Ligation of surface Ig by gut-derived antigen positively selects chicken bursal and peripheral B cells.

In many mammals and birds, B cell lymphopoiesis takes place in GALT, such as the avian bursa of Fabricius. Although BCR expression is sufficient for bursal colonization, the role of BCR ligation in the later stages of bursal B cell lymphopoiesis remains elusive. To address this directly, we introduced a surface Ig-related construct with defined Ag specificity containing the Ag-binding portion of a lamprey variable lymphocyte receptor specific for PE fused to a truncated chicken μ-chain (VLR(PE)Tμ) into developing chick embryos.

Negative selection of self-reactive chicken B cells requires B cell receptor signaling and is independent of the bursal microenvironment.

Although the negative selection of self-reactive B cells in the bone marrow of mammals has been clearly demonstrated, it remains unclear in models of gut-associated B cell lymphopoiesis, such as that of the chicken (Gallus gallus). We have generated chicken surface IgM-related receptors in which the diversity region of the lamprey variable lymphocyte receptor (VLR) has been fused to the C region of chicken surface IgM (Tμ). Expression of a VLR:Tμ receptor with specificity for PE supported normal development of B cells, whereas a VLR:Tμ receptor specific to hen egg lysozyme (a self-antigen with respect to chicken B cells) induced, in vivo, complete deletion of VLR(HEL)Tμ-expressing B cells.

Prolonged effect of BAFF on chicken B cell development revealed by RCAS retroviral gene transfer in vivo.

Chickens provide an important model for developmental biology as well as phylogenetic studies of the immune system. In many species cytokines are important regulators of immune functions and recently we identified the chicken homologue of BAFF (B cell activating factor of the TNF family), shown to be an essential survival factor for B cells in mammals. Characterisation of BAFF function in the phylogenetically distant chicken requires in vivo studies, but despite considerable progress to date no efficient transgene or knockout technology for chickens is available.

Conservation of core gene expression in vertebrate tissues.

Background: Vertebrates share the same general body plan and organs, possess related sets of genes, and rely on similar physiological mechanisms, yet show great diversity in morphology, habitat and behavior. Alteration of gene regulation is thought to be a major mechanism in phenotypic variation and evolution, but relatively little is known about the broad patterns of conservation in gene expression in non-mammalian vertebrates.

Results: We measured expression of all known and predicted genes across twenty tissues in chicken, frog and pufferfish.

BLNK binds active H-Ras to promote B cell receptor-mediated capping and ERK activation.

Cross-linked B cell receptor (BCR) aggregates on the cell surface, then assembles into the "cap" where Ras is co-localized, and transduces various intracellular signals including Ras-ERK activation. BCR signals induce proliferation, differentiation, or apoptosis of B cells depending on their maturational stage. The adaptor protein BLNK binds various signaling proteins and Igalpha, a signaling subunit of the BCR complex, and plays an important role in the BCR signal transduction.

Ligand-independent signaling during early avian B cell development.

Surface immunoglobulin (sIg) expression has been conserved as a critical checkpoint in B lymphocyte development. In the chicken embryo, only sIg+ B cells are selectively expanded in the bursa of Fabricius, a primary lymphoid organ unique to the avian species. We have previously demonstrated that an interaction between the antigen- binding sites of sIg and a specific bursal ligand(s) is not required to regulate this developmental checkpoint.

Cell surface immunoglobulin regulated checkpoints in chicken B cell development.

The bursa of Fabricius is critical for the normal development of B lymphocytes in avian species. Productive colonization of bursal follicles by B cell precursors requires surface immunoglobulin expression. We have shown using retroviral gene transfer that expression of chimeric receptors containing the extracellular and transmembrane domains of murine CD8alpha and CD8beta fused to the cytoplasmic domains of chicken Igalpha and Igbeta can support productive bursal colonization in the chicken embryo in bursal cells lacking the expression of endogenous sIgM.

Antibodies, immunoglobulin genes and the bursa of Fabricius in chicken B cell development.

The bursa of Fabricius is critical for the normal development of B lymphocytes in birds. It is productively colonized during embryonic life by a limited number of B cell precursors that have undergone the immunoglobulin gene rearrangements required for expression of cell surface immunoglobulin. Immunoglobulin gene rearrangement occurs in the absence of terminal deoxynucleotidyl transferase and generates minimal antibody diversity.

Dual requirement for the Ig alpha immunoreceptor tyrosine-based activation motif (ITAM) and a conserved non-Ig alpha ITAM tyrosine in supporting Ig alpha beta-mediated B cell development.

Surface Ig (sIg) expression is a critical checkpoint during avian B cell development. Only cells that express sIg colonize bursal follicles, clonally expand, and undergo Ig diversification by gene conversion. Expression of a heterodimer, in which the extracellular and transmembrane domains of murine CD8alpha or CD8beta are fused to the cytoplasmic domains of chicken Igalpha (chIgalpha) or Igbeta, respectively (murine CD8alpha (mCD8alpha):chIgalpha + mCD8beta:chIgbeta), or an mCD8alpha:chIgalpha homodimer supported bursal B cell development as efficiently as endogenous sIg.

The avian B-cell receptor complex: distinct roles of Igalpha and Igbeta in B-cell development.

The bursa of Fabricius has evolved in birds as a gut-associated site of B-cell lymphopoiesis that is segregated from the development of other hematopoietic lineages. Despite differences in the developmental progression of chicken as compared to murine B-cell lymphopoiesis, cell-surface immunoglobulin (sIg) expression has been conserved in birds as an essential checkpoint in B-cell development. B-cell precursors that express an sIg complex that includes the evolutionarily conserved Igalpha/beta heterodimer colonize lymphoid follicles in the bursa, whereas B-cell precursors that fail to express sIg due to non-productive V(D)J recombination are eliminated.

The cytoplasmic domain of Ig alpha is necessary and sufficient to support efficient early B cell development.

The B cell receptor complex (BcR) is essential for normal B lymphocyte function, and surface BcR expression is a crucial checkpoint in B cell development. However, functional requirements for chains of the BcR during development remain controversial. We have used retroviral gene transfer to introduce components of the BcR into chicken B cell precursors during embryonic development.

Cell surface immunoglobulin receptors in B cell development.

Expression of surface immunoglobulin (sIg) related receptors has been conserved in phylogenetically distinct species as a critical checkpoint in B cell development. The sIg receptor comprises extracellular IgM heavy and light chains, with the potential for ligand binding, complexed to the Igalpha/Igbeta heterodimer that is responsible for signal transduction through sIg. Experimental systems, from both avian and murine models of B cell development, have been designed to identify the function of individual receptor components in B cell development.

Influence of antibody diversification on the mechanism of haplotype exclusion of immunoglobulin gene expression.

Allelic, or haplotype, exclusion of immunoglobulin gene expression ensures that the products of a single allele or light chain isotype are expressed on the B cell surface. Evidence has accumulated in rodent and primate models to indicate that the products of successful rearrangement regulate this process. In contrast, haplotype exclusion of chicken immunoglobulin gene expression is regulated at the level of variable region gene rearrangement.

B cell development in gut associated lymphoid tissues.

B lymphocyte development can occur in a variety of anatomical sites. While typically considered to be a process that occurs in the bone marrow throughout life, it is becoming clear that gut associates sites of B cell development are critically important in many species of veterinary importance. Among these sites, the bursa of Fabricius in chickens and the ileal Peyer's patches of sheep are among the best studied.