Glycan-Reactive Innate-like B Cells and Developmental Checkpoints

Using an Ig H chain conferring specificity for N-acetyl-d-glucosamine (GlcNAc), we developed transgenic (VHHGAC39 TG) mice to study the role of self-antigens in GlcNAc-reactive B-1 B cell development. In VHHGAC39 TG mice, GlcNAc-reactive B-1 B cell development during ontogeny and in adult bone marrow was normal. However, adult TG mice exhibited a block at transitional-2 immature B cell stages, resulting in impaired allelic exclusion and accumulation of a B cell subset coexpressing endogenous Ig gene rearrangements. Similarly, VHHGAC39 B cell fitness was impeded compared with non-self-reactive VHJ558 B TG cells in competitive mixed bone marrow chimeras. Nonetheless, adult VHHGAC39 mice immunized with Streptococcus pyogenes produce anti-GlcNAc Abs. Peritoneal cavity B cells transferred from VHHGAC39 TG mice into RAG-/- mice also exhibited robust expansion and anti-GlcNAc Ab production. However, chronic treatment of young VHHGAC39 mice with GlcNAc-specific mAbs leads to lower GlcNAc-binding B cell frequencies while increasing the proportion of GlcNAc-binding B1-a cells, suggesting that Ag masking or clearance of GlcNAc Ags impedes maturation of newly formed GlcNAc-reactive B cells. Finally, BCR H chain editing promotes expression of endogenous nontransgenic BCR alleles, allowing potentially self-reactive TG B cells to escape anergy or deletion at the transitional stage of precursor B cell development. Collectively, these observations indicate that GlcNAc-reactive B cell development is sensitive to the access of autologous Ags.

B-1 B Cell-Derived Natural Antibodies against N-Acetyl-d-Glucosamine Suppress Autoimmune Diabetes Pathogenesis

Environmental factors and host microbiota strongly influence type 1 diabetes (T1D) progression. We report that neonatal immunization with group A Streptococcus suppresses T1D development in NOD mice by promoting clonal expansion of N-acetyl-d-glucosamine (GlcNAc)-specific B-1 B cells that recognize pancreatic β cell-derived Ags bearing GlcNAc-containing posttranslational modifications. Early exposure to Lancefield group A cell-wall carbohydrate Ags increased production of GlcNAc-reactive serum Abs and enhanced localization of innate-like GlcNAc-specific B cells to pancreatic tissue during T1D pathogenesis. We show that B-1 B cell-derived GlcNAc-specific IgM engages apoptosis-associated β cell Ags, thereby suppressing diabetogenic T cell activation. Likewise, adoptively transferring GlcNAc-reactive B-1 B cells significantly delayed T1D development in naive recipients. Collectively, these data underscore potentially protective involvement of innate-like B cells and natural Abs in T1D progression. These findings suggest that previously reported associations of reduced T1D risk after GAS infection are B cell dependent and demonstrate the potential for targeting the natural Ab repertoire in considering therapeutic strategies for T1D.

Crystal structure and induced stability of trimeric BxpB: implications for the assembly of BxpB-BclA complexes in the exosporium of Bacillus anthracis

The outermost exosporium layer of Bacillus anthracis spores, the causative agents of anthrax, is comprised of a basal layer and an external hair-like nap. The nap includes filaments composed of trimers of the collagen-like glycoprotein BclA. Essentially all BclA trimers are attached to the spore in a process in which part of the 38-residue amino-terminal domain (NTD) of BclA forms an extremely stable interaction with the basal layer protein BxpB. Evidence indicates that the BclA-BxpB interaction is direct and requires trimeric BxpB. To further investigate the nature of the BclA-BxpB interaction, we determined the crystal structure of BxpB. The structure was trimeric with each monomer consisting of 11 β strands with connecting loops. The structure did not include apparently disordered amino acids 1-19, which contain the only two cysteine residues of the 167-residue BxpB. The orientation of the structure reveals regions of BxpB that could be involved in interacting with the BclA NTD and with adjacent cysteine-rich proteins in the basal layer. Furthermore, the BxpB structure closely resembles that of the 134-residue carboxyl-terminal domain of BclA, which forms trimers that are highly resistant to heat and detergent. We demonstrated that BxpB trimers do not share this resistance. However, when BxpB trimers are mixed with a peptide containing residues 20-38 of BclA, they form a complex that is as stable as BclA-BxpB complexes extracted from spores. Together, our results provide new insights into the mechanism of BclA-BxpB attachment and incorporation into the exosporium. IMPORTANCE The B. anthracis exosporium plays major roles in spore survival and infectivity, but the complex mechanism of its assembly is poorly understood. Key steps in this process are the stable attachment of collagen-like BclA filaments to the major basal layer structural protein BxpB and the insertion of BxpB into an underlying basal layer scaffold. The goal of this study is to further elucidate these interactions thereby advancing our understanding of exosporium assembly, a process shared by many spore-forming bacteria including important human pathogens.

Alloreactivity and autoreactivity converge to support B cell epitope targeting in transplant rejection

Antibody (Ab) responses against human leukocyte antigen (HLA) proteins mismatched between donor and recipient are leading cause of allograft loss in kidney transplantation. However, therapies targeting alloreactive B cell and Ab-secreting cell (ASC) are lacking, motivating the need to understand how to prevent and abrogate these alloresponses. Using molecular, structural, and proteomic techniques, we profiled the B cell response in a kidney transplant recipient with antibody-mediated rejection and graft loss. We found that this response spanned the rejected organ and peripheral blood, stimulated the differentiation of multiple B cell subsets, and produced a high-affinity, donor-specific, anti-HLA response. We found epitopic immunodominance that relied on highly exposed, solvent-accessible mismatched HLA residues as well as structural and biomolecular evidence of autoreactivity against the recipient's self-HLA allele. These alloreactive and autoreactive signatures converged in the recipient's circulating donor-specific Ab repertoire, suggesting that rejection requires both the recognition of non-self and breaches of tolerance to lead to alloinjury and graft loss.

GPR183 Is Dispensable for B1 Cell Accumulation and Function, but Affects B2 Cell Abundance, in the Omentum and Peritoneal Cavity

B1 cells constitute a specialized subset of B cells, best characterized in mice, which is abundant in body cavities, including the peritoneal cavity. Through natural and antigen-induced antibody production, B1 cells participate in the early defense against bacteria. The G protein-coupled receptor 183 (GPR183), also known as Epstein-Barr virus-induced gene 2 (EBI2), is an oxysterol-activated chemotactic receptor that regulates migration of B cells. We investigated the role of GPR183 in B1 cells in the peritoneal cavity and omentum. B1 cells expressed GPR183 at the mRNA level and migrated towards the GPR183 ligand 7α,25-dihydroxycholesterol (7α,25-OHC). GPR183 knock-out (KO) mice had smaller omenta, but with normal numbers of B1 cells, whereas they had fewer B2 cells in the omentum and peritoneal cavity than wildtype (WT) mice. GPR183 was not responsible for B1 cell accumulation in the omentum in response to i.p. lipopolysaccharide (LPS)-injection, in spite of a massive increase in 7α,25-OHC levels. Lack of GPR183 also did not affect B1a- or B1b cell-specific antibody responses after vaccination. In conclusion, we found that GPR183 is non-essential for the accumulation and function of B1 cells in the omentum and peritoneal cavity, but that it influences the abundance of B2 cells in these compartments.

Neonatal Exposure to Commensal-Bacteria-Derived Antigens Directs Polysaccharide-Specific B-1 B Cell Repertoire Development

B-1 B cells derive from a developmental program distinct from that of conventional B cells, through B cell receptor (BCR)-dependent positive selection of fetally derived precursors. Here, we used direct labeling of B cells reactive with the N-acetyl-D-glucosamine (GlcNAc)-containing Lancefield group A carbohydrate of Streptococcus pyogenes to study the effects of bacterial antigens on the emergent B-1 B cell clonal repertoire. The number, phenotype, and BCR clonotypes of GlcNAc-reactive B-1 B cells were modulated by neonatal exposure to heat-killed S. pyogenes bacteria. GlcNAc-reactive B-1 clonotypes and serum antibodies were reduced in germ-free mice compared with conventionally raised mice. Colonization of germ-free mice with a conventional microbiota promoted GlcNAc-reactive B-1 B cell development and concomitantly elicited clonally related IgA⁺ plasma cells in the small intestine. Thus, exposure to microbial antigens in early life determines the clonality of the mature B-1 B cell repertoire and ensuing antibody responses, with implications for vaccination approaches and schedules.

Differentiation of antibody-secreting cells in the thymus of human neonates

Thymic resident B cells were reported for the first time more than 40 years ago. Yet, their phenotype and significance remain unclear. In this study, we investigated the heterogeneity of thymic B cells in neonates as an indication of their possible function. Using thymuses from 21 neonates, we observed two consistent subsets, CD19+CD21+CD35+ and CD19+CD21−CD35−, accounting for virtually all thymic B cells. ELISPOT assays revealed the presence of IgG, IgA, IgM and even IgE antibody-secreting cells within the CD21−CD35− subset but not the CD21+CD35+ subset. To characterize the heterogeneity of CD21−CD35− subset, we used a single-cell RNA-sequencing and identified 4 separate clusters, 3 of which included cells with a phenotype and transcriptome consistent with that of B cell activation and proliferation. The more distant cluster corresponded to plasma cells (PCs) expressing IGHG, IGHA, and IGHE, implying prior class-switch recombination. To assess their specificity, we generated recombinant monoclonal antibodies (rAbs) from 362 PCs using a paired IgH and lgL chain expression cloning strategy. For comparison, rAbs were also generated from 296 undifferentiated CD21+CD35+ thymic B cells. The PC contingent was highly enriched in clones reactive to apoptotic cells when compared to CD21+CD35+ naïve B cells, an essential characteristic of natural antibodies. Remarkably, we identified individual PC clones reactive to some bacterial species also recognized by natural antibodies. Taken together, we demonstrate the differentiation of plasma cells reactive to apoptotic cells and common bacteria within the thymus, suggesting that thymus is a source of natural antibodies, contributing to newborn humoral immunity.

Neonatal exposure to commensal bacteria-derived antigens directs polysaccharide-specific B-1 B cell repertoire development

Mouse B-1 B lymphocytes play essential roles in defense against infectious microorganisms and maintenance of self-tolerance by producing natural antibodies. However, whether exogenous factors influence B-1 B cell repertoire formation remains poorly understood. Herein, we demonstrate that early immunization with N-acetyl-D-glucosamine (GlcNAc)-bearing Streptococcus pyogenes elicits GlcNAc-reactive B-1 B cells in C57BL/6 mice expressing immunoglobulin heavy chains distinct from those of naïve mice and mice immunized with S. pyogenes in adulthood. Moreover, germ-free mice exhibit greatly reduced GlcNAc-reactive serum antibodies and deficiencies in oligoclonal GlcNAc-reactive B-1 cell clonotypes dominant in conventionally raised mice. These phenotypes are also observed in Myd88-deficient mice and reversed following conventionalization of adult germ-free mice. We show that colonization by the microbiota promotes development of GlcNAc-reactive B cells and IgA-secreting plasma cells in the small intestine that are clonally related to PerC and splenic B-1 B cells. These results indicate that environmental and microbiota-derived antigens influence B-1 clonotype selection into the mature repertoire.

Glycan Reactive Natural Antibodies and Viral Immunity

Adaptive antibody responses provide a crucial means of host defense against viral infections by mediating the neutralization and killing infectious pathogens. At the forefront of humoral defense against viruses lie a subset of innate-like serum antibodies known as natural antibodies (NAbs). NAbs serve multifaceted functions in host defense and play an essential role in early immune responses against viruses. However, there remain many unanswered questions with regard to both the breadth of viral antigens recognized by NAbs, and how B cell ontology and individual antigenic histories intersect to control the development and function of antiviral human NAbs. In the following article we briefly review the current understanding of the functions and source of NAbs in the immune repertoire, their role during antiviral immune responses, the factors influencing the maturation of the NAb repertoire, and finally, the gaps and future research needed to advance our understanding of innate-like B cell biology for the purpose of harnessing NAbs for host defense against viral infections.

Genetic benefits of genomic selection breeding programmes considering foreign sire contributions

Background

In modern dairy breeding programmes, high contributions from foreign sires are nearly always present. Genotyping, and therefore genomic selection (GS), concern only a subpopulation of the breeding programme’s wider dairy population. These features of a breeding programme contribute in different ways to the rate of genetic gain for the wider industry.

Methods

A deterministic recursive gene flow model across subpopulations of animals in a dairy industry was created to predict the commercial performance of replacement heifers and future artificial insemination bulls. Various breeding strategies were assessed by varying the reliability of breeding values, the genetic contributions from subpopulations, and the genetic trend and merit of the foreign subpopulation.

Results

A higher response in the true breeding goal measured in standard deviations (SD) of true merit (G) after 20 years of selection can be achieved when genetic contributions shift towards higher merit alternatives compared to keeping them fixed. A foreign annual genetic trend of 0.08 SD of the breeding goal, while the domestic genetic trend is 0.10 SD, results in the overall net present value of genetic gain increasing by 1.2, 2.3, and 3.4% after 20 years as the reliability of GS in the domestic population increased from 0.3 to 0.45, 0.60 and 0.75. With a foreign genetic trend of 0.10 SD, these increases are more modest; 0.9, 1.7, and 2.4%. Increasing the foreign genetic trend so that it is higher than the domestic trend erodes the benefits of increasing the reliability of domestic GS further.

Conclusions

Having a foreign source of genetic material with a high rate of genetic progress contributes substantially to the benefits of domestic genetic progress while at the same time reducing the expected returns from investments to improve the accuracy of genomic prediction in the home country.

Chemical Synthesis and Application of Biotinylated Oligo-α-(1 → 3)-d-Glucosides To Study the Antibody and Cytokine Response against the Cell Wall α-(1 → 3)-d-Glucan of Aspergillus fumigatus

Biotinylated hepta-, nona- and undeca-α-(1 → 3)-d-glucosides representing long oligosaccharides of α-(1 → 3)-d-glucan, one of the major components of the cell walls of the fungal pathogen Aspergillus fumigatus, were synthesized for the first time via a blockwise strategy. Convergent assembly of the α-(1 → 3)-d-glucan chains was achieved by glycosylation with oligoglucoside derivatives bearing 6- O-benzoyl groups. Those groups are capable of remote α-stereocontrolling participation, making them efficient α-directing tools even in the case of large glycosyl donors. Synthetic biotinylated oligoglucosides (and biotinylated derivatives of previously synthesized tri- and penta-α-(1 → 3)-d-glucosides) loaded on streptavidin microtiter plates were shown to be better recognized by anti-α-(1 → 3)-glucan human polyclonal antibodies and to induce higher cytokine responses upon stimulation of human peripheral blood mononuclear cells than their natural counterpart, α-(1 → 3)-d-glucan, immobilized on a conventional microtiter plate. Attachment of the synthetic oligosaccharides equipped with a hydrophilic spacer via the streptavidin-biotin pair allows better spatial presentation and control of the loading compared to the random sorption of natural α-(1 → 3)-glucan. Increase of oligoglucoside length results in their better recognition and enhancement of cytokine production. Thus, using synthetic α-(1 → 3)-glucan oligosaccharides, we developed an assay for the host immune response that is more sensitive than the assay based on native α-(1 → 3)-glucan.

IL-7 Enables Antibody Responses to Bacterial Polysaccharides by Promoting B Cell Receptor Diversity

Polysaccharide vaccines such as the Vi polysaccharide (ViPS) of Salmonella enterica serovar Typhi induce efficient Ab responses in adults but not in young children. The reasons for this difference are not understood. IL-7 dependency in B cell development increases progressively with age. IL-7Rα-mediated signals are required for the expression of many VH gene segments that are distal to DH-JH in the IgH locus and for the complete diversification of the BCR repertoire. Therefore, we hypothesized that B cells generated in the absence of IL-7 do not recognize a wide range of Ags because of a restricted BCR repertoire. Compared with adult wildtype mice, young wildtype mice and IL-7-deficient adult mice generated a significantly reduced Ab response to ViPS. Additionally, ViPS-binding B cells in adult wildtype mice predominantly used distal VH gene segments. Transgenic expression of either IL-7 or a BCR encoded by a distal VH gene segment permitted young mice to respond efficiently to bacterial polysaccharides. These results indicate that restricted VH gene usage early in life results in a paucity of Ag-specific B cell precursors, thus limiting antipolysaccharide responses.

Myeloid-Derived Suppressor Cells Impair B Cell Responses in Lung Cancer through IL-7 and STAT5

Myeloid-derived suppressor cells (MDSCs) are known suppressors of antitumor immunity, affecting amino acid metabolism and T cell function in the tumor microenvironment. However, it is unknown whether MDSCs regulate B cell responses during tumor progression. Using a syngeneic mouse model of lung cancer, we show reduction in percentages and absolute numbers of B cell subsets including pro-, pre-, and mature B cells in the bone marrow (BM) of tumor-bearing mice. The kinetics of this impaired B cell response correlated with the progressive infiltration of MDSCs. We identified that IL-7 and downstream STAT5 signaling that play a critical role in B cell development and differentiation were also impaired during tumor progression. Global impairment of B cell function was indicated by reduced serum IgG levels. Importantly, we show that anti-Gr-1 Ab-mediated depletion of MDSCs not only rescued serum IgG and IL-7 levels but also reduced TGF-β1, a known regulator of stromal IL-7, suggesting MDSC-mediated regulation of B cell responses. Furthermore, blockade of IL-7 resulted in reduced phosphorylation of downstream STAT5 and B cell differentiation in tumor-bearing mice and administration of TGF-β-blocking Ab rescued these IL-7-dependent B cell responses. Adoptive transfer of BM-derived MDSCs from tumor-bearing mice into congenic recipients resulted in significant reductions of B cell subsets in the BM and in circulation. MDSCs also suppressed B cell proliferation in vitro in an arginase-dependent manner that required cell-to-cell contact. Our results indicate that tumor-infiltrating MDSCs may suppress humoral immune responses and promote tumor escape from immune surveillance.

Platelet activating factor as a novel danger signal for activation of NLRP3 inflammasome

Platelet activating factor (PAF) is a biologically active phospholipid that promotes pathophysiological inflammation through binding to a unique G-protein-coupled seven transmembrane receptor (PAFR). Increased PAF level has been correlated with a number of inflammatory disorders, yet the molecular mechanism underlying the pro-inflammatory function of PAF remains incompletely elucidated. Here we showed PAF activates canonical NLRP3 inflammasome, resulting in ASC oligomerization, caspase-1 processing, and IL-1β and IL-18 maturation. PAF-induced IL-1β maturation is abrogated in macrophage from Nlrp3−/−, Asc−/−, Caspase-1−/− mice, but not Nlrc4−/−, Nlrp1−/−, Aim2−/−, Caspase-11−/− mice. In addition, NEK7, a new component of the NLRP3 inflammasome, is also essential for PAF induced IL-1β maturation. PAF activation of the NLRP3 inflammasome is dependent on calcium influx, potassium efflux, but independent of lysosome cathepsin, mitochondrial reactive oxygen species (ROS), and necroptosis. Surprisingly, PAFR is not essential for PAF induced NLRP3 inflammasome activation. Physiologically, PAF induced shock is protected in NLRP3 inflammasome component deficient mice. Together, our findings reveal a new PAFR independent pathway for detecting PAF which represents an unprecedented danger signaling function of PAF, and provide new insight for understanding the pathogenesis of PAF-mediated inflammatory disorders.

SNP Data Quality Control in a National Beef and Dairy Cattle System and Highly Accurate SNP Based Parentage Verification and Identification

A major use of genetic data is parentage verification and identification as inaccurate pedigrees negatively affect genetic gain. Since 2012 the international standard for single nucleotide polymorphism (SNP) verification in Bos taurus cattle has been the ISAG SNP panels. While these ISAG panels provide an increased level of parentage accuracy over microsatellite markers (MS), they can validate the wrong parent at ≤1% misconcordance rate levels, indicating that more SNP are needed if a more accurate pedigree is required. With rapidly increasing numbers of cattle being genotyped in Ireland that represent 61 B. taurus breeds from a wide range of farm types: beef/dairy, AI/pedigree/commercial, purebred/crossbred, and large to small herd size the Irish Cattle Breeding Federation (ICBF) analyzed different SNP densities to determine that at a minimum ≥500 SNP are needed to consistently predict only one set of parents at a ≤1% misconcordance rate. For parentage validation and prediction ICBF uses 800 SNP (ICBF800) selected based on SNP clustering quality, ISAG200 inclusion, call rate (CR), and minor allele frequency (MAF) in the Irish cattle population. Large datasets require sample and SNP quality control (QC). Most publications only deal with SNP QC via CR, MAF, parent-progeny conflicts, and Hardy-Weinberg deviation, but not sample QC. We report here parentage, SNP QC, and a genomic sample QC pipelines to deal with the unique challenges of >1 million genotypes from a national herd such as SNP genotype errors from mis-tagging of animals, lab errors, farm errors, and multiple other issues that can arise. We divide the pipeline into two parts: a Genotype QC and an Animal QC pipeline. The Genotype QC identifies samples with low call rate, missing or mixed genotype classes (no BB genotype or ABTG alleles present), and low genotype frequencies. The Animal QC handles situations where the genotype might not belong to the listed individual by identifying: >1 non-matching genotypes per animal, SNP duplicates, sex and breed prediction mismatches, parentage and progeny validation results, and other situations. The Animal QC pipeline make use of ICBF800 SNP set where appropriate to identify errors in a computationally efficient yet still highly accurate method.

Genomic Characterisation of the Indigenous Irish Kerry Cattle Breed

Kerry cattle are an endangered landrace heritage breed of cultural importance to Ireland. In the present study we have used genome-wide SNP array data to evaluate genomic diversity within the Kerry population and between Kerry cattle and other European breeds. Patterns of genetic differentiation and gene flow among breeds using phylogenetic trees with ancestry graphs highlighted historical gene flow from the British Shorthorn breed into the ancestral population of modern Kerry cattle. Principal component analysis (PCA) and genetic clustering emphasised the genetic distinctiveness of Kerry cattle relative to comparator British and European cattle breeds. Modelling of genetic effective population size (N_e) revealed a demographic trend of diminishing N_e over time and that recent estimated N_e values for the Kerry breed may be less than the threshold for sustainable genetic conservation. In addition, analysis of genome-wide autozygosity (F_ROH) showed that genomic inbreeding has increased significantly during the 20 years between 1992 and 2012. Finally, signatures of selection revealed genomic regions subject to natural and artificial selection as Kerry cattle adapted to the climate, physical geography and agro-ecology of southwest Ireland.

Accelerated Systemic Autoimmunity in the Absence of Somatic Hypermutation in 564Igi: A Mouse Model of Systemic Lupus with Knocked-In Heavy and Light Chain Genes

564Igi mice have knocked-in immunoglobulin (Ig) heavy (H) and light (L) chain genes that encode an autoantibody recognizing RNA. Previously, we showed that these mice produce pathogenic IgG autoantibodies when activation-induced deaminase (AID) is expressed in pre-B and immature B cells but not when it is expressed only in mature B cells. AID has two functions; it is necessary for somatic hypermutation (SHM) and class switch recombination (CSR). To determine the role of each of these functions in the generation of pathogenic autoantibodies, we generated 564Igi mice that carry a mutant AID-encoding gene, Aicda (Aicda^G23S), which is capable of promoting CSR but not SHM. We found that 564Igi Aicda^G23S mice secreted class-switched antibodies (Abs) at levels approximately equal to 564Igi mice. However, compared to 564Igi mice, 564Igi Aicda^G23S mice had increased pathogenic IgG Abs and severe systemic lupus erythematosus-like disease, including, glomerulonephritis, and early death. We suggest that in 564Igi mice SHM by AID changes Ig receptors away from self reactivity, thereby mitigating the production of autoantibody, providing a novel mechanism of tolerance.

Irgm1 coordinately regulates autoimmunity and host defense at select mucosal surfaces

The pathogenesis of primary Sjogren's syndrome (SS), an autoimmune disease that targets the mucosa of exocrine tissues, is poorly understood. Although several mouse models have been developed that display features of SS, most of these are within the larger context of a lupus-like presentation. Immunity-related GTPase family M protein 1 (Irgm1) is an interferon-inducible cytoplasmic GTPase that is reported to regulate autophagy and mitochondrial homeostasis. Here, we report that naive Irgm1-/- mice display lymphocytic infiltration of multiple mucosal tissues including the lung in a manner reminiscent of SS, together with IgA class-predominant autoantibodies including anti-Ro and anti-La. This phenotype persists in the germ-free state, but is abolished by deletion of Irgm3. Irgm1-/- mice have increased local production in the lung of TECP15-idiotype IgA, a natural antibody with dual reactivity against host and pneumococcal phosphorylcholine. Associated with this, Irgm1-/- mice display enhanced opsonization and clearance of Streptococcus pneumoniae from the lung and increased survival from pneumococcal pneumonia. Taken together, our results identify Irgm1 as a master regulator of mucosal immunity that dually modulates evolutionarily conserved self- and other-directed immune responses at the interface of host with environment.

CD36 and Platelet-Activating Factor Receptor Promote House Dust Mite Allergy Development

Over 89% of asthmatic children in underdeveloped countries demonstrate sensitivity to house dust mites (HDMs). The allergic response to HDMs is partially mediated by epithelial cell-derived cytokines that activate group 2 innate lymphoid cells, induce migration and activation of dendritic cells, and promote effector differentiation of HDM-specific TH2 cells. However, the contribution of innate receptor engagement on epithelial or dendritic cells by HDMs that ultimately mediates said innate and adaptive allergic responses is poorly understood. We and other investigators have demonstrated that HDMs express phosphorylcholine (PC) moieties. The major PC receptors involved in immune responses include CD36 and platelet-activating factor receptor (PAFR). Because CD36 and PAFR are expressed by epithelial cells and dendritic cells, and expression of these receptors is higher in human asthmatics, we determined whether engagement of CD36 or PAFR on epithelial or dendritic cells contributes to HDM allergy development. Testing bone marrow chimeric mice revealed that CD36 engagement on radioresistant cells and PAFR engagement on radioresistant and radiosensitive cells in the lung promote allergic responses to HDMs. Additionally, passive anti-PC IgM Abs administered intratracheally with HDMs decreased allergen uptake by epithelial cells and APCs in the lungs of C57BL/6 mice but not CD36^-/- or PAFR^-/- mice. These results show that CD36 and PAFR are important mediators of HDM allergy development and that inhibiting HDM engagement with PC receptors in the lung protects against allergic airway disease.

Transitional B cells commit to marginal zone B cell fate by Taok3-mediated surface expression of ADAM10

Notch2 and B cell antigen receptor (BCR) signaling determine whether transitional B cells become marginal zone B (MZB) or follicular B (FoB) cells in the spleen, but it is unknown how these pathways are related. We generated Taok3^-/- mice, lacking the serine/threonine kinase Taok3, and found cell-intrinsic defects in the development of MZB but not FoB cells. Type 1 transitional (T1) B cells required Taok3 to rapidly respond to ligation by the Notch ligand Delta-like 1. BCR ligation by endogenous or exogenous ligands induced the surface expression of the metalloproteinase ADAM10 on T1 B cells in a Taok3-dependent manner. T1 B cells expressing surface ADAM10 were committed to becoming MZB cells in vivo, whereas T1 B cells lacking expression of ADAM10 were not. Thus, during positive selection in the spleen, BCR signaling causes immature T1 B cells to become receptive to Notch ligands via Taok3-mediated surface expression of ADAM10.

Evaluation of developed low-density genotype panels for imputation to higher density in independent dairy and beef cattle populations

The objective of this study was to develop, using alternative algorithms, low-density SNP genotyping panels (384 to 12,000 SNP), which can be accurately imputed to higher-density panels across independent cattle populations. Single nucleotide polymorphisms were selected based on genomic characteristics (i.e., linkage disequilibrium [LD], minor allele frequency [MAF], and genomic distance) in a population of 1,267 Holstein-Friesian animals genotyped on the Illumina Bovine50 Beadchip (54,001 SNP). Single nucleotide polymorphism selection methods included 1) random; 2) equidistant location; 3) combination of SNP MAF and LD structure while maintaining relatively equal genomic distance between adjacent SNP; 4) a combination of high MAF, genomic distance between selected and candidate SNP, and correlation between genotypes of selected and candidate SNP; and 5) a machine learning algorithm. The panels were validated separately in 1) a population of 750 Holstein-Friesian animals with masked genotypes to reflect the lower-density SNP densities under investigation (1,249 animals with complete genotypes included in reference population) and 2) a population of 359 Limousin and Charolais cattle with high (777,962 SNP)-density genotypes (1,918 animals with complete genotypes included in the reference population). Irrespective of SNP selection method, imputation accuracy in both populations improved at a diminishing rate as the number of SNP included in the lower-density genotype panel increased. Additionally, the variability in mean imputation accuracy per individual decreased as the panel density increased. The SNP selection method had a major impact on the mean allele concordance rate, although its impact diminished as the panel density increased. Imputation accuracy for SNP selected using a combination of high SNP MAF, LD structure, and relatively equal genomic distance between SNP outperformed all other selection methods in densities < 12,000 SNP. Using this method of SNP selection, the correlation between the imputed and actual genotypes for the 3,000 SNP panel was 0.90 and 0.96 when applied to the beef and dairy populations, respectively; the respective correlations for the 6,000 SNP panel were 0.95 and 0.98. It is necessary to include between 3,000 and 6,000 SNP in a low-density panel to achieve adequate imputation accuracy to either medium density (approximately 50,000 SNP in the dairy population) or high density (approximately 700,000 SNP in the beef population) across diverse and independent populations.

Immunological Outcomes of Antibody Binding to Glycans Shared between Microorganisms and Mammals

Glycans constitute basic cellular components of living organisms across biological kingdoms, and glycan-binding Abs participate in many cellular interactions during immune defense against pathogenic organisms. Glycan epitopes are expressed as carbohydrate-only entities or as oligomers or polymers on proteins and lipids. Such epitopes on glycoproteins may be formed by posttranslational modifications or neoepitopes resulting from metabolic-catabolic processes and can be altered during inflammation. Pathogenic organisms can display host-like glycans to evade the host immune response. However, Abs to glycans, shared between microorganisms and the host, exist naturally. These Abs are able to not only protect against infectious disease, but also are involved in host housekeeping functions and can suppress allergic disease. Despite the reactivity of these Abs to glycans shared between microorganisms and host, diverse tolerance-inducing mechanisms permit the B cell precursors of these Ab-secreting cells to exist within the normal B cell repertoire.

Manipulation of the glycan-specific natural antibody repertoire for immunotherapy

Natural immunoglobulin derived from innate-like B lymphocytes plays important roles in the suppression of inflammatory responses and represents a promising therapeutic target in a growing number of allergic and autoimmune diseases. These antibodies are commonly autoreactive and incorporate evolutionarily conserved specificities, including certain glycan-specific antibodies. Despite this conservation, exposure to bacterial polysaccharides during innate-like B lymphocyte development, through either natural exposure or immunization, induces significant changes in clonal representation within the glycan-reactive B cell pool. Glycan-reactive natural antibodies (NAbs) have been reported to play protective and pathogenic roles in autoimmune and inflammatory diseases. An understanding of the composition and functions of a healthy glycan-reactive NAb repertoire is therefore paramount. A more thorough understanding of NAb repertoire development holds promise for the design of both biological diagnostics and therapies. In this article, we review the development and functions of NAbs and examine three glycan specificities, represented in the innate-like B cell pool, to illustrate the complex roles environmental antigens play in NAb repertoire development. We also discuss the implications of increased clonal plasticity of the innate-like B cell repertoire during neonatal and perinatal periods, and the prospect of targeting B cell development with interventional therapies and correct defects in this important arm of the adaptive immune system.

Pulmonary α-1,3-Glucan-Specific IgA-Secreting B Cells Suppress the Development of Cockroach Allergy

There is a higher incidence of allergic conditions among children living in industrialized countries than those in developing regions. One explanation for this is reduced neonatal exposure to microbes and the consequent lack of immune stimulation. Sensitivity to cockroach allergen is highly correlated with the development of severe asthma. In this study, we determined that an Ab to microbial α-1,3-glucan binds an Enterobacter species and cockroach allergen. Neonatal, but not adult, mice immunized with this α-1,3-glucan-bearing Enterobacter (MK7) are protected against cockroach allergy. Following exposure to cockroach allergen, α-1,3-glucan-specific IgA-secreting cells are present in the lungs of mice immunized with MK7 as neonates but not in the lungs of those immunized as adults. Mice that are unable to generate anti-α-1,3-glucan IgA Abs were immunized with MK7 as neonates and were no longer protected against cockroach allergy. Thus, neonatal, but not adult, exposure to α-1,3-glucan results in suppressed development of cockroach allergy via pulmonary α-1,3-glucan-specific IgA-secreting cells.

Pulmonary anti-α-1,3-glucan IgA-secreting B cells are protective against cockroach-induced allergic disease

Currently, an estimated 20% of the population worldwide suffers from an allergic disorder. Children born in industrialized countries have a higher risk of acquiring allergies and asthma than those in developing countries. This difference has been attributed to lower exposure to microbial antigens during early life and the consequent lack of stimulation for the developing immune system. We have previously demonstrated that bacteria and allergens can bear similar epitopes. German cockroach allergen and an enteric Enterobacter species isolated from mice bear similarly-recognized α-1,3-glucan epitopes. Neonatal mice have a large frequency of anti-α-1,3-glucan-IgA secreting cells that significantly decrease by 5 weeks of age. Following challenge with cockroach allergen, neonatal, but not adult, mice immunized with α-1,3-glucan-bearing Enterobacter had a significantly decreased frequency of eosinophils and T cells in the pulmonary parenchyma, antigen-specific memory T cells in the mediastinal lymph node, and IgE in the blood compared to mice immunized with α-1,3-glucan-deficient Enterobacter. A unique population of anti-α-1,3-glucan IgA-secreting cells were identified in the lungs of mice immunized with α-1,3-glucan-bearing Enterobacter as neonates, but not in those immunized as adults. IgA-deficient mice immunized with α-1,3-glucan-bearing Enterobacter as neonates were no longer protected against allergic disease development. We suggest that early immunization with α-1,3-glucan selects neonatal anti-α-1,3-glucan-IgA secreting clones for incorporation in to the adult repertoire such that these B cells have the ability to suppress the development of cockroach-induced allergic disease during adult life.

Effects of neonatal antigen exposure on natural antibody repertoire development

B-1 B cells produce natural antibodies that contribute significantly to maintenance of immunological homeostasis, however the role exogenous antigens play in the development of the B-1 B cell repertoire is unclear. N-acetyl-D-glucosamine (GlcNAc)-reactive antibodies are universally represented in mammals, and some GlcNAc-reactive B cell clonotypes are autoreactive due to the conservation of orthologous GlcNAc epitopes in mammals and microorganisms. We report here that neonatal immunization with GlcNAc-bearing Group A Streptococcus significantly expands CD5-bearing GlcNAc-reactive B-1 B cell populations, alters the GlcNAc- reactive clonal repertoire, and suppresses class-switch antibody responses upon secondary immunization in adulthood. We further find that in the absence of exogenous antigen stimulation, germ-free mice exhibit log-reductions in the number of GlcNAc-reactive B-1 B cells and the levels of circulating antibodies. Importantly, clonal analyses of B cells from germ-free mice reveals a lack of GlcNAc-reactive innate-like B cell clonotypes that are highly conserved between mice raised under SPF conditions. Collectively, these data indicate that exposure to exogenous antigen during perinatal development can directly influence clonal representation within certain B-1 B cell specificities. These observations suggest that integration of signals derived from exogenous antigen is required for the development of certain clonal specificities that are negatively selected in the absence of exogenous stimuli. Given the functions of natural antibodies, these observations may hold major implications for the roles of environmental factors in the development of autoimmune disease.

B cell autophagy mediates TLR7-dependent autoimmunity and inflammation

Systemic lupus erythematosus (SLE) is a heterogeneous autoimmune disease, defined by loss of B cell self-tolerance that results in production of antinuclear antibodies (ANA) and chronic inflammation. While the initiating events in lupus development are not well defined, overexpression of the RNA-recognizing toll-like receptor (TLR)7 has been linked to SLE in humans and mice. We postulated that autophagy plays an essential role in TLR7 activation of B cells for the induction of SLE by delivering RNA ligands to the endosomes, where this innate immune receptor resides. To test this hypothesis, we compared SLE development in Tlr7 transgenic (Tg) mice with or without B cell-specific ablation of autophagy (Cd19-Cre Atg5(f/f)). We observed that in the absence of B cell autophagy the 2 hallmarks of SLE, ANA and inflammation, were eliminated, thus curing these mice of lupus. This was also evident in the significantly extended survival of the autophagy-deficient mice compared to Tlr7.1 Tg mice. Furthermore, glomerulonephritis was ameliorated, and the serum levels of inflammatory cytokines in the knockout (KO) mice were indistinguishable from those of control mice. These data provide direct evidence that B cells require TLR7-dependent priming through an autophagy-dependent mechanism before autoimmunity is induced, thereafter involving many cell types. Surprisingly, hyper-IgM production persisted in Tlr7.1 Tg mice in the absence of autophagy, likely involving a different activation pathway than the production of autoantibodies. Furthermore, these mice still presented with anemia, but responded with a striking increase in extramedullary hematopoiesis (EMH), possibly due to the absence of pro-inflammatory cytokines.

Neonatal exposure to pneumococcal phosphorylcholine modulates the development of house dust mite allergy during adult life

Currently, ∼20% of the global population suffers from an allergic disorder. Allergies and asthma occur at higher rates in developed and industrialized countries. It is clear that many human atopic diseases are initiated neonatally and herald more severe IgE-mediated disorders, including allergic asthma, which is driven by the priming of Th2 effector T cells. The hygiene hypothesis attempts to link the increased excessively sanitary conditions early in life to a default Th2 response and increasing allergic phenomena. Despite the substantial involvement of IgE Abs in such conditions, little attention has been paid to the effects of early microbial exposure on the B cell repertoire prior to the initiation of these diseases. In this study, we use Ab-binding assays to demonstrate that Streptococcus pneumoniae and house dust mite (HDM) bear similar phosphorylcholine (PC) epitopes. Neonatal C57BL/6 mice immunized with a PC-bearing pneumococcal vaccine expressed increased frequencies of PC-specific B cells in the lungs following sensitizing exposure to HDM as adults. Anti-PC IgM Abs in the lung decreased the interaction of HDM with pulmonary APCs and were affiliated with lowered allergy-associated cell infiltration into the lung, IgE production, development of airway hyperresponsiveness, and Th2 T cell priming. Thus, exposure of neonatal mice to PC-bearing pneumococci significantly reduced the development of HDM-induced allergic disease during adult life. Our findings demonstrate that B cells generated against conserved epitopes expressed by bacteria, encountered early in life, are also protective against the development of allergic disease during adult life.

Antibodies generated against Streptococci protect in a mouse model of disseminated aspergillosis

Invasive aspergillosis (IA) resulting from infection by Aspergillus fumigatus is a leading cause of death in immunosuppressed populations. There are limited therapeutic options for this disease and currently no vaccine. There is evidence that some anti-A. fumigatus mAbs can provide protection against IA. However, vaccine development has been impeded by a paucity of immunological targets on this organism demonstrated to provide protective responses. Sialylated oligosaccharide epitopes found on a variety of pathogens, including fungi and group B streptococci (GBS), are thought to be major virulence factors of these organisms facilitating pathogen attachment to host cells and modulating complement activation and phagocytosis. Because some of these oligosaccharide structures are conserved across kingdoms, we screened a panel of mAbs raised against GBS serotypes for reactivity to A. fumigatus. This approach revealed that SMB19, a GBSIb type-specific mAb, reacts with A. fumigatus conidia and hyphae. The presence of this Ab in mice, as a result of passive or active immunization, or by enforced expression of the SMB19 H chain as a transgene, results in significant protection in both i.v. and airway-induced models of IA. This study demonstrates that some Abs generated against bacterial polysaccharides engage fungal pathogens and promote their clearance in vivo and thus provide rationale of alternative strategies for the development of vaccines or therapeutic mAbs against these organisms.

Natural antibody repertoires: development and functional role in inhibiting allergic airway disease

In this review we discuss the effects of microbial exposure on the B cell repertoire. Neonatal exposure to conserved bacterial carbohydrates and phospholipids permanently reprograms the natural antibody repertoire directed toward these antigens by clonal expansion, alterations in clonal dominance, and increased serum antibody levels. These epitopes are present not only in bacterial cell walls, but also in common environmental allergens. Neonatal immunization with bacterial polysaccharide vaccines results in attenuated allergic airway responses to fungi-, house dust mite-, and cockroach-associated allergens in mouse models. The similarities between mouse and human natural antibody repertoires suggest that reduced microbial exposure in children may have the opposite effect, providing a potential mechanistic explanation for the hygiene hypothesis. We propose that understanding the effects of childhood infections on the natural antibody repertoire and the mechanisms of antibody-mediated immunoregulation observed in allergy models will lead to the development of prevention/interventional strategies for treatment of allergic asthma.

Unique ligand-binding property of the human IgM Fc receptor

The IgM Fc receptor (FcμR) is the newest FcR, and coligation of FcμR and Fas/CD95 on Jurkat cells with agonistic IgM anti-Fas mAb was shown to inhibit Fas-induced apoptosis. The ligand-binding activity of human FcμR was further examined. FcμR-mediated protection from apoptosis was partially blocked by addition of 10(4) molar excess of IgM or its soluble immune complexes, but it could be inhibited by addition of 10-fold excess of IgM anti-CD2 mAb. This suggests that FcμR binds more efficiently to the Fc portion of IgM reactive with plasma-membrane proteins than to the Fc portion of IgM in solution. The former interaction occurred in cis on the same cell surface, but not in trans between neighboring cells. This cis engagement of FcμR resulted in modulation of Ca(2+) mobilization via CD2 on Jurkat cells or BCRs on blood B cells upon cross-linkage with the corresponding IgM mAbs. Several functional changes were observed with FcμR mutants: 1) significant increase in IgM ligand binding in the cytoplasmic tail-deletion mutant, 2) enhanced cap formation in FcμR upon IgM binding at 4°C with a point mutation of the transmembrane His to Phe, and 3) less protective activity of FcμR in IgM anti-Fas mAb-mediated apoptosis assays with a point mutation of the membrane-proximal Tyr to Phe. These findings show the importance of the cis engagement of FcμR and its critical role in receptor function. Hence, FcμR on B, T, and NK cells may modulate the function of surface proteins recognized by natural or immune IgM Abs on the shared membrane cell surface.

Dosage of X-linked Toll-like receptor 8 determines gender differences in the development of systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease with a high incidence in females and a complex phenotype. Using 564Igi mice, a model of SLE with knock-in genes encoding an autoreactive anti-RNA Ab, we investigated how expression of Toll-like receptors (TLRs) in B cells and neutrophils affects pathogenesis. We established that TLR signaling through MyD88 is necessary for disease. Autoantibody was produced in mice with single deletions of Tlr7, Tlr8, or Tlr9 or combined deletions of Tlr7 and Tlr9. Autoantibody was not produced in the combined absence of Tlr7 and Tlr8, indicating that TLR8 contributes to the break in tolerance. Furthermore, TLR8 was sufficient for the loss of B-cell tolerance, the production of class-switched autoantibody, heightened granulopoiesis, and increased production of type I IFN by neutrophils as well as glomerulonephritis and death. We show that dosage of X-linked Tlr8 plays a major role in the high incidence of disease in females. In addition, we show that the negative regulation of disease by TLR9 is exerted primarily on granulopoiesis and type I IFN production by neutrophils. Collectively, we suggest that individual TLRs play unique roles in the pathogenesis of systemic lupus erythematosus, suggesting new targets for treatment.

The link between antibodies to OxLDL and natural protection against pneumococci depends on D(H) gene conservation

Germline D_H sequences are required for the generation of natural antibodies reactive to bacterial phosphorylcholine but not for those reactive to self-antigen.

Selection and physiological production of protective natural antibodies (NAbs) have been associated with exposure to endogenous antigens. The extent to which this association depends on germline NAb sequence is uncertain. Here we show that alterations in germline D_H sequence can sever the association between the production of self-reactive NAbs and NAbs that afford protection against a pathogen. In unmanipulated hosts, the availability of the evolutionarily conserved DFL16.1 gene segment sequence profoundly affected the serum levels of NAbs against bacterial phosphorylcholine but not oxidized low-density lipoprotein. Mice with partially altered DFL16.1 sequence could use N nucleotides to recreate the amino acid sequence associated with the classical protective T15 idiotype–positive NAbs, whereas those without DFL16.1 could not. DFL16.1 gene–deficient mice proved more susceptible to challenge with live Streptococcus pneumoniae. Our findings indicate that although production of self-reactive NAbs can be independent of germline D_H sequence, their capacity to provide protection against pathogens cannot. The potential relevance of these findings for the rational design of vaccines is discussed.

Antibodies generated against conserved antigens expressed by bacteria and allergen-bearing fungi suppress airway disease

There has been a sharp rise in allergic asthma and asthma-related deaths in the developed world, in contrast to many childhood illnesses that have been reduced or eliminated. The hygiene hypothesis proposes that excessively sanitary conditions early in life result in autoimmune and allergic phenomena because of a failure of the immune system to receive proper microbial stimulation during development. We demonstrate that Abs generated against conserved bacterial polysaccharides are reactive with and dampen the immune response against chitin and Aspergillus fumigatus. A reduction in Ag uptake, cell influx, cell activation, and cytokine production occurred in the presence of anti-polysaccharide Abs, resulting in a striking decrease in the severity of allergic airway disease in mice. Overall, our results suggest that Ag exposure--derived from environmental sources, self-antigens, or vaccination--during the neonatal period has dramatic effects on the adult Ab response and modifies the development of allergic airway disease.

Long-term maintenance of polysaccharide-specific antibodies by IgM-secreting cells

Many bacteria-associated polysaccharides induce long-lived Ab responses that protect against pathogenic microorganisms. The maintenance of polysaccharide-specific Ab titers may be due to long-lived plasma cells or ongoing Ag-driven B cell activation due to polysaccharide persistence. BALB/c and V(H)J558.3 transgenic mice respond to α1→3-dextran (DEX) by generating a peak anti-DEX response at 7 d, followed by maintenance of serum Ab levels for up to 150 d. Analysis of the cellular response to DEX identified a population of short-lived, cyclophosphamide-sensitive DEX-specific plasmablasts in the spleen, and a quiescent, cyclophosphamide-resistant DEX-specific Ab-secreting population in the bone marrow. BrdU pulse-chase experiments demonstrated the longevity of the DEX-specific Ab-secreting population in the bone marrow. Splenic DEX-specific plasmablasts were located in the red pulp with persisting DEX-associated CD11c(+) dendritic cells 90 d after immunization, whereas DEX was not detected in the bone marrow after 28 d. Selective depletion of short-lived DEX-specific plasmablasts and memory B1b B cells using cyclophosphamide and anti-CD20 treatment had a minimal impact on the maintenance of serum anti-DEX Abs. Collectively, these findings demonstrate that the maintenance of serum polysaccharide-specific Abs is the result of continuous Ag-driven formation of short-lived plasmablasts in the spleen and a quiescent population of Ab-secreting cells maintained in the bone marrow for a long duration.

Cathelin-related antimicrobial peptide differentially regulates T- and B-cell function

Mammalian antimicrobial peptides (AMPs) play an important role in host defense via direct antimicrobial activity as well as immune regulation. The mouse cathelin-related antimicrobial peptide (mCRAMP), produced from the mouse gene Camp, is the only mouse cathelicidin identified and the ortholog of the human gene encoding the peptide LL-37. This study tested the hypothesis that mouse B and T cells produce and respond to mCRAMP. We show that all mature mouse B-cell subsets, including follicular (FO), marginal zone (MZ), B1a, and B1b cells, as well as CD4(+) and CD8(+) T cells produce Camp mRNA and mCRAMP protein. Camp(-/-) B cells produced equivalent levels of IgM, IgG3, and IgG2c but less IgG1 and IgE, while Camp(-/-) CD4(+) T cells cultured in Th2-inducing conditions produced more IL-4-expressing cells when compared with WT cells, effects that were reversed upon addition of mCRAMP. In vivo, Camp(-/-) mice immunized with TNP-OVA absorbed in alum produced an enhanced TNP-specific IgG1 response when compared with WT mice. ELISpot analysis revealed increased numbers of TNP-specific IgG1-secreting splenic B cells and FACS analysis revealed increased CD4(+) T-cell IL-4 expression. Our results suggest that mCRAMP differentially regulates B- and T-cell function and implicate mCRAMP in the regulation of adaptive immune responses.

Limiting CDR-H3 diversity abrogates the antibody response to the bacterial polysaccharide α 1→3 dextran

Anti-polysaccharide Ab responses in mice are often oligoclonal, and the mechanisms involved in Ag-specific clone production and selection remain poorly understood. We evaluated the relative contribution of D(H) germline content versus N nucleotide addition in a classic oligoclonal, T-independent Ab response (α 1→3 dextran [DEX]) by challenging adult TdT-sufficient (TdT(+/+)) and TdT-deficient (TdT(-/-)) gene-targeted mice, limited to the use of a single D(H) gene segment (D-limited mice), with Enterobacter cloacae. D-limited mice achieved anti-DEX-specific levels of Abs that were broadly comparable to those of wild-type (WT) BALB/c mice. Sequence analysis of the third CDR of the H chain intervals obtained by PCR amplification of V(H) domain DNA from DEX-specific plasmablasts revealed the near universal presence of an aspartic acid residue (D99) at the V-D junction, irrespective of the composition of the D(H) locus. Although WT mice were able to use germline D(H) (DQ52, DSP, or DST) gene segment sequence, TdT activity, or both to produce D99, all three D-limited mouse strains relied exclusively on N addition. Additionally, in the absence of TdT, D-limited mice failed to produce a DEX response. Coupled with previous studies demonstrating a reduced response to DEX in TdT(-/-) mice with a WT D(H) locus, we concluded that in the case of the anti-DEX repertoire, which uses a short third CDR of the H chain, the anti-DEX response relies more intensely on sequences created by postnatal N nucleotide addition than on the germline sequence of the D(H).

Marginal zone B cells regulate antigen capture by marginal zone macrophages

The marginal zone (MZ) of the mouse spleen contains macrophages that express receptors that trap pathogens, including the scavenger receptor macrophage receptor with a collagenous structure and the C-type lectin specific intracellular adhesion molecule-grabbing nonintegrin receptor 1 (SIGN-R1). We previously reported that expression of SIGN-R1 was decreased in CD19-deficient mice. In this study, we demonstrate that SIGN-R1 is expressed on a subset of macrophage receptor with a collagenous structure (MARCO)(+) macrophages. This subset is diminished when MZ B cells are absent due to either genetic developmental defects or following transient migration of B cells out of the MZ. When B cells return to the MZ, there is a delay in recovery of SIGN-R1-expressing macrophages. During this period, capture of Ficoll, which for the macrophages requires SIGN-R1, remains defective not only by the macrophages, but also by the B cells. Thus, MZ B cells regulate expression of molecules on macrophages that are important for trapping Ag, which, in turn, is required for Ag capture by the B cells.

ExsB, an unusually highly phosphorylated protein required for the stable attachment of the exosporium of Bacillus anthracis

The outermost layer of the Bacillus anthracis spore, the exosporium, is composed of a paracrystalline basal layer and an external hair-like nap. The nap is formed from a single collagen-like glycoprotein, while the basal layer contains many different proteins, including a 186-amino acid protein called ExsB. In this study, we discovered that ExsB is unusually highly phosphorylated, with at least 14 of its 19 threonine residues modified. The phosphorylated threonines are included in seven contiguous approximately 12-residue imperfect repeats, which presumably contain kinase recognition sequences. We demonstrated that a B. anthracis DeltaexsB mutant unable to synthesize ExsB produced spores with an exosporium that was readily sloughed, indicating that ExsB was required for stable exosporium attachment. This unstable exosporium also lacked the enzyme alanine racemase, which is normally tightly associated with the exosporium. Additionally, purified DeltaexsB spores lacking a visible exosporium were devoid of most exosporium proteins but, surprisingly, retained the putative exosporium proteins BxpC and CotB-1. Finally, we showed that transcription of the exsB gene occurred only during the late stages of sporulation, and we used an active and phosphorylated ExsB-EGFP fusion protein to monitor ExsB localization to wild-type and DeltabxpB mutant exosporia.

Terminal deoxynucleotidyl transferase is required for an optimal response to the polysaccharide α-1,3 dextran

An understanding of Ab responses to polysaccharides associated with pathogenic microorganisms is of importance for improving vaccine design, especially in neonates that respond poorly to these types of Ags. In this study, we have investigated the role of the lymphoid-specific enzyme TdT in generating B cell clones responsive to alpha-1,3 dextran (DEX). TdT is a DNA polymerase that plays a major role in generating diversity of lymphocyte AgRs during V(D)J recombination. In this study, we show that the DEX-specific Ab response is lower, and the dominant DEX-specific J558 idiotype (Id) is not detected in TdT(-/-) mice when compared with wild-type (WT) BALB/c mice. Nucleotide sequencing of H chain CDR3s of DEX-specific plasmablasts, sorted postimmunization, showed that TdT(-/-) mice generate a lower frequency of the predominant adult molecularly determined clone J558. Complementation of TdT expression in TdT(-/-) mice by early forced expression of the short splice variant of TdT-restored WT proportions of J558 Id+ clones and also abrogated the development of the minor M104E Id+ clones. J558 Id V(D)J rearrangements are detected as early as 7 d after birth in IgM-negative B cell precursors in the liver and spleen of WT and TdT-transgenic mice but not in TdT(-/-) mice. These data show that TdT is essential for the generation of the predominant higher-affinity DEX-responsive J558 clone.

PI3 kinase signals BCR-dependent mature B cell survival

Previous work has shown that mature B cells depend upon survival signals delivered to the cells by their antigen receptor (BCR). To identify the molecular nature of this survival signal, we have developed a genetic approach in which ablation of the BCR is combined with the activation of specific, BCR dependent signaling cascades in mature B cells in vivo. Using this system, we provide evidence that the survival of BCR deficient mature B cells can be rescued by a single signaling pathway downstream of the BCR, namely PI3K signaling, with the FOXO1 transcription factor playing a central role.

Generation of B cell memory to the bacterial polysaccharide alpha-1,3 dextran

B1b B cells generate a novel form of memory and provide Ab mediated-protection to persisting bacterial pathogens. To understand how B1b B cells establish memory to polysaccharide Ags, we studied an oligoclonal B cell response to alpha-1,3 dextran (DEX) expressed on Enterobacter cloacae. B cells specific for DEX enrich in the marginal zone (MZ) and B1b B cell populations. After E. cloacae immunization, MZ B cells were responsible for the generation of initial peak DEX-specific Ab titers, whereas, DEX-specific B1b B cells expanded and played an important role in boosted production of DEX-specific Ab titers upon E. cloacae rechallenge. Cell transfer experiments demonstrate that B1b B cells possess the capacity for both robust proliferation and plasma cell differentiation, thus distinguishing themselves from MZ B cells, which uniformly commit to plasma cell differentiation. These results define B1b B cells as the principal reservoir for memory to bacterial-associated polysaccharide Ags.

Cathelicidin administration protects mice from Bacillus anthracis spore challenge

Cathelicidins are a family of cationic peptides expressed in mammals that possess numerous bactericidal and immunomodulatory properties. In vitro analyses showed that human, mouse, and pig cathelicidins inhibited Bacillus anthracis bacterial growth at micromolar concentrations in the presence or absence of capsule. Combined in vitro analyses of the effects of each peptide on spore germination and vegetative outgrowth by time lapse phase contrast microscopy, transmission electron microscopy, and flow cytometric analysis showed that only the pig cathelicidin was capable of directly arresting vegetative outgrowth and killing the developing bacilli within the confines of the exosporium. C57BL/6 mice were protected from spore-induced death by each cathelicidin in a time- and dose-dependent manner. Protection afforded by the porcine cathelicidin was due to its bactericidal effects, whereas the human and mouse cathelicidins appeared to mediate protection through increased recruitment of neutrophils to the site of infection. These findings suggest that cathelicidins might be utilized to augment the initial innate immune response to B. anthracis spore exposure and prevent the development of anthrax.

PIR-B-deficient mice are susceptible to Salmonella infection

Paired Ig-like receptors of activating (PIR-A) and inhibitory (PIR-B) isoforms are expressed by many hematopoietic cells, including B lymphocytes and myeloid cells. To determine the functional roles of PIR-A and PIR-B in primary bacterial infection, PIR-B-deficient (PIR-B(-/-)) and wild-type (WT) control mice were injected i.v. with an attenuated strain of Salmonella enterica Typhimurium (WB335). PIR-B(-/-) mice were found to be more susceptible to Salmonella infection than WT mice, as evidenced by high mortality rate, high bacterial loads in the liver and spleen, and a failure to clear bacteria from the circulation. Although blood levels of major cytokines and Salmonella-specific Abs were mostly comparable in the two groups of mice, distinct patterns of inflammatory lesions were found in their livers at 7-14 days postinfection: diffuse spreading along the sinusoids in PIR-B(-/-) mice vs nodular restricted localization in WT mice. PIR-B(-/-) mice have more inflammatory cells in the liver but fewer B cells and CD8(+) T cells in the spleen than WT mice at 14 days postinfection. PIR-B(-/-) bone marrow-derived macrophages (BMMphi) failed to control intracellular replication of Salmonella in vitro, in part due to inefficient phagosomal oxidant production, when compared with WT BMMphi. PIR-B(-/-) BMMphi also produced more nitrite and TNF-alpha upon exposure to Salmonella than WT BMMphi did. These findings suggest that the disruption of PIR-A and PIR-B balance affects their regulatory roles in host defense to bacterial infection.

Consequences of selection for improving production traits on the frequency of deleterious alleles for fitness

In this study the effect of artificial selection on BLUP EBV for production traits on the allele frequencies of a pleiotropic QTL affecting both production and disease susceptibility was investigated. Stochastic simulations were used to model artificial selection on a production trait that is controlled, in part, by a biallelic QTL that also controls susceptibility to disease. The QTL allele increasing production also increased susceptibility to disease. Different modes of action and proportions of variation accounted for by the QTL were assessed for the production trait. The main results indicated that alleles that confer susceptibility to the disease could be maintained in the population over a long period, depending on the mode of action of the QTL. In addition, the results of the study indicate that, under various conditions, it is possible to find pleiotropic QTL that control 2 traits despite these traits appearing to be uncorrelated. Therefore, in practice, an estimate of the genetic correlation between 2 traits may be misleading when the presence of such a QTL exists. The results of this study have implications for breeding programs. For example, if a pleiotropic QTL exists that favors heterozygotes for a production trait, it would be very difficult to remove disease susceptibility alleles via traditional selection methods.

Inbreeding effects on postweaning production traits, conformation, and calving performance in Irish beef cattle

The objective of this study was to quantify the effect of inbreeding on carcass quality, growth rate, live conformation measures, and calving performance in purebred populations of Charolais, Limousin, Simmental, Hereford, and Angus beef cattle using data from Irish commercial and pedigree herds. Variables analyzed are reflective of commercial farming practices. Inbreeding was included in a linear mixed model as either a class variable or a linear continuous variable. Nonlinear effects were nonsignificant across all traits. Inbred animals had decreased carcass weight and less carcass fat. The effects of inbreeding were more pronounced in the British beef breeds. Effects for carcass weight ranged from -0.87 kg (Charolais) to -1.90 kg (Hereford) per 1% increase in inbreeding. Inbred Charolais and Hereford animals were younger at slaughter by 3 and 5 d, respectively, per percentage of increase in inbreeding, whereas the effect of inbreeding on age at slaughter differed significantly with animal sex in the Limousin and Angus breeds. Inbred Limousin and Angus heifers were younger at slaughter by 5 and 7 d, respectively, per percentage of increase in inbreeding. Continental animals were more affected by inbreeding for live muscling and skeletal conformational measurements than the British breeds; inbred animals were smaller and narrower with poorer developed muscle. Calf inbreeding significantly affected perinatal mortality in Charolais, Simmental, and Hereford animals. The effects were dependent upon dam parity and calf sex; however, where significant, the association was always unfavorable. Dam inbreeding significantly affected perinatal mortality in Limousin and Hereford animals. Effects differed by parity in Limousins. Inbred first-parity Angus dams had a greater incidence of dystocia. Although the effects of inbreeding were some-times significant, they were small and are unlikely to make a large financial effect on commercial beef production in Ireland.

DNA microarray gene expression profile of marginal zone versus follicular B cells and idiotype positive marginal zone B cells before and after immunization with Streptococcus pneumoniae

Marginal zone (MZ) B cells play an important role in the clearance of blood-borne bacterial infections via rapid T-independent IgM responses. We have previously demonstrated that MZ B cells respond rapidly and robustly to bacterial particulates. To determine the MZ-specific genes that are expressed to allow for this response, MZ and follicular (FO) B cells were sort purified and analyzed via DNA microarray analysis. We identified 181 genes that were significantly different between the two B cell populations. Ninety-nine genes were more highly expressed in MZ B cells while 82 genes were more highly expressed in FO B cells. To further understand the molecular mechanisms by which MZ B cells respond so rapidly to bacterial challenge, Id-positive and -negative MZ B cells were sort purified before (0 h) or after (1 h) i.v. immunization with heat-killed Streptococcus pneumoniae, R36A, and analyzed via DNA microarray analysis. We identified genes specifically up-regulated or down-regulated at 1 h following immunization in the Id-positive MZ B cells. These results give insight into the gene expression pattern in resting MZ vs FO B cells and the specific regulation of gene expression in Ag-specific MZ B cells following interaction with Ag.