Chicken IgY binds its receptor at the CH3/CH4 interface similarly as the human IgA: Fc alpha RI interaction

Functional characterization of a plant-produced infectious bursal disease virus antigen fused to the constant region of avian IgY immunoglobulins

Infectious bursal disease virus (IBDV) is the cause of an economically important highly contagious disease of poultry, and vaccines are regarded as the most beneficial interventions for its prevention. In this study, plants were used to produce a recombinant chimeric IBDV antigen for the formulation of an innovative subunit vaccine. The fusion protein (PD-FcY) was designed to combine the immunodominant projection domain (PD) of the viral structural protein VP2 with the constant region of avian IgY (FcY), which was selected to enhance antigen uptake by avian immune cells. The gene construct encoding the fusion protein was transiently expressed in Nicotiana benthamiana plants and an extraction/purification protocol was set up, allowing to reduce the contamination by undesired plant compounds/proteins. Mass spectrometry analysis of the purified protein revealed that the glycosylation pattern of the FcY portion was similar to that observed in native IgY, while in vitro assays demonstrated the ability of PD-FcY to bind to the avian immunoglobulin receptor CHIR-AB1. Preliminary immunization studies proved that PD-FcY was able to induce the production of protective anti-IBDV-VP2 antibodies in chickens. In conclusion, the proposed fusion strategy holds promises for the development of innovative low-cost subunit vaccines for the prevention of avian viral diseases.

FcαRI binding at the IgA1 CH2-CH3 interface induces long-range conformational changes that are transmitted to the hinge region

IgA effector functions include proinflammatory immune responses triggered upon clustering of the IgA-specific receptor, FcαRI, by IgA immune complexes. FcαRI binds to the IgA1-Fc domain (Fcα) at the C_H2-C_H3 junction and, except for C_H2 L257 and L258, all side-chain contacts are contributed by the C_H3 domain. In this study, we used experimental and computational approaches to elucidate energetic and conformational aspects of FcαRI binding to IgA. The energetic contribution of each IgA residue in the binding interface was assessed by alanine-scanning mutagenesis and equilibrium surface plasmon resonance (SPR). As expected, hydrophobic residues central to the binding site have strong energetic contributions to the FcαRI:Fcα interaction. Surprisingly, individual mutation of C_H2 residues L257 and L258, found at the periphery of the FcαRI binding site, dramatically reduced binding affinity. Comparison of antibody:receptor complexes involving IgA or its precursor IgY revealed a conserved receptor binding site at the C_H2-C_H3 junction (or its equivalent). Given the importance of residues near the C_H2-C_H3 junction, we used coarse-grained Langevin dynamics simulations to understand the functional dynamics in Fcα. Our simulations indicate that FcαRI binding, either in an asymmetric (1:1) or symmetric (2:1) complex with Fcα, propagated long-range conformational changes across the Fc domains, potentially impacting the hinge and Fab regions. Subsequent SPR experiments confirmed that FcαRI binding to the Fcα C_H2-C_H3 junction altered the kinetics of HAA lectin binding at the IgA1 hinge. Receptor-induced long-distance conformational transitions have important implications for the interaction of aberrantly glycosylated IgA1 with anti-glycan autoantibodies in IgA nephropathy.

Insights into the chicken IgY with emphasis on the generation and applications of chicken recombinant monoclonal antibodies

The advantages of chicken (Gallus gallus domesticus) antibodies as immunodiagnostic and immunotherapeutic biomolecules has only been recently recognized. Even so, chicken antibodies remain less-well characterized than their mammalian counterparts. This review aims at providing a current overview of the structure, function, development and generation of chicken antibodies. Additionally, brief but comprehensive insights into current knowledge pertaining to the immunogenetic framework and diversity-generation of the chicken immunoglobulin repertoire which have contributed to the establishment of recombinant chicken mAb-generating methods are discussed. Focus is provided on the current methods used to generate antibodies from chickens with added emphasis on the generation of recombinant chicken mAbs and its derivative formats. The advantages and limitations of established protocols for the generation of chicken mAbs are highlighted. The various applications of recombinant chicken mAbs and its derivative formats in immunodiagnostics and immunotherapy are further detailed.

Identification of an Activating Chicken Ig-like Receptor Recognizing Avian Influenza Viruses

Chicken Ig-like receptors (CHIRs) represent a multigene family encoded by the leukocyte receptor complex that encodes a variety of receptors that are subdivided into activating CHIR-A, inhibitory CHIR-B, and bifunctional CHIR-AB. Apart from CHIR-AB, which functions as an Fc receptor, CHIR ligands are unknown. In the current study, we used a panel of different BWZ.36 CHIR reporter cells to identify an interaction between specific CHIRs and avian influenza virus (AIV). The specificity of the CHIR-AIV interaction was further demonstrated using CHIR fusion proteins that bound to AIV-coated plates and were able to reduce the interaction of reporter cells with AIV. There was no difference in binding of CHIR to different AIV strains. Furthermore, CHIR fusion proteins reduced AIV-induced in vitro activation of NK cells obtained from lungs of AIV-infected animals, as judged by the lower frequency of CD107⁺ cells. Because the original CHIR reporter lines were generated based on sequence information about extracellular CHIR domains, we next identified a full-length CHIR that displayed similar binding to AIV. The sequence analysis identified this CHIR as a CHIR-A. Neuraminidase treatment of coated CHIR-human Ig proteins reduced binding of trimeric H5 proteins to CHIR. This suggests that the interaction is dependent on sialic acid moieties on the receptor. In conclusion, this article identifies AIV as a ligand of CHIR-A and describes the functional consequences of this interaction.

Human IgG4: a structural perspective

IgG4, the least represented human IgG subclass in serum, is an intriguing antibody with unique biological properties, such as the ability to undergo Fab-arm exchange and limit immune complex formation. The lack of effector functions, such as antibody-dependent cell-mediated cytotoxicity and complement-dependent cytotoxicity, is desirable for therapeutic purposes. IgG4 plays a protective role in allergy by acting as a blocking antibody, and inhibiting mast cell degranulation, but a deleterious role in malignant melanoma, by impeding IgG1-mediated anti-tumor immunity. These findings highlight the importance of understanding the interaction between IgG4 and Fcγ receptors. Despite a wealth of structural information for the IgG1 subclass, including complexes with Fcγ receptors, and structures for intact antibodies, high-resolution crystal structures were not reported for IgG4-Fc until recently. Here, we highlight some of the biological properties of human IgG4, and review the recent crystal structures of IgG4-Fc. We discuss the unexpected conformations adopted by functionally important Cγ2 domain loops, and speculate about potential implications for the interaction between IgG4 and FcγRs.

An ELISA for quantifying quail IgY and characterizing maternal IgY transfer to egg yolk in several quail strains

In avian species, maternal blood immunoglobulin Y (IgY) is transferred to the egg yolks of maturing oocytes, but the mechanism underlying this transfer is unknown. To gain insight into the mechanism of maternal IgY transfer in quail, we established an enzyme-linked immunosorbent assay (ELISA) for the quantitation of quail IgY. We characterized strain differences in blood and egg yolk IgY concentrations and exogenously injected IgY-Fc uptakes into egg yolks. A specific rabbit polyclonal antibody to quail IgY was raised for the ELISA. Blood and egg yolk IgY concentrations were determined in six quail strains (one inbred strain, L; four closed population strains, AWE, DB, PS, WE; one commercial strain, Commercial). The birds were also injected with digoxigenin-labeled quail IgY-Fc, and its uptakes into laid eggs were compared. The strain difference in blood and egg yolk IgY concentrations was at most 2.5-fold, between PS and AWE. The rank order of IgY concentrations was AWE, Commercial, DB, L≥WE≥PS. A significant positive correlation (|R|=0.786) between individual blood IgY and egg yolk IgY and the concentrated egg yolk IgY (1.5-2-fold) against blood IgY was observed. Interestingly, there was a significant inverse correlation (|R|=0.452) between injected IgY-Fc uptakes and the blood IgY concentration, implying competition of the injected IgY-Fc and blood IgY in the process of IgY uptake into egg yolks. In conclusion, we successfully determined blood and egg yolk IgY concentrations in various quail strains by a quail IgY-specific ELISA. The concentrated egg yolk IgY against the blood IgY and the inverse relationship of exogenous IgY-Fc uptake against the blood IgY supports the existence of a selective IgY transport mechanism in avian maturing oocytes.

A bioinformatic approach to check the spatial epitope structure of an immunogenic protein coded by DNA vaccine plasmids

In this study, we used an approach to check the Hemagglutinin antigen-antibodies interactions after fusion of one or two gene segments to Hemagglutinin gene in some influenza DNA vaccines. We designed different DNA vaccine constructs containing Hemagglutinin 9 (H9) gene fused to four or eight 29 amino acids of C3d (4/8P29C3d) and/or 3, 4 domains of the Fc part of IgY (FcIgY) coding sequences. As there are receptors for P29C3d and FcIgY on the immune cells, fused H9 are targeted to these cells. Three dimensional (3D) structures of the DNA vaccine coded proteins were modeled and docked with two antibodies (1KEN, 1QFU) to evaluate the effect of the H9 gene fusion to the other gene segments (4, 8 P29C3d and FcIgY) on the interaction of two H9 spatial epitopes. Also, we docked DNA vaccine proteins containing Fc IgY to its receptor (CHIR AB1) and compare interaction affinity of Fc IgY alone with affinity of DNA vaccines containing Fc IgY. The average of 1KEN and 1QFU interface scores were 94.89 and 93.09% of H9 DNA vaccine-antibodies interface scores, respectively. These percentages showed a little change in the H9 immunogenic parts. Also, because of spatial freedom of H9 part in all DNA vaccine proteins, added parts may not interfere with antibody-antigen interactions. Once, H9+FcIgY and CHIR AB1 affinity decreased in comparison with affinity of Fc IgY alone and CHIR AB1, affinity of H9+8P29C3d+FcIgY and CHIR AB1 increased to 132%. So, this would be expectable that despite of loss of affinity in H9 and its antibodies in the H9+8P29C3d+FcIgY, dramatic increase of Fc IgY and CHIR AB1 affinity in this group, could repair the loss of H9 affinity and may lead to a better immunogenicity.

M2e-Based Universal Influenza A Vaccines

The successful isolation of a human influenza virus in 1933 was soon followed by the first attempts to develop an influenza vaccine. Nowadays, vaccination is still the most effective method to prevent human influenza disease. However, licensed influenza vaccines offer protection against antigenically matching viruses, and the composition of these vaccines needs to be updated nearly every year. Vaccines that target conserved epitopes of influenza viruses would in principle not require such updating and would probably have a considerable positive impact on global human health in case of a pandemic outbreak. The extracellular domain of Matrix 2 (M2e) protein is an evolutionarily conserved region in influenza A viruses and a promising epitope for designing a universal influenza vaccine. Here we review the seminal and recent studies that focused on M2e as a vaccine antigen. We address the mechanism of action and the clinical development of M2e-vaccines. Finally, we try to foresee how M2e-based vaccines could be implemented clinically in the future.

Fc receptors for immunoglobulins and their appearance during vertebrate evolution

Receptors interacting with the constant domain of immunoglobulins (Igs) have a number of important functions in vertebrates. They facilitate phagocytosis by opsonization, are key components in antibody-dependent cellular cytotoxicity as well as activating cells to release granules. In mammals, four major types of classical Fc receptors (FcRs) for IgG have been identified, one high-affinity receptor for IgE, one for both IgM and IgA, one for IgM and one for IgA. All of these receptors are related in structure and all of them, except the IgA receptor, are found in primates on chromosome 1, indicating that they originate from a common ancestor by successive gene duplications. The number of Ig isotypes has increased gradually during vertebrate evolution and this increase has likely been accompanied by a similar increase in isotype-specific receptors. To test this hypothesis we have performed a detailed bioinformatics analysis of a panel of vertebrate genomes. The first components to appear are the poly-Ig receptors (PIGRs), receptors similar to the classic FcRs in mammals, so called FcRL receptors, and the FcR γ chain. These molecules are not found in cartilagous fish and may first appear within bony fishes, indicating a major step in Fc receptor evolution at the appearance of bony fish. In contrast, the receptor for IgA is only found in placental mammals, indicating a relatively late appearance. The IgM and IgA/M receptors are first observed in the monotremes, exemplified by the platypus, indicating an appearance during early mammalian evolution. Clearly identifiable classical receptors for IgG and IgE are found only in marsupials and placental mammals, but closely related receptors are found in the platypus, indicating a second major step in Fc receptor evolution during early mammalian evolution, involving the appearance of classical IgG and IgE receptors from FcRL molecules and IgM and IgA/M receptors from PIGR.

Chicken CRTAM binds nectin-like 2 ligand and is upregulated on CD8+ αβ and γδ T lymphocytes with different kinetics

During a search for immunomodulatory receptors in the chicken genome, we identified a previously cloned chicken sequence as CRTAM homologue by its overall identity and several conserved sequence features. For further characterization, we generated a CRTAM specific mab. No staining was detectable in freshly isolated cell preparations from thymus, bursa, caecal tonsils, spleen, blood and intestine. Activation of splenocytes with recombinant IL-2 increased rapid CRTAM expression within a 2 h period on about 30% of the cells. These CRTAM⁺ cells were identified as CD8⁺ γδ T lymphocytes. In contrast, CRTAM expression could not be stimulated on PBL with IL-2, even within a 48 h stimulation period. As a second means of activation, T cell receptor (TCR) crosslinking using an anti-αβ-TCR induced CRTAM on both PBL and splenocytes. While CRTAM expression was again rapidly upregulated on splenocytes within 2 h, it took 48 h to reach maximum levels of CRTAM expression in PBL. Strikingly, albeit the stimulation of splenocytes was performed with anti-αβ-TCR, CRTAM expression after 2 h was mainly restricted to CD8⁺ γδ T lymphocytes, however, the longer anti-TCR stimulation of peripheral blood lymphocytes (PBL) resulted in CRTAM expression on αβ T lymphocytes. In order to characterize the potential ligand we cloned and expressed chicken Necl-2, a member of the nectin and nectin-like family which is highly homologous to its mammalian counterpart. Three independent assays including a reporter assay, staining with a CRTAM-Ig fusion protein and a cell conjugate assay confirmed the interaction of CRTAM with Necl-2 which could also be blocked by a soluble CRTAM-Ig fusion protein or a CRTAM specific mab. These results suggest that chicken CRTAM represents an early activation antigen on CD8⁺ T cells which binds to Necl-2 and is upregulated with distinct kinetics on αβ versus γδ T lymphocytes.

Structural determinants of unique properties of human IgG4-Fc

Human IgG4, normally the least abundant of the four subclasses of IgG in serum, displays a number of unique biological properties. It can undergo heavy-chain exchange, also known as Fab-arm exchange, leading to the formation of monovalent but bispecific antibodies, and it interacts poorly with FcγRII and FcγRIII, and complement. These properties render IgG4 relatively “non-inflammatory” and have made it a suitable format for therapeutic monoclonal antibody production. However, IgG4 is also known to undergo Fc-mediated aggregation and has been implicated in auto-immune disease pathology. We report here the high-resolution crystal structures, at 1.9 and 2.35 Å, respectively, of human recombinant and serum-derived IgG4-Fc. These structures reveal conformational variability at the C_H3–C_H3 interface that may promote Fab-arm exchange, and a unique conformation for the FG loop in the C_H2 domain that would explain the poor FcγRII, FcγRIII and C1q binding properties of IgG4 compared with IgG1 and -3. In contrast to other IgG subclasses, this unique conformation folds the FG loop away from the C_H2 domain, precluding any interaction with the lower hinge region, which may further facilitate Fab-arm exchange by destabilisation of the hinge. The crystals of IgG4-Fc also display Fc–Fc packing contacts with very extensive interaction surfaces, involving both a consensus binding site in IgG-Fc at the C_H2–C_H3 interface and known hydrophobic aggregation motifs. These Fc–Fc interactions are compatible with intact IgG4 molecules and may provide a model for the formation of aggregates of IgG4 that can cause disease pathology in the absence of antigen.

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The first high-resolution crystal structures of IgG4-Fc have been solved.

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Arg409 adopts two conformations, each with a different effect on the C_H3–C_H3 interface.

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Crystal packing analysis reveals a novel Fc–Fc interface.

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The C_H2 domain FG loop adopts a unique conformation, affecting FcγR and C1q binding.

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The IgG4-Fc crystal structures explain unique biological properties of IgG4.

Chicken immunoregulatory Ig-like receptor families: an overview and expression details on ggTREM-A1

Paired immunoregulatory receptors facilitate the coordination of the immune response at the cellular level. In recent years, our group characterized chicken homologues to mammalian immunoregulatory Ig-like receptor families. The first part of this review focuses on the current progress on chicken immunoregulatory Ig-like receptor families. One of these receptors is gallus gallus TREM-A1, which was described as the only member of the chicken TREM family with activating potential. The second part of this review presents a study initiated to further characterize ggTREM-A1 expression. For this purpose we established real-time RT-PCR and generated a specific mab to analyze the expression profile of ggTREM-A1 on mRNA and protein level, respectively. GgTREM-A1 mRNA was predominantly expressed in macrophages, but was also detected in brain, bone marrow, bursa, thymus, spleen and PBMC. Analyzing ggTREM-A1 surface expression by mab staining validated the expression on macrophages. Additionally, we showed high expression on blood monocytes, heterophils and NK cells and on monocytes isolated from bone marrow. Moreover, we detected ggTREM-A1 protein also on thrombocytes, B and T cell subsets, but antigen expression seemed to be lower and more variable in these cells. Immunohistochemistry of chicken brain tissue, combining ggTREM-A1 mab and various markers specific for various brain cell subsets showed expression of ggTREM-A1 on microglial cells, but also on neurons, astrocytes and oligodendrocytes. In conclusion, ggTREM-A1 is expressed on a variety of cells, relevant for the immune system, possibly combining physiological function of different mammalian TREM.

Chicken NK cell receptors

Natural killer cells are innate immune cells that destroy virally infected or transformed cells. They recognize these altered cells by a plethora of diverse receptors and thereby differ from other lymphocytes that use clonally distributed antigen receptors. To date, several receptor families that play a role in either activating or inhibiting NK cells have been identified in mammals. In the chicken, NK cells have been functionally and morphologically defined, however, a conclusive analysis of receptors involved in NK cell mediated functions has not been available. This is partly due to the low frequencies of NK cells in blood or spleen that has hampered their intensive characterization. Here we will review recent progress regarding the diverse NK cell receptor families, with special emphasis on novel families identified in the chicken genome with potential as chicken NK cell receptors.

Defense genes missing from the flight division

Birds have a smaller repertoire of immune genes than mammals. In our efforts to study antiviral responses to influenza in avian hosts, we have noted key genes that appear to be missing. As a result, we speculate that birds have impaired detection of viruses and intracellular pathogens. Birds are missing TLR8, a detector for single-stranded RNA. Chickens also lack RIG-I, the intracellular detector for single-stranded viral RNA. Riplet, an activator for RIG-I, is also missing in chickens. IRF3, the nuclear activator of interferon-beta in the RIG-I pathway is missing in birds. Downstream of interferon (IFN) signaling, some of the antiviral effectors are missing, including ISG15, and ISG54 and ISG56 (IFITs). Birds have only three antibody isotypes and IgD is missing. Ducks, but not chickens, make an unusual truncated IgY antibody that is missing the Fc fragment. Chickens have an expanded family of LILR leukocyte receptor genes, called CHIR genes, with hundreds of members, including several that encode IgY Fc receptors. Intriguingly, LILR homologues appear to be missing in ducks, including these IgY Fc receptors. The truncated IgY in ducks, and the duplicated IgY receptor genes in chickens may both have resulted from selective pressure by a pathogen on IgY FcR interactions. Birds have a minimal MHC, and the TAP transport and presentation of peptides on MHC class I is constrained, limiting function. Perhaps removing some constraint, ducks appear to lack tapasin, a chaperone involved in loading peptides on MHC class I. Finally, the absence of lymphotoxin-alpha and beta may account for the observed lack of lymph nodes in birds. As illustrated by these examples, the picture that emerges is some impairment of immune response to viruses in birds, either a cause or consequence of the host-pathogen arms race and long evolutionary relationship of birds and RNA viruses.

Avian IgY is selectively incorporated into the egg yolks of oocytes by discriminating Fc amino acid residues located on the Cυ3/Cυ4 interface

In avian species, maternal IgY is selectively incorporated into the egg yolks of maturing oocytes, but the relevance of receptor-mediated uptake is unclear. Here we investigated the critical amino acid residues of IgY required for egg yolk transport by conducting mutational analyses of selected residues located along the Cυ3 and Cυ4 domains of chicken IgY. Recombinant wild-type IgY-Fc (WT) and its mutants were synthesized, and their uptakes into the egg yolks of quail were determined. Among the 17 amino acid residues located on the Cυ3/Cυ4 interface, the substitution of Y363 at the Cυ3 domain to alanine abolished the IgY-Fc uptake into egg yolks. The comprehensive substitution of Y363 with other amino acids revealed that the residue at 363 needs to be allocated with aromatic amino acids to maintain the high transport ability. The deglycosylation of the N-linked carbohydrate chain by substituting N407 at the Cυ3 domain with alanine also caused a marked reduction of IgY-Fc uptake. The microscopic detection of the injected WT and Y363A mutant in ovarian follicles showed that the WT was concentrically accumulated in yolk granules, whereas the Y363A mutant was hardly accumulated in yolk granules, but it had infiltrated into the granulosa cell layer, suggesting that a major hurdle disturbing the infiltration of the Y363A mutant lies on the inside of the granulosa cell layer. The identification of important amino acid residues required for efficient IgY transport enhances our understanding of the molecular mechanisms underlying IgY transport through a specific IgY receptor in ovarian follicles.

The Turkey Ig-like receptor family: identification, expression and function

The chicken leukocyte receptor complex located on microchromosome 31 encodes the chicken Ig-like receptors (CHIR), a vastly expanded gene family which can be further divided into three subgroups: activating CHIR-A, bifunctional CHIR-AB and inhibitory CHIR-B. Here, we investigated the presence of CHIR homologues in other bird species. The available genome databases of turkey, duck and zebra finch were screened with different strategies including BLAST searches employing various CHIR sequences, and keyword searches. We could not identify CHIR homologues in the distantly related zebra finch and duck, however, several partial and complete sequences of CHIR homologues were identified on chromosome 3 of the turkey genome. They were designated as turkey Ig-like receptors (TILR). Using cDNA derived from turkey blood and spleen RNA, six full length TILR could be amplified and further divided according to the typical sequence features into one activating TILR-A, one inhibitory TILR-B and four bifunctional TILR-AB. Since the TILR-AB sequences all displayed the critical residues shown to be involved in binding to IgY, we next confirmed the IgY binding using a soluble TILR-AB1-huIg fusion protein. This fusion protein reacted with IgY derived from various gallinaceous birds, but not with IgY from other bird species. Finally, we tested various mab directed against CHIR for their crossreactivity with either turkey or duck leukocytes. Whereas no staining was detectable with duck cells, the CHIR-AB1 specific mab 8D12 and the CHIR-A2 specific mab 13E2 both reacted with a leukocyte subpopulation that was further identified as thrombocytes by double immunofluorescence employing B-cell, T-cell and thrombocyte specific reagents. In summary, although the turkey harbors similar LRC genes as the chicken, their distribution seems to be distinct with predominance on thrombocytes rather than lymphocytes.

Avian IgY antibodies and their recombinant equivalents in research, diagnostics and therapy

The generation and use of avian antibodies is of increasing interest in a wide variety of applications within the life sciences. Due to their phylogenetic distance, mechanisms of immune diversification and the way in which they deposit IgY immunoglobulin in the egg yolk, chickens provide a number of advantages compared to mammals as hosts for immunization. These advantages include: the one-step purification of antibodies from egg yolk in large amounts facilitates having a virtually continuous supply; the epitope spectrum of avian antibodies potentially grants access to novel specificities; the broad absence of cross-reactivity with mammalian epitopes avoids assay interference and improves the performance of immunological techniques. The polyclonal nature of IgY antibodies has limited their use since avian hybridoma techniques are not well established. Recombinant IgY, however, can be generated from mammalian monoclonal antibodies which makes it possible to further exploit the advantageous properties of the IgY scaffold. Moreover, cloning and selecting the immune repertoire from avian organisms is highly efficient, yielding antigen-specific antibody fragments. The recombinant approach is well suited to circumvent any limitations of polyclonal antibodies. This review presents comprehensive information on the generation, purification, modification and applications of polyclonal and monoclonal IgY antibodies.

A striking example of convergent evolution observed for the ggFcR:IgY interaction closely resembling that of mammalian FcR:IgG

We have recently identified a novel IgY specific chicken FcR (ggFcR) on chromosome 20, a region where no FcR gene is present in mammals. Serially deleted IgY fusion proteins were tested in a reporter assay to identify C(H) domains involved in ggFcR binding. Single C(H) domains did not bind to ggFcR, whereas Fcυ2 to Fcυ4 induced good and the Fcυ3 to Fcυ4 domains moderate activity. When IgY from diverse birds were assayed, only IgY from gallinaceous birds showed binding, which enabled us to pinpoint several potential contact sites by a sequence comparison and molecular modelling. Point mutations of critical residues at these sites revealed the Fcυ2 and Fcυ3 domains as major ggFcR:IgY binding sites similar to mammalian IgG. These results demonstrate that ggFcR has a contact site to IgY which closely resembles that of human IgG bound to FcR.

Immunoglobulin genetics and antibody responses to influenza in ducks

The role of the duck as the natural host and reservoir of influenza and efforts to vaccinate ducks during recent outbreaks of avian influenza has renewed interest in the duck antibody response. Ducks have unique antibody structures and expression, with consequences for their function. Aspects of immunoglobulin genetics, gene expression, and antibody function will be reviewed in the context of the duck immune response to influenza. Ducks have three immunoglobulin isotypes, IgM, IgA and IgY in translocon arrangement. The order of heavy chain genes in the locus is unusual, IGHM, IGHA and IGHY, with IGHA in inverse transcriptional orientation. IgH and IgL gene rearrangement in ducks involves limited V, (D) and J element recombination and diversity is generated by gene conversion from pseudogenes. IgY, the functional equivalent of IgG, is produced in two secreted forms, a full-length form and one lacking the third and fourth C region domains, which predominates later in the immune response and lacks the biological effector functions of IgG. The unusual features of duck antibodies may contribute to weak antibody responses and the perpetuation of the virus in this animal reservoir.

The chicken leukocyte receptor cluster

Receptors of the immunoglobulin-like superfamily are critically involved in virtually every aspect of immune responses. One large chromosomal area encoding such immunoregulatory receptors is the leukocyte receptor cluster. Here we review various aspects of the chicken Ig-like receptor (CHIR) family, located on microchromosome 31, an orthologous position to the mammalian leukocyte receptor cluster. The CHIR family has been massively expanded with over hundred CHIR genes that are further distinguished into activating, inhibitory and bifunctional receptors. Comparisons of various features such as amino acid motifs, genomic structure, expression and associated adaptor molecules reveal the homology of CHIR to both the killer Ig-like and the leukocyte Ig-like receptor families, with most pronounced correlation of certain CHIR to the NK cell receptor KIR2DL4. To date the CHIR ligands remain largely obscure with the exception of CHIR-AB1 that binds to chicken IgY. Detailed analyses of CHIR-AB1, its crystal structure, the interaction to IgY and functional capabilities allow us to draw conclusions regarding Fc receptor phylogeny and function.

Passive immune-protection of small abalone against Vibrio alginolyticus infection by anti-Vibrio IgY-encapsulated feed

Small abalone (Haliotis diversicolor supertexta) is a high value-added shellfish. It however has been suffering Vibrio alginolyticus infections, which cause mass death of small abalone and thus great economic losses, particularly in artificial aquaculture. In this study, we attempted to treat small abalone with anti-Vibrio IgY to elicit a passive immunity directly against V. alginolyticus infections. Anti-Vibrio IgY was alginate encapsulated in egg powders as feed, which may avoid antibody inactivation in the gastrointestinal tract of small abalone. The feed was tested for the stability of anti-Vibrio IgY in a gastrointestinal mimic environment. The result showed anti-Vibrio IgY retained activity as high as 90% after 4 h exposure to pancreatic enzymes. Addition of 0, 5 or 10% anti-Vibrio IgY-encapsulated egg powders into a basal diet to form abalone diet formulae. Small abalones fed with the anti-Vibrio IgY formulae showed a relatively high respiratory burst activity than those without anti-Vibrio IgY treatments. The survival rates of small abalones fed with 5 or 10% anti-Vibrio IgY egg powders were in the range of 65-70% 14 days post-V. alginolyticus challenge (1 x 10⁶ c.f.u.), which was significantly higher than 0% of those fed without anti-Vibrio IgY. The anti-Vibrio IgY-encapsulated formulae were thus concluded to be an effective means to prevent small abalone from V. alginolyticus infection, and may be practical in use in abalone aquaculture.

The red jungle fowl leukocyte receptor complex contains a large, highly diverse number of chicken immunoglobulin-like receptor (CHIR) genes

The chicken Ig-like receptor (CHIR) gene family is located on microchromosome 31, the orthologous region to the mammalian leukocyte receptor complex. CHIR are equally related to the mammalian killer Ig-like receptors and leukocyte Ig-like transcripts, but they occur in a much higher number and diversity. The chicken microchromosome 31 has been neglected in the genome sequence analysis. Here, we provide a first analysis of this region. For this purpose bacterial artificial chromosome (BAC) sequences originating from a single inbred red jungle fowl that served as basis for the chicken genome project were screened for the presence of CHIR sequences and eight BACs were identified as major CHIR containing regions. Since the sequences of these BACs that were available in the database were not complete, sequence gaps were further closed by novel data from the chicken genome project. The entire sequence was aligned into 26 contigs covering 875kbp that contained 84 functional CHIR and 46 CHIR pseudogenes that were hampered by different reasons such as premature stop codons. The 84 functional CHIR were further categorized into 35 activating (CHIRA), 26 inhibitory (CHIRB) and 23 bifunctional (CHIRAB) genes. A detailed comparison of the annotated sequence taking also into account the previously published CHIR BAC sequence originating from an Lohman selected leghorn chicken revealed that the CHIR locus seems to be a very active region with a high degree of gene reorganization that resembles a constant birth and death evolution. The present report provides a framework for the future completion of the CHIR locus. It further suggests that the entire microchromosome 31 may resemble a locus of extraordinary genomic diversity that is beneficial for the development of a large CHIR repertoire, but that has therefore lost all other genes, where such a diversification would be fatal.

Channel catfish soluble FcmuR binds conserved linear epitopes present on Cmu3 and Cmu4

A linear epitope on catfish IgM has been identified as the docking site for the catfish soluble FcmuR (IpFcRI). Western blot analyses and latex bead binding assays identified the consensus octapeptide motif FxCxVxHE located at the second cysteine that forms the intrachain disulfide bond of the catfish Cmu3 and Cmu4 immunolglobulin (Ig) domains as the IpFcRI binding sites. Furthermore, molecular modeling of catfish Cmu3 and Cmu4 confirmed that the octapeptide in both of these domains is accessible for IpFcRI interactions. In addition, since this octapeptide motif is also found in other vertebrate Ig domains, IpFcRI binding to Ig heavy (H) and light (L) chains from rainbow trout, chicken, mouse, rabbit, and goat were examined by Western blot analyses and latex bead binding assays. IpFcRI readily bound reduced rainbow trout (Igmu), chicken (Ignu), mouse (Igmu, Iggamma1, Iggamma2a, Iggamma2b, and Igalpha), rabbit (Igmu and Iggamma) and goat (Iggamma) IgH chains, and mouse Igkappa and Iglambda, and chicken Iglambda IgL chains. IpFcRI also bound mouse IgM, IgA and IgG subclasses when examined under native conditions.