By-passing in vitro screening--next generation sequencing technologies applied to antibody display and in silico candidate selection.

In recent years, unprecedented DNA sequencing capacity provided by next generation sequencing (NGS) has revolutionized genomic research. Combining the Illumina sequencing platform and a scFv library designed to confine diversity to both CDR3, >1.9 × 10(7) sequences have been generated. This approach allowed for in depth analysis of the library's diversity, provided sequence information on virtually all scFv during selection for binding to two targets and a global view of these enrichment processes. Using the most frequent heavy chain CDR3 sequences, primers were designed to rescue scFv from the third selection round. Identification, based on sequence frequency, retrieved the most potent scFv and valuable candidates that were missed using classical in vitro screening. Thus, by combining NGS with display technologies, laborious and time consuming upfront screening can be by-passed or complemented and valuable insights into the selection process can be obtained to improve library design and understanding of antibody repertoires.

An amyloid beta vaccine that safely drives immunity to a key pathological species in Alzheimer's disease: pyroglutamate amyloid beta.

Pyroglutamate amyloid beta3-42 (pGlu-Abeta3-42), a highly amyloidogenic and neurotoxic form of Abeta, is N-terminally truncated to form a pyroglutamate and has recently been proposed as a key target for immunotherapy. Optimized ACI-24, a vaccine in development for the treatment and prevention of Alzheimer's disease, focuses the antibody response on the first 15 N-terminal amino acids of Abeta (Abeta1-15). Importantly, clinical data with an initial version of ACI-24 incorporating Abeta1-15, established the vaccine's safety and tolerability with evidence of immunogenicity. To explore optimized ACI-24's capacity to generate antibodies to pGlu-Abeta3-42, pre-clinical studies were carried out. Vaccinating mice and non-human primates demonstrated that optimized ACI-24 was well-tolerated and induced an antibody response against Abeta1-42 as expected, as well as high titres of IgG reactive with pyroGlu-Abeta. Epitope mapping of the polyclonal response confirmed these findings revealing broad coverage of epitopes particularly for Abeta peptides mimicking where cleavage occurs to form pGlu-Abeta3-42. These data are in striking contrast to results obtained with other clinically tested Abeta targeting vaccines which generated restricted and limited antibody diversity. Taken together, our findings demonstrate that optimized ACI-24 vaccination represents a breakthrough to provide a safe immune response with a broader Abeta sequence recognition compared to previously tested vaccines, creating binders to pathogenic forms of Abeta important in pathogenesis including pGlu-Abeta3-42.

Follicular dendritic cells help resting B cells to become effective antigen-presenting cells: induction of B7/BB1 and upregulation of major histocompatibility complex class II molecules.

This study was designed to investigate whether follicular dendritic cells (FDC) can activate B cells to a state in which they can function as effective antigen-presenting cells (APC). High buoyant density (i.e., resting) B cells specific for 2,4-dinitro-fluorobenzene (DNP) were incubated with DNP-ovalbumin (OVA) bearing FDC, after which their capacity to process and present to an OVA-specific T cell clone was assessed. The efficacies of alternative sources of antigen and activation signals in the induction of B cell APC function were compared with those provided by FDC. Only FDC and Sepharose beads coated with anti-immunoglobulin (Ig)kappa monoclonal antibody provided the necessary stimulus. FDC carrying inappropriate antigens also induced B cell APC function in the presence of exogenous DNP-OVA. However, in circumstances where soluble DNP-OVA was limiting, FDC bearing complexes containing DNP, which could crosslink B cell Ig receptors, induced the most potent APC function. Analysis by flow cytometry revealed that within 24 h of coculture with FDC, a significant percentage of B cells increased in size and expressed higher levels of major histocompatibility complex class II. By 48 h, an upregulation of the costimulatory molecule, B7/BB1, occurred, but only when exposed to the FDC bearing DNP. Taken together, the results demonstrate that FDC have the capacity to activate resting B cells to a state in which they can function as APC for T cells. The stimuli that FDC provide may include: (a) an antigen-dependent signal that influences the upregulation of B7/BB1; and (b) possibly a signal independent of crosslinking mIg that results in Ig internalization. The relevance of these findings to the formation of germinal centers and maintenance of the humoral response is discussed.

Impaired mucosal immune responses in interleukin 4-targeted mice.

Interleukin 4-targeted (IL-4-/-) mice are defective in T helper (Th)2 cytokine production as determined after nematode infection. As Th2 cells appear to be selectively induced by oral immunization we investigated the ability of IL-4-/- mice to respond to perorally administered antigen. We found that IL-4-/- mice failed to respond to soluble protein antigens given perorally together with cholera toxin (CT) as a mucosal adjuvant. In contrast to wild-type mice no or poor anti-keyhole limpet hemocyanin (KLH) or anti-ovalbumin (OVA) B cell responses were observed in gut lamina propria, spleen, or serum of IL-4-/- mice after oral immunization. In addition, mucosal immunization failed to stimulate antigen-specific T cell responses in these mice. The lack of responsiveness was specific for mucosal administration of antigen and was not seen after intravenous injections with antigen and CT-adjuvant. The systemic adjuvant effect of CT was not impaired in IL-4-/- mice as evidenced by the strong enhancement of anti-KLH responses after intravenous immunization with KLH plus CT as opposed to KLH alone. However, CT as an immunogen, in contrast to KLH or OVA, stimulated significant mucosal and systemic immune responses in IL-4-/- mice after oral immunization. Both serum and intestinal IgA anti-CT antibodies were demonstrable in IL-4-/- mice as well as in wild-type mice. Total IgA levels in gut lavage and in serum of immunized IL-4-/- mice were of similar magnitude as in wild-type mice, suggesting that the ability of naive B cells to undergo isotype switch-differentiation from IgM to IgA in IL-4-/- mice did not appear to be impaired. Immunohistochemical analysis of Peyer's patches demonstrated a complete inability to form germinal centers in IL-4-/- mice in contrast to wild-type mice. Our data suggest that IL-4-/- mice are unable to respond to oral/mucosal immunization due to a failure to stimulate antigen-specific cells required to induce germinal center reactions in the Peyer's patches. Our findings demonstrate that IL-4 and probably functional Th2 cells are required for induction of gut mucosal antibody responses.

Interleukin 6 influences germinal center development and antibody production via a contribution of C3 complement component.

Mice rendered deficient for interleukin (IL) 6 by gene targeting were evaluated for their response to T cell-dependent antigens. Antigen-specific immunoglobulin (Ig)M levels were unaffected whereas all IgG isotypes showed varying degrees of alteration. Germinal center reactions occurred but remained physically smaller in comparison to those in the wild-type mice. This concurred with the observations that molecules involved in initial signaling events leading to germinal center formation were not altered (e.g., B7.2, CD40 and tumor necrosis factor R1). T cell priming was not impaired nor was a gross imbalance of T helper cell (Th) 1 versus Th2 cytokines observed. However, B7.1 molecules, absent from wild-type counterparts, were detected on germinal center B cells isolated from the deficient mice suggesting a modification of costimulatory signaling. A second alteration involved impaired de novo synthesis of C3 both in serum and germinal center cells from IL-6-deficient mice. Indeed, C3 provided an essential stimulatory signal for wild-type germinal center cells as both monoclonal antibodies that interrupted C3-CD21 interactions and sheep anti-mouse C3 antibodies caused a significant decrease in antigen-specific antibody production. In addition, germinal center cells isolated from C3-deficient mice produced a similar defect in isotype production. Low density cells with dendritic morphology were the local source of IL-6 and not the germinal center lymphocytes. Adding IL-6 in vitro to IL-6-deficient germinal center cells stimulated cell cycle progression and increased levels of antibody production. These findings reveal that the germinal center produces and uses molecules of the innate immune system, evolutionarily pirating them in order to optimally generate high affinity antibody responses.

The sequential role of lymphotoxin and B cells in the development of splenic follicles.

The transfer of lymphocytes into severe combined immunodeficiency (SCID) mice induces a series of histological changes in the spleen, including the appearance of mature follicular dendritic cells (FDCs). Studies were undertaken to clarify the role of lymphotoxin (LT) in this process. The results show that SCID mice have a small and partially differentiated white pulp containing marginal zone and interdigitating dendritic cells, but lacking FDCs. Transferred spleen cells can segregate into T and B cell areas shortly after their injection to SCID mice. This ability is dependent on signaling through LT-beta receptor (LT-betaR), since blocking ligand-receptor interaction in recipient SCID mice ablates the capacity of the transferred cells to segregate. A week after lymphocyte transfer, host-derived FDCs appeared in the reconstituted SCID mice. This induction of FDCs is dependent on LT-betaR signaling by B cells since LT-alpha-/- B cells are incapable of inducing development of FDCs in SCID mice, even after cotransfer of LT-alpha+/+ T cells. Therefore, LT plays at least two discrete roles in splenic organization. First, it appears that LT induces the differentiation of the white pulp to create sites for lymphocyte segregation. Second, LT expression by B cells drives the maturation of FDCs and the organization of B cell follicles.

Germinal center formation and local immunoglobulin E (IgE) production in the lung after an airway antigenic challenge.

Airway inflammation plays a central role in the pathogenesis of asthma. However, the precise contribution of all cell types in the development and maintenance of airway hyperreactivity and histopathology during allergic inflammation remains unclear. After sensitization of mice in the periphery, challenge by multiple intratracheal (i.t.) instillations of ovalbumin (OVA) results in eosinophilia, mononuclear cell infiltration, and airway epithelial changes analogous to that seen in asthma (Blyth, D.I., M.S. Pedrick, T.J. Savage, E.M. Hessel, and D. Fattah. 1996. Am. J. Respir. Cell Mol. Biol. 14:425-438). To investigate further the nature of the cellular infiltrate, lungs from OVA-versus saline-treated mice were processed for histology and immunohistochemistry. One of the most striking features observed was the formation of germinal centers within the parenchyma of the inflamed lungs. In addition, follicular dendritic cells (FDCs) bearing OVA on their plasma membranes appeared and, adjacent to these sites, OVA-specific IgG1-, IgE-, and IgA-producing plasma cells emerged. To confirm that antigen-specific immunoglobulins (Ig) were being produced within the parenchyma, plasma cell number and antibody production were quantitated in vitro after isolation of cells from the lung. These assays confirmed that the isotypes observed in situ were a secreted product. As IgE-dependent mechanisms have been implicated as being central to the pathogenesis of bronchial asthma, airway hyperresponsiveness was evaluated. The mice undergoing lung inflammation were hyperresponsive, while the control group remained at baseline. These data demonstrate that antigen-driven differentiation of B cells via induction of an FDC network and germinal centers occurs in the parenchyma of inflamed lungs. These germinal centers would then provide a local source of IgE-secreting plasma cells that contribute to the release of factors mediating inflammatory processes in the lung.

A member of the dendritic cell family that enters B cell follicles and stimulates primary antibody responses identified by a mannose receptor fusion protein.

Dendritic cells (DCs) are known to activate naive T cells to become effective helper cells. In addition, recent evidence suggests that DCs may influence naive B cells during the initial priming of antibody responses. In this study, using three-color confocal microscopy and three-dimensional immunohistograms, we have observed that in the first few days after a primary immunization, cells with dendritic morphology progressively localize within primary B cell follicles. These cells were identified by their ability to bind a fusion protein consisting of the terminal cysteine-rich portion of the mouse mannose receptor and the Fc portion of human immunoglobulin (Ig)G1 (CR-Fc). In situ, these CR-Fc binding cells express major histocompatibility complex class II, sialoadhesin, and CD11c and are negative for other markers identifying the myeloid DC lineage, such as (CD11b), macrophages (F4/80), follicular DCs (FDC-M2), B cells (B220), and T cells (CD4). Using CR-Fc binding capacity and flow cytometry, the cells were purified from the draining lymph nodes of mice 24 h after immunization. When injected into naive mice, these cells were able to prime T cells as well as induce production of antigen-specific IgM and IgG1. Furthermore, they produced significantly more of the lymphocyte chemoattractant, macrophage inflammatory protein (MIP)-1alpha, than isolated interdigitating cells. Taken together, these results provide evidence that a subset of DCs enters primary follicles, armed with the capacity to attract and provide antigenic stimulation for T and B lymphocytes.

Mature follicular dendritic cell networks depend on expression of lymphotoxin beta receptor by radioresistant stromal cells and of lymphotoxin beta and tumor necrosis factor by B cells.

The formation of germinal centers (GCs) represents a crucial step in the humoral immune response. Recent studies using gene-targeted mice have revealed that the cytokines tumor necrosis factor (TNF), lymphotoxin (LT) alpha, and LTbeta, as well as their receptors TNF receptor p55 (TNFRp55) and LTbetaR play essential roles in the development of GCs. To establish in which cell types expression of LTbetaR, LTbeta, and TNF is required for GC formation, LTbetaR-/-, LTbeta-/-, TNF-/-, B cell-deficient (BCR-/-), and wild-type mice were used to generate reciprocal or mixed bone marrow (BM) chimeric mice. GCs, herein defined as peanut agglutinin-binding (PNA+) clusters of centroblasts/centrocytes in association with follicular dendritic cell (FDC) networks, were not detectable in LTbetaR-/- hosts after transfer of wild-type BM. In contrast, the GC reaction was restored in LTbeta-/- hosts reconstituted with either wild-type or LTbetaR-/- BM. In BCR-/- recipients reconstituted with compound LTbeta-/-/BCR-/- or TNF-/-/BCR-/- BM grafts, PNA+ cell clusters formed in splenic follicles, but associated FDC networks were strongly reduced or absent. Thus, development of splenic FDC networks depends on expression of LTbeta and TNF by B lymphocytes and LTbetaR by radioresistant stromal cells.

Crucial role of tumor necrosis factor receptor 1 expression on nonhematopoietic cells for B cell localization within the splenic white pulp.

During immune responses the initial activation of B cells takes place in T cell zones of periarteriolar lymphoid sheaths (PALS) of the splenic white pulp. After initial activation, B cells migrate into the primary follicles and, in association with follicular dendritic cells (FDCs), undergo clonal expansion and differentiation giving rise to germinal centers (GCs). Peanut agglutinin binding (PNA+) cells of the GC differentiate further into memory or plasma cells. Here we report that in tumor necrosis factor receptor 1-deficient mice (TNFR1(-/-)), the location of B cells was altered and that plasma cells were abnormally distributed in the splenic PALS. In contrast to lymphotoxin alpha-deficient mice (LTalpha-/-), bone marrow or fetal liver transplantation did not correct the abnormal organization of the spleen, location of B cells, the lack of an FDC network, nor the antibody response in TNFR1(-/-) mice. These results argue for a crucial role of TNFR1 expression on nonhematopoietic cells for the maintenance of the splenic architecture and proper B cell location. In addition, the lack in development of an FDC network after adoptive transfer suggests that either FDCs are not of bone marrow origin or that they depend on signals from nonhematopoietic cells for maturation.

Differentiation of follicular dendritic cells and full antibody responses require tumor necrosis factor receptor-1 signaling.

Using mice double deficient for tumor necrosis factor (TNF) and lymphotoxin alpha (LT alpha), we demonstrated that TNF and/or LT alpha are necessary for development of a normal splenic microarchitecture and for isotype switch after immunization with sheep red blood cells (SRBC). In the present study, we extended these observations by determining which TNF receptor (TNFR) is involved in morphological and functional differentiation of the spleen. Spleen morphology and antibody response were investigated in wild-type, TNFR1-/-, TNFR2-/- and TNF/LT alpha-/- mice immunized with SRBC. TNF/LT alpha-/- mice, which have a complete disruption of the TNF/LT alpha signaling system including the LT beta-receptor pathway, displayed an abnormal microarchitecture, and isotype switch did not take place. TNFR1-/- and TNFR2-/- mice displayed a normal spleen microarchitecture and mounted an IgM and IgG antibody response to SRBC. However, the IgG production in TNFR1-/- mice was minimal, with citers leveling off 6 d after immunization. In this strain, immunofluorescence revealed a lack of follicular dendritic cells (FDC) network, detected with FDC-M1 as well as anti-CR1, and a lack of germinal centers, detected with peanut agglutinin. In conclusion, whereas normal splenic microarchitecture and isotype switch might require the LT beta receptor, differentiation of FDC network, development of germinal centers, and full IgG response depend on signaling via TNFR1.

Tumor necrosis factor receptor-1 signaling is required for differentiation of follicular dendritic cells, germinal center formation, and full antibody responses.

Using mice double deficient for tumor necrosis factor and lymphotoxin alpha (TNF/LT alpha-/-) we have demonstrated that TNF and/or LT alpha are important for morphogenesis of secondary lymphoid organs and for T-cell-dependent antibody responses. In the present study we attempted to identify the receptors involved in those functions of TNF and LT alpha. Spleen morphology and antibody responses were investigated in wild-type, TNFR1-/-, TNFR2-/-, and TNF/LT alpha-/- mice immunized with SRBC. TNF/LT alpha-/- mice, which have a complete disruption of the TNF/LT alpha signaling system including the lymphotoxin beta (LT beta) receptor pathway, displayed an abnormal splenic microarchitecture and isotype switch did not take place. TNFR1-/- and TNFR2-/- mice displayed a normal splenic morphology and mounted an IgM and IgG antibody response to SRBC. However, the IgG production in TNFR1-/- mice was abnormal, with titers leveling off after 6 days following primary immunization, and with a minimal response to a second antigen challenge. Immunofluorescence analysis of spleen sections revealed in this strain a lack of follicular dendritic cell (FDC) network and of germinal centers. In conclusion, while normal splenic microarchitecture and isotype switch might require the LT beta receptor, differentiation of the FDC network, development of germinal centers, a sustained IgG response, and probably the development of memory cells depend on signaling via TNFR1.

The physiology of murine germinal center reactions.

Germinal center responses are the mechanism that the immune system uses normally to generate high affinity antigen-specific B-cell receptors and secreted immunoglobulins. Genetically altered mice have provided powerful tools for dissecting the physiology of these germinal center responses. In this review, we have attempted to summarize information from various sources and interpret the new observations based on what was previously known. A section is included to review the basic anatomy of the relevant structures in lymph node and spleen. A summary of the mutant mice producing a phenotype where germinal center responses are altered is also furnished. This review is aimed at providing useful information to those working in this field as well as those wishing to understand more about in vivo immunology.

The dynamic structure of the germinal center.

Analysis of germinal centers (GCs) in chronically inflamed human tonsils has led to the dogma that GCs contain two compartments with separate functions: a dark zone where B cells proliferate and hypermutate; and a light zone where selection and differentiation occur. However, here Stephanie Camacho and colleagues discuss immunohistological analysis of splenic GCs arising de novo that reveal a more plastic structure.

The lymphotoxin beta receptor controls organogenesis and affinity maturation in peripheral lymphoid tissues.

Lymphotoxin beta receptor (LTbetaR)-/- mice were created by gene targeting. LTbetaR-/- mice lacked Peyer's patches, colon-associated lymphoid tissues, and all lymph nodes. Mucosa patrolling alphaEbeta7high integrin+ T cells were virtually absent. Spleens lost marginal zones; T/B cell segregation and follicular dendritic cell networks were absent. Peanut agglutinin+ cells were aberrantly detectable around central arterioles. In contrast to TNF receptor p55-/- mice, antibody affinity maturation was impaired. Since LTbetaR-/- mice exhibit distinct defects when compared to LTalpha-/- and LTbeta-/- mice, it is suggested that the LTbetaR integrates signals from other TNF family members. Thus, the LTbetaR proves pivotal for the ontogeny of the secondary lymphoid tissues. Furthermore, affinity maturation is dependent on LTalpha1beta2 rather than on LTalpha3.

B-cell-specific coactivator OBF-1/OCA-B/Bob1 required for immune response and germinal centre formation.

The B-lymphocyte-specific transcriptional factor called Oct binding factor (OBF)-1, OCA-B or Bob1 (refs 1-3) is thought to be involved in the transcription of immunoglobulin genes through recruitment to the highly conserved octamer site of immunoglobulin promoters, mediated by either Oct-1 or Oct-2. To define the in vivo role of OBF-1 we have used gene targeting in embryonic stem cells to generate mice lacking the coactivator OBF-1. Such OBF-1-/- mice are born normally, are fertile and seem healthy, and surprisingly, rearrangement and transcription of immunoglobulin genes are largely unaffected. However, mice deficient in OBF-1 have reduced numbers of mature B cells and a severe reduction in the number of recirculating B cells, but otherwise show normal B-cell differentiation. Serum IgA and particularly IgG levels are greatly reduced. If mutant mice are immunized with either a thymus-independent or a thymus-dependent antigen, their immune responses are dramatically weakened. Strikingly, germinal centres completely fail to develop after immunization with thymus-dependent antigen. Our results demonstrate that in vivo OBF-1 is not required for initial transcription of immunoglobulin genes or for B cell development, but instead is essential for the response of B cells to antigens, and is required for the formation of germinal centres.

Enhanced follicular dendritic cell-B cell interaction in HIV and SIV infections and its potential role in polyclonal B cell activation.

Human immunodeficiency virus (HIV) infections have been characterized by both polyclonal B-cell activation and enhanced responsiveness to B-cell growth factors on one hand and the loss of specific antibody (Ab) responses and refractoriness to the normal signals for B-cell activation on the other. Histopathological studies of lymph node from HIV- and simian immunodeficiency virus (SIV)-infected individuals have indicated initial follicular hyperplasia and the appearance of large irregular germinal centers that undergo progressive involution concomitant with follicular dendritic-cell (FDC) disruption. During this process, follicular dendritic-cell-enriched lymph-node-cell cultures exhibit increased ability to induce cluster formation ("in vitro germinal centers"), lymphocyte proliferation and antibody production compared to uninfected controls. This paper discusses how enhanced FDC-B-cell interaction within SIV-infected germinal centers may result in a reduced ability to select high-affinity B cells and alter the dynamics of antibody-producing-cell and memory-cell generation resulting in the observed hyperactivity.