate and ascites. However, bacterial dissemination also coincided with elevated systemic Chlamydia-specific CD4 T cell responses and resolution of primary infection. Together, these data reveal heterogeneity in pathogen-specific CD4 T cell responses within the genital tract and an unexpected requirement for B cells in regulating local T cell activation and bacterial dissemination during genital infection. We are currently focusing our efforts on understanding the mechanism underlying the function of B cells during primary Chlamydia infection. Our preliminary data suggest that antibody, but not B cell-dependent antigen presentation, is required for bacterial containment at local genital mucosa.

CRTC2 regulates miRNAs and binds to chromatin remodeling factors to control germinal center B cell fate (798.1)

When B cells are stimulated by T cell‐dependent antigens during an immune response, they form germinal centers (GCs) to undergo clonal expansion and affinity‐based selection of surface Ig proteins. GC B cells are highly proliferative and misregulation of normal GC processes results in hematologic malignancies. Our lab has shown that inactivation of CRTC2, a CREB transcriptional co‐activator, and the repression of its target genes are required for B cells to exit the GC and differentiate into plasma cells. CRTC2 is inactivated by a signaling pathway triggered by DNA double strand breaks during Ig gene remodeling. This inactivation process ends with the nuclear export of CRTC2, shutting down a gene program to enable GC B cells to differentiate into plasma cells. Despite the significance of this signaling pathway and its CRTC2‐regulated target genes, key details and mechanisms of CRTC2 regulation during B cell differentiation have not been fully explored. Using a bioinformatics‐coupled molecular approach, we identified multiple candidate CRTC2‐target microRNAs that could regulate GC B cell physiology. Our data also reveals that CRTC2 interacts with components of chromatin remodeling complexes at target promoters in GC B cells. Our findings predict that CRTC2, through its control of miRNA expression and interactions with co‐regulatory factors, regulates B cell development and lymphomagenesis.Grant Funding Source: Supported by R01CA90571, R01CA156674, P01GM081621 (all to M.A.T.) and T32‐CA009056 (to R.N.)

Murine complement receptor 1 is required for germinal center B cell maintenance but not initiation

Germinal centers are the anatomic sites for the generation of high affinity immunoglobulin expressing plasma cells and memory B cells. The germinal center B cells that are precursors of these cells circulate between the light zone B cell population that interact with antigen laden follicular dendritic cells (FDC) and the proliferative dark zone B cell population. Antigen retention by follicular dendritic cells is dependent on Fc receptors and complement receptors, and complement receptor 1 (Cr1) is the predominant complement receptor expressed by FDC. The newly created Cr1KO mouse was used to test the effect of Cr1-deficiency on the kinetics of the germinal center reaction and the generation of IgM and switched memory B cell formation. Immunization of Cr1KO mice with a T cell-dependent antigen resulted in the normal initial expansion of B cells with a germinal center phenotype however these cells were preferentially lost in the Cr1KO animal over time (days). Bone marrow chimera animals documented the surprising finding that the loss of germinal center B cell maintenance was linked to the expression of Cr1 on B cells, not the FDC. Cr1-deficiency further resulted in antigen-specific IgM titer and IgM memory B cell reductions, but not antigen-specific IgG after 35–37 days. Investigations of nitrophenyl (NP)-specific IgG demonstrated that Cr1 is not necessary for affinity maturation during the response to particulate antigen. These data, along with those generated in our initial description of the Cr1KO animal describe unique functions of Cr1 on the surface of both B cells and FDC.

Activation of B Cells by a Dendritic Cell-Targeted Oral Vaccine

Production of long-lived, high affinity humoral immunity is an essential characteristic of successful vaccination and requires cognate interactions between T and B cells in germinal centers. Within germinal centers, specialized T follicular helper cells assist B cells and regulate the antibody response by mediating the differentiation of B cells into memory or plasma cells after exposure to T cell-dependent antigens. It is now appreciated that local immune responses are also essential for protection against infectious diseases that gain entry to the host by the mucosal route; therefore, targeting the mucosal compartments is the optimum strategy to induce protective immunity. However, because the gastrointestinal mucosae are exposed to large amounts of environmental and dietary antigens on a daily basis, immune regulatory mechanisms exist to favor tolerance and discourage autoimmunity at these sites. Thus, mucosal vaccination strategies must ensure that the immunogen is efficiently taken up by the antigen presenting cells, and that the vaccine is capable of activating humoral and cellular immunity, while avoiding the induction of tolerance. Despite significant progress in mucosal vaccination, this potent platform for immunotherapy and disease prevention must be further explored and refined. Here we discuss recent progress in the understanding of the role of different phenotypes of B cells in the development of an efficacious mucosal vaccine against infectious disease.

Retinoic acid prevents mesenteric lymph node dendritic cells from inducing IL-13-producing inflammatory Th2 cells.

The vitamin A (VA) metabolite retinoic acid (RA) affects the properties of T cells and dendritic cells (DCs). In VA-deficient mice, we observed that mesenteric lymph node (MLN)-DCs induce a distinct inflammatory T helper type 2 (Th2)-cell subset that particularly produces high levels of interleukin (IL)-13 and tumor necrosis factor-α (TNF-α). This subset expressed homing receptors for skin and inflammatory sites, and was mainly induced by B220(-)CD8α(-)CD11b(+)CD103(-) MLN-DCs in an IL-6- and OX40 ligand-dependent manner, whereas RA inhibited this induction. The corresponding MLN-DC subset of VA-sufficient mice induced a similar T-cell subset in the presence of RA receptor antagonists. IL-6 induced this subset differentiation from naive CD4(+) T cells upon activation with antibodies against CD3 and CD28. Transforming growth factor-β inhibited this induction, and reciprocally enhanced Th17 induction. Treatment with an agonistic anti-OX40 antibody and normal MLN-DCs enhanced the induction of general inflammatory Th2 cells. In VA-deficient mice, proximal colon epithelial cells produced TNF-α that may have enhanced OX40 ligand expression in MLN-DCs. The repeated oral administrations of a T cell-dependent antigen primed VA-deficient mice for IL-13-dependent strong immunoglobulin G1 (IgG1) responses and IgE responses that caused skin allergy. These results suggest that RA inhibits allergic responses to oral antigens by preventing MLN-DCs from inducing IL-13-producing inflammatory Th2 cells.

Naive and memory human B cells have distinct requirements for STAT3 activation to differentiate into antibody-secreting plasma cells

Long-lived antibody memory is mediated by the combined effects of long-lived plasma cells (PCs) and memory B cells generated in response to T cell-dependent antigens (Ags). IL-10 and IL-21 can activate multiple signaling pathways, including STAT1, STAT3, and STAT5; ERK; PI3K/Akt, and potently promote human B cell differentiation. We previously showed that loss-of-function mutations in STAT3, but not STAT1, abrogate IL-10- and IL-21-mediated differentiation of human naive B cells into plasmablasts. We report here that, in contrast to naive B cells, STAT3-deficient memory B cells responded to these STAT3-activating cytokines, differentiating into plasmablasts and secreting high levels of IgM, IgG, and IgA, as well as Ag-specific IgG. This was associated with the induction of the molecular machinery necessary for PC formation. Mutations in IL21R, however, abolished IL-21-induced responses of both naive and memory human B cells and compromised memory B cell formation in vivo. These findings reveal a key role for IL-21R/STAT3 signaling in regulating human B cell function. Furthermore, our results indicate that the threshold of STAT3 activation required for differentiation is lower in memory compared with naive B cells, thereby identifying an intrinsic difference in the mechanism underlying differentiation of naive versus memory B cells.

Gpr97 is essential for the follicular versus marginal zone B-lymphocyte fate decision

Gpr97 is an orphan adhesion GPCR and is highly conserved among species. Up to now, its physiological function remains largely unknown. Here, we show that Gpr97 deficiency results in an extensive reduction in B220+ lymphocytes in mice. More intensive analyses reveal an expanded marginal zone but a decreased follicular B-cell population in Gpr97−/−spleen, which displays disorganized architecture characterized by diffuse, irregular B-cell areas and the absence of discrete perifollicular marginal and mantle zones. In vivo functional studies reveal that the mutant mice could generate antibody responses to T cell-dependent and independent antigens, albeit enhanced response to the former and weakened response to the latter. By screening for the molecular events involved in the observed phenotypes, we found that lambda 5 expression is downregulated and its upstream inhibitor Aiolos is increased in the spleen of mutant mice, accompanied by significantly enhanced phosphorylation and nuclear translocation of cAMP response element-binding protein. Interestingly, increased constitutive Nf-κb p50/p65 expression and activity were observed in Gpr97−/− spleen, implicating a crucial role of Gpr97 in regulating Nf-κb activity. These findings uncover a novel biological function of Gpr97 in regulating B-cell development, implying Gpr97 as a potential therapeutic target for treatment of immunological disorders.

A Humanized Monoclonal Antibody Specific for Invariant Natural Killer T (iNKT) Cells for In Vivo Depletion

Invariant Natural Killer T (iNKT) cells are a subset of T cells recognizing glycolipid antigens presented by CD1d. Human iNKT cells express a conserved T cell receptor (TCR)-α chain (Vα24-Jα18) paired with a specific beta chain, Vβ11. The cells are both innate-like, with rapid cytokine release, and adaptive-like, including thymic positive selection. Over activation of iNKT cells can mediate tissue injury and inflammation in multiple organ systems and play a role in mediating the pathology associated with clinically important inflammatory diseases. At the same time, iNKT cell activation can play a role in protecting against infectious disease and cancer or modulate certain autoimmune diseases through its impact on both the innate and adaptive immune system. This suggests that approaches to cause iNKT cell reduction and/or depletion could treat inflammatory diseases while approaches to promote activation may have therapeutic potential in certain infections, cancer or autoimmune disease. This report summarizes the characterization of a humanized monoclonal depleting antibody (NKTT120) in the cynomolgus macaque. NKTT120 is being developed to treat iNKT mediated inflammation that is associated with chronic inflammatory conditions like sickle cell disease and asthma. NKTT120 binds to human iTCRs and to FCγRI and FCγRIII and has been shown to kill target cells in an ADCC assay at low concentrations consistent with the FCγR binding. iNKT cells were depleted within 24 hours in cynomolgus macaques, but T cell, B cell, and NK cell frequencies were unchanged. iNKT cell recovery was dose and time dependent. T cell dependent antigen responses were not impaired by NKTT120 mediated iNKT depletion as measured by response to KLH challenge. NKTT120 administration did not induce an inflammatory cytokine release at doses up to 10 mg/kg. These data support the use of NKTT120 as an intervention in inflammatory diseases where iNKT reduction or depletion could be beneficial.

T cell–independent B cell activation induces immunosuppressive sialylated IgG antibodies

Antigen-specific Abs are able to enhance or suppress immune responses depending on the receptors that they bind on immune cells. Recent studies have shown that pro- or antiinflammatory effector functions of IgG Abs are also regulated through their Fc N-linked glycosylation patterns. IgG Abs that are agalactosylated (non-galactosylated) and asialylated are proinflammatory and induced by the combination of T cell-dependent (TD) protein antigens and proinflammatory costimulation. Sialylated IgG Abs, which are immunosuppressive, and Tregs are produced in the presence of TD antigens under tolerance conditions. T cell-independent (TI) B cell activation via B cell receptor (BCR) crosslinking through polysaccharides or via BCR and TLR costimulation also induces IgG Abs, but the Fc glycosylation state of these Abs is unknown. We found in mouse experiments that TI immune responses induced suppressive sialylated IgGs, in contrast to TD proinflammatory Th1 and Th17 immune responses, which induced agalactosylated and asialylated IgGs. Transfer of low amounts of antigen-specific sialylated IgG Abs was sufficient to inhibit B cell activation and pathogenic immune reactions. These findings suggest an immune regulatory function for TI immune responses through the generation of immunosuppressive sialylated IgGs and may provide insight on the role of TI immune responses during infection, vaccination, and autoimmunity.

Antibody Avidity in Humoral Immune Responses in Bangladeshi Children and Adults following Administration of an Oral Killed Cholera Vaccine

Antibody avidity for antigens following disease or vaccination increases with affinity maturation and somatic hypermutation. In this study, we followed children and adults in Bangladesh for 1 year following oral cholera vaccination and measured the avidity of antibodies to the T cell-dependent antigen cholera toxin B subunit (CTB) and the T cell-independent antigen lipopolysaccharide (LPS) in comparison with responses in other immunological measurements. Children produced CTB-specific IgG and IgA antibodies of high avidity following vaccination, which persisted for several months; the magnitudes of responses were comparable to those seen in adult vaccinees. The avidity of LPS-specific IgG and IgA antibodies in vaccinees increased significantly shortly after the second dose of vaccine but waned rapidly to baseline levels thereafter. CTB-specific memory B cells were present for only a short time following vaccination, and we did not find significant memory B cell responses to LPS in any age group. For older children, there was a significant correlation between CTB-specific memory T cell responses after the second dose of vaccine and CTB-specific IgG antibody avidity indices over the subsequent year. These findings suggest that vaccination induces a longer-lasting increase in the avidity of antibodies to a T cell-dependent antigen than is measured by a memory B cell response to that antigen and that early memory T cell responses correlate well with the subsequent development of higher-avidity antibodies.

Antigenic liposomes displaying CD22 ligands induce antigen-specific B cell apoptosis

Antibodies confer humoral immunity but can also be harmful when they target an autoantigen, alloantigen, allergen, or biotherapeutic. New strategies are needed for antigen-specific suppression of undesired antibody responses, particularly to T cell-dependent protein antigens, because they elicit T cell help. Here we show that liposomal nanoparticles, displaying both antigen and glycan ligands of the inhibitory coreceptor CD22, induce a tolerogenic program that selectively causes apoptosis in mouse and human B cells. These SIGLEC-engaging tolerance-inducing antigenic liposomes (STALs, where SIGLEC is defined as sialic acid-binding Ig-like lectin) induced robust antigen-specific tolerance to protein antigens in mice, preventing subsequent immune response to challenge with the same antigen. Since development of inhibitory antibodies to FVIII is a serious problem in treatment of hemophilia A patients, we investigated the potential of this approach for inducing tolerance to FVIII in a hemophilia mouse model. STALs prevented formation of inhibitory FVIII antibodies, allowing for effective administration of FVIII to hemophilia mice to prevent bleeding. These findings suggest that STALs could be used to eliminate or prevent harmful B cell-mediated immune responses.