Brief review of the chicken Major Histocompatibility Complex: the genes, their distribution on chromosome 16, and their contributions to disease resistance

The chicken major histocompatibility complex (MHC-B) and alloantigen systems A, D, E, and I impact resistance to coccidiosis

Coccidiosis, a major poultry protozoal disease caused by several Eimeria species, compromises gut health causing significant losses. This study assessed the association of haplotypes of the major histocompatibility complex (MHC) and other blood alloantigens found in commercial egg production chickens with resistance to coccidiosis. Pedigreed White Leghorn offspring segregating for the MHC-B region, plus four additional alloantigen systems A (C4BPM), D (CD99), E (FCAMR), and I (RHCE) were tested for differential resistance to coccidiosis in five 26-day (d) trials (n= 235 birds in total). On d 19, all birds were inoculated with a cocktail of E. acervulina, E. maxima, and E. tenella oocysts and allocated to individual cages. Phenotypes evaluated included body weight gain (BWG), feed intake (FI), feed conversion ratio (FCR), gross and microscopic lesion scores (GLS and MLS), and oocyst shedding (oocysts per gram, OPG). Haplotypes of the five blood systems were determined by SNP genotyping. A positive and negative association means an increase and decrease in a phenotypic trait, respectively, with each additional copy (0, 1 or 2) of a given haplotype. Results were considered statistically significant at P ≤ 0.05. The CD99-H01 haplotype association was positive with BWG but negative with FCR. Genotype B21B21 had the highest GLS in the jejunum establishing a positive association between MHC B21 and jejunal GLS. Further, the B12B15 genotype had a lower E. maxima OPG compared with the B12B21 genotype. The I system I-H01 haplotype had a negative association with jejunal and cecal GLS. Duodenal GLS was lower in E-H02/H02 compared to the E-H07/H07 genotype of the E system. Haplotypes B21, blood systems D-H01, E-H02, and I-H01 were associated with improved resistance to coccidiosis. The association of specific haplotypes of the MHC-B and other alloantigen systems D, E, and I with resistance and susceptibility traits during mixed Eimeria infection underscores the need for further investigations of these haplotypes' effects on coccidiosis resistance in commercial lines, validating the inclusion of different blood systems in selection programs.

The MHC (Major Histocmpatibility Complex) Exceptional Molecules of Birds and Their Relationship to Diseases

There are about 5000 species of Passeriformes birds, which are half of the extant ones. Their class I MHC molecules are found to be different from all other studied vertebrates, including other bird species; i.e., amino acid residues 10 and 96 are not the seven canonic residues extant in all other vertebrate molecules. Thus, the canonic residues in MHC class I vertebrate molecules are reduced to five. These differences have physical effects in MHC (Major Histocompatibility Complex) class I alpha chain interaction with beta-2-microglobulin but have yet unknown functional effects. Also, introns show specific Passeriformes distinction both in size and invariance. The studies reviewed in this paper on MHC structure have been done in wild birds that cover most of the world's passerine habitats. In this context, we are going to expose the most commonly occurring bird diseases with the caveat that MHC and disease linkage pathogenesis is not resolved. In addition, this field is poorly studied in birds; however, common bird diseases like malaria and Marek's disease are linked to MHC. On the other hand, the main established function of MHC molecules is presenting microbial and other antigens to T cells in order to start immune responses, and they also may modulate the immune system through NK receptors and other receptors (non-classical class I MHC molecules). Also, structural and polymorphic differences between classical class I molecules and non-classical class I molecules are at present not clear, and their definition is blurred. These passerine exceptional MHC class I molecules may influence linkage to diseases, transplantation, and other MHC presentation and self-protection functions. Further studies in more Passeriformes species are ongoing and needed.

The search to understand the development of the chicken immune system: Differences in expression of MHC class I loci and waves of thymocytes as evolutionary relics?

Chickens are renowned as a model for embryogenesis but have also been responsible for crucial advances in virology, cancer research and immunology. However, chickens are best known as a major source of animal protein for human nutrition, with roughly 80 billion chickens alive each year supplying meat and eggs, the vast majority part of a global poultry industry. As a result, avian immunology been studied intensively for over 60 years, and it has become clear that a major genetic locus in chickens determining resistance to infectious disease and response to vaccines is the major histocompatibility complex (MHC). Compared to typical mammals, the chicken MHC is compact and simple, with only two classical class I genes. A dominantly-expressed class I gene, BF2, is the major ligand for cytotoxic T lymphocytes (CTLs), while the other locus, BF1, is much less well-expressed, lacking in some MHC haplotypes, and is a ligand for natural killer (NK) cells. Cell surface class I expression in neonatal chicks is far less than in adults, and one possibility is that BF2 is not well-expressed early in ontogeny. A precedent is found for amphibians: the single classical class I molecule is not expressed in tadpoles of Xenopus frogs, although non-polymorphic (and thus non-classical) class I molecules from the XNC locus are expressed, which are recognised for immune defence by non-canonical NKT lymphocytes. Indeed, three waves of different T cells are produced by the Xenopus thymus: in tadpoles, during metamorphosis and finally as adults. Three waves of thymic emigrants are also found for chickens, and reasoning by analogy, it may be that the waves of thymocytes and the expression of class I molecules during ontogeny of chickens are evolutionary relics. As well as scientific interest in the ontogeny of MHC class I expression and appearance of peripheral T cells, there are potential practical implications, given the importance of vaccination in ovo and in day-old chicks for the poultry industry.

mRNA Galsomes Vaccine Protects Budgerigars Against Virulent Chlamydia psittaci Challenge

BACKGROUND/OBJECTIVES

Chlamydia (C.) psittaci is an avian respiratory pathogen that regularly infects budgerigars (Melopsittacus undulatus) and is a known zoonosis. This study aimed to evaluate the efficacy of a nucleoside-modified mRNA vaccine formulated in lipid nanoparticles (LNPs), either with (mRNA Galsomes) or without (mRNA LNPs) the glycolipid antigen α-Galactosylceramide, in protecting budgerigars against C. psittaci genotype A infection.

METHODS

Three groups of eight budgerigars received two intramuscular vaccinations with PBS, mRNA LNPs or mRNA Galsomes, and were subsequently challenged via aerosol with the C. psittaci genotype A strain 90/1051. Vaccine efficacy was assessed over 14 days post challenge by monitoring clinical signs, macroscopic and microscopic lesions, pathogen excretion and chlamydial burden in organs. Antibody levels were evaluated at baseline, after vaccination and post challenge.

RESULTS

Both mRNA LNPs and mRNA Galsomes induced significant serum antibody responses post booster. Vaccination significantly reduced clinical signs, chlamydial burden in the lungs and macroscopic lesions in conjunctiva, conchae, lungs and thoracic airsacs, compared to controls. Additionally, mRNA Galsomes-treated birds showed a significantly reduced lung inflammation and fewer macroscopic lesions in abdominal airsacs and liver, compared to non-vaccinated animals. These animals also experienced a significantly lower chlamydial burden in the spleen, fewer clinical signs at day 11 and fewer fecal shedding at day 14 post challenge, compared to mRNA LNP-treated animals.

CONCLUSIONS

This study demonstrated that mRNA vaccination confers partial protection against C. psittaci in budgerigars, with mRNA Galsomes appearing to provide enhanced efficacy. However, the absence of species-specific reagents for assessing cellular immunity in Psittaciformes limits a comprehensive understanding of vaccine-induced protection. The development of psittacine-specific T cell markers and cytokine assays is necessary to further elucidate immune mechanisms and optimize vaccine formulations.

Different MHC class I cell surface expression levels in diverse chicken lines, associations with B blood group, and proposed relationship to antigen-binding repertoire

The Major Histocompatibility Complex (MHC) is a cluster of genes with primarily immune-related functions. The MHC class I genes are responsible for self- versus non-self-recognition and viral antigen presentation to T lymphocytes. The chicken MHC class I protein binds its cognate antigen(s) over a repertoire spectrum ranging from promiscuous (generalist) to fastidious (specialist). The MHC class I protein expression level at the cell surface is inversely related to the promiscuity of its peptide-binding repertoire. In our study, erythrocytes from 6 diverse and highly inbred lines of chickens, a closed broiler line, and a highly advanced intercross line were evaluated for MHC class I antigen expression level by flow cytometry using monoclonal antibodies to chicken MHC class I molecules. In chickens, the B blood group antigens include the MHC class I antigen expressed from the MHC. Thus, the B blood group has historically been used as a genetic marker for Marek's Disease virus response. Erythrocytes of the inbred lines were blood typed by serology. The B21 blood type is widely recognized as relatively resistant to Marek's disease and regarded as an MHC class I generalist with low MHC class I expression. The Spanish line, which types serologically as B21.1 (similar to B21), was the lowest MHC class I expressing line. The two sublines (B5.1 and B15.2) of the Fayoumi breed, which significantly differed in their MHC class I expression, also differ in response to multiple pathogens. These defined genetic lines of chickens, with distinct MHC class I expression levels, provide an excellent platform to further interrogate the hypothesis of high or low MHC class I expression (antigenic specialists or generalists, respectively) determining diverse responses to pathogens.

Comparative Analysis of Runs of Homozygosity Islands in Indigenous and Commercial Chickens Revealed Candidate Loci for Disease Resistance and Production Traits

Runs of homozygosity (ROH) are contiguous stretches of identical genomic regions inherited from both parents. Assessment of ROH in livestock species contributes significantly to our understanding of genetic health, population genetic structure, selective pressure and conservation efforts. In this study, whole genome re-sequencing data from 140 birds of 10 Iranian indigenous chicken ecotypes, 3 commercial chicken breeds and 1 red junglefowl (RJF) population were used to investigate their population genetic structure, ROH characteristics (length and frequency) and genomic inbreeding coefficients (FROH). Additionally, we examined ROH islands for selection footprints in the indigenous chicken populations. Our results revealed distinct genetic backgrounds, among which the White Leghorn breed exhibited the greatest genetic distance from other populations, while the gamecock populations formed a separate cluster. We observed significant differences in ROH characteristics, in which the commercial breeds showed a higher number of ROH compared to indigenous chickens and red junglefowls. Short ROH ranging from 0.1 to 1 Mb were dominant among the populations. The Arian line had the highest mean length of ROH, while the White Leghorn breed showed the highest number of ROH. Among indigenous chickens, the Lari-Afghani ecotype exhibited the highest FROH, but the Sari inherited the richest genetic diversity. Interestingly, GGA16 carried no ROH in the red junglefowls, whereas GGA22 had the highest FROH across all populations, except in the Isfahan ecotype. We also identified ROH islands associated with genetic adaptations in indigenous ecotypes. These islands harboured immune-related genes contributing to disease resistance (TLR2, TICAM1, IL22RA1, NOS2, CCL20 and IFNLR1), heat tolerance and oxidative stress response (NFKB1, HSF4, OSGIN1 and BDNF), and muscle development, lipid metabolism and reproduction (MEOX2, CEBPB, CDS2 and GnRH-I). Overall, this study highlights the genetic potential of indigenous chickens to survive and adapt to their respective environments.

Mapping quantitative trait loci regions associated with Marek's disease on chicken autosomes by means of selective DNA pooling

Marek's Disease (MD), which can result in neurological damage and tumour formation, has large effects on the economy and animal welfare of the poultry industry worldwide. Previously, we mapped autosomal MD QTL regions (QTLRs) by individual genotyping of an F6 population from a full-sib advanced intercross line. We further mapped MD QTLRs on the chicken Z chromosome (GGZ) using the same F6 population, and by selective DNA pooling (SDP) of 8 elite egg production lines. Here we used SDP of the same pools used on GGZ to map autosomal MD QTLRs. Thirty-seven QTLRs were found. Seven of the QTLRs were tested by all sires from the same 8 lines, individually genotyped for QTLR markers. Five of the tested QTLRs were confirmed. Linkage disequilibrium (LD) was calculated for all QTLR markers on the same chromosome, and complex LD blocks were found. Distribution of P and LD values were used to assess the QTLR causative elements. Allele substitution effects were calculated based on both pooled SNP microarray genotypes, and individual genotypes of QTLRs markers. Substantial allele effect and contribution to the phenotypic and genotypic variation were obtained. The results explain part of the MD response, and provide targets for mitigating MD.

Two different complement Factor B (Bf) alleles of the orangutan major histocompatibility complex (MHC) are also conserved in chimpanzee and humans showing importance in primate immunity

BACKGROUND

Major Human Histocompatibility complex (MHC or HLA in humans) has been associated to autoimmune diseases. However, only statistical phenomenological and no pathogenetic description has been reached after decades. This shows that MHC single locus association studies are probably useless for HLA/diseases association. Extended HLA (class I and class II genes) haplotypes should also be studied conjointly with class III or complement alleles (complotypes). Complotypes in humans are defined as alleles belonging to C2, C4 and Bf (Factor B) genes/proteins (class III). Also, the placing of MHC class I and class II genes close together with complement genes from at least birds to humans shows existence of a strong selection to gather conjointly these loci that fight microbes, help self-maintenance and avoid autoimmunity. In this paper we aim to study Bf alleles in primates in order to rise again interest to study the role of Bf alleles together with other MHC genes in their physiopathology and evolution.

METHODS

Orangutan (Pongo pygmaeus, Popy) cell lines RNA from 6 different individuals were retrotranscribed, PCR amplified, cloned and DNA sequenced in order to study Bf alleles.

RESULTS

A Bf allele identical to that found in chimpanzee (Patr-Bf*A01) and human (rs641153) was found in two of the six studied orangutans: Popy-Bf*A01 and Popy-Bf*A02. This polymorphism is placed in Factor B codon 32 that defines BF*S and Bf*F proteins in man and produce Leu instead of Arg (Bf*S) or Gln (Bf*F). In addition, each new orangutan allele present synonymous differences with each other at codon 25: Popy-Bf*A01 shows ACG while Popy-Bf*A02 bears ACA, both codifying for Thr.

CONCLUSIONS

The selection for about 15 million years (time gap of evolutionary appearance between orangutan and hominids) shows the importance of this particular allele conservation in immune and self defense in primates. The complotypes (Bf,C2 and C4 loci) alleles together with other MHC class I and Cass II loci alleles are often transmitted in block to the germinal line: this indicates that all specific alleles from the MHC different loci may work together to accomplish MHC functions. All MHC loci alleles should be studied together to unveil their physiopathology and also maintenance of specific alleles (like the one described in this paper) for so long time in evolution should be further studied in Bf and the other neighbouring complement loci (C2 and C4).

Association of Major Histocompatibility Complex Polymorphism With Acute Phase Response in Broiler Chicken

BACKGROUND

Stress associated with changes in host immunity occurs in response to altered environmental conditions, endogenous imbalances, infectious agents and harmful stimuli. The importance of genetic diversity in chickens has increased due to individual immune differences towards resistance and susceptibility to various stimuli.

OBJECTIVES

This study aimed to investigate the association of major histocompatibility complex (MHC) polymorphism with acute phase response (APR) in Ross 308 broiler chickens.

METHODS

The allelic diversity of the LEI0258 microsatellite marker was determined in 120 Ross broilers. In addition, acute phase proteins (APPs), including serum amyloid A (SAA) and alpha-1-acid glycoprotein (AGP), were analysed as markers of the APR. Furthermore, leukocyte count and the heterophil/lymphocyte ratio (H/L ratio) were examined. The antibody response to the Newcastle disease vaccine (NDV) was also measured to assess humoral mediated immunity. Lastly, the correlation between immune responses and MHC alleles was investigated to identify the most effective alleles in a stress-related situation.

RESULTS

A total of six alleles, ranging from 195 to 448 bp, were identified. Association study revealed a significant influence of MHC alleles on APPs in Ross population (p < 0.05). Notably, Allele 448 had a significant correlation with SAA concentration and the H/L ratio. Allele 207 displayed a positive association with AGP concentration, whereas Allele 195 showed a negative association. Furthermore, a significant association was observed between Allele 448 and basopenia, as well as between Allele 195 and monocytosis.

CONCLUSIONS

Results confirmed the significance of MHC as a candidate gene marker for immune responses, which supports its use for vaccine design, genetic improvement of disease-resistant traits and resource conservation in commercial broiler chickens.

The RHCE gene encodes the chicken blood system I

BACKGROUND

There are 13 known chicken blood systems, which were originally detected by agglutination of red blood cells by specific alloantisera. The genomic region or specific gene responsible has been identified for four of these systems (A, B, D and E). We determined the identity of the gene responsible for the chicken blood system I, using DNA from multiple birds with known chicken I blood system serology, 600K and 54K single nucleotide polymorphism (SNP) data, and lowpass sequence information.

RESULTS

The gene responsible for the chicken I blood system was identified as RHCE, which is also one of the genes responsible for the highly polymorphic human Rh blood group locus, for which maternal/fetal antigenic differences can result in fetal hemolytic anemia with fetal mortality. We identified 17 unique RHCE haplotypes in the chicken, with six haplotypes corresponding to known I system serological alleles. We also detected deletions in the RHCE gene that encompass more than 6000 bp and that are predicted to remove its last seven exons.

CONCLUSIONS

RHCE is the gene responsible for the chicken I blood system. This is the fifth chicken blood system for which the responsible gene and gene variants are known. With rapid DNA-based testing now available, the impact of I blood system variation on response against disease, general immune function, and animal production can be investigated in greater detail.

Major histocompatibility complex genes exhibit a potential immunological role in mixed Eimeria-infected broiler cecum analyzed using RNA sequencing

OBJECTIVE

This study was conducted to investigate the differential expression of the major histocompatibility complex (MHC) gene region in Eimeria-infected broiler.

METHODS

We profiled gene expression of Eimeria-infected and uninfected ceca of broilers sampled at 4, 7, and 21 days post-infection (dpi) using RNA sequencing. Differentially expressed genes (DEGs) between two sample groups were identified at each time point. DEGs located on chicken chromosome 16 were used for further analysis. Kyoto encyclopedia of genes and genomes (KEGG) pathway analysis was conducted for the functional annotation of DEGs.

RESULTS

Fourteen significant (false discovery rate <0.1) DEGs were identified at 4 and 7 dpi and categorized into three groups: MHC-Y class I genes, MHC-B region genes, and non-MHC genes. In Eimeria-infected broilers, MHC-Y class I genes were upregulated at 4 dpi but downregulated at 7 dpi. This result implies that MHC-Y class I genes initially activated an immune response, which was then suppressed by Eimeria. Of the MHC-B region genes, the DMB1 gene was upregulated, and TAP-related genes significantly implemented antigen processing for MHC class I at 4 dpi, which was supported by KEGG pathway analysis.

CONCLUSION

This study is the first to investigate MHC gene responses to coccidia infection in chickens using RNA sequencing. MHC-B and MHC-Y genes showed their immune responses in reaction to Eimeria infection. These findings are valuable for understanding chicken MHC gene function.

Proteome and Peptidome Changes and Zn Concentration in Chicken after In Ovo Stimulation with a Multi-Strain Probiotic and Zn-Gly Chelate: Preliminary Research

The aim of the study was to determine differences in the proteome and peptidome and zinc concentrations in the serum and tissues of chickens supplemented with a multi-strain probiotic and/or zinc glycine chelate in ovo. A total of 1400 fertilized broiler eggs (Ross × Ross 708) were divided into four groups: a control and experimental groups injected with a multi-strain probiotic, with zinc glycine chelate, and with the multi-strain probiotic and zinc glycine chelate. The proteome and peptidome were analyzed using SDS-PAGE and MALDI-TOF MS, and the zinc concentration was determined by flame atomic absorption spectrometry. We showed that in ovo supplementation with zinc glycine chelate increased the Zn concentration in the serum and yolk sac at 12 h post-hatch. The results of SDS-PAGE and western blot confirmed the presence of Cu/Zn SOD in the liver and in the small and large intestines at 12 h and at 7 days after hatching in all groups. Analysis of the MALDI-TOF MS spectra of chicken tissues showed in all experimental groups the expression of proteins and peptides that regulate immune response, metabolic processes, growth, development, and reproduction.

Immunoglobulin-like receptors in chickens: identification, functional characterization, and renaming to cluster homolog of immunoglobulin-like receptors

The cluster homolog of immunoglobulin-like receptors (CHIRs), previously known as the "chicken homolog of immunogloublin-like receptors," represents is a large group of transmembrane glycoproteins that direct the immune response. However, the full repertoire of putatively activating, inhibitory, or dual function CHIRA, CHIRB, and CHIRAB on chickens' immune responses is poorly understood. Herein, the study objective was to determine the genes encoding CHIR proteins and predict their function by searching canonical protein structure. A bioinformatics pipeline based on previous work was employed to search for the CHIRs from the newly updated broiler and layer genomes. The categorization into CHIRA, CHIRB, and CHIRAB types was assigned through motif searches, multiple sequence alignment, and phylogeny. In total, 150 protein-encoding genes on Chromosome 31 were identified as CHIRs. Gene members of each functional group (CHIRA, CHIRB, CHIRAB) were classified in accordance with previously recognized proteins. The genes were renamed to "cluster homolog of immunoglobulin-like receptors" (CHIRs) to allow for the naming of orthologous genes in other avian species. Additionally, expression analysis of the classified CHIRs across various reinforces their importance as immune regulators and activation in inflammatory tissues. Furthermore, over 1,000 diverse and rare CHIRs variants associated with differential Marek's disease response (P < 0.05) emphasize the impact of CHIRs on shaping avian immune responses in diverse contexts. The practical applications of these findings encompass advancing immunology, improving poultry health management, optimizing breeding programs for disease resistance, and enhancing overall animal health through a deeper understanding of the roles and functions of CHIRA, CHIRB, and CHIRAB types in avian immune responses.

The genome of a globally invasive passerine, the common myna, Acridotheres tristis

In an era of global climate change, biodiversity conservation is receiving increased attention. Conservation efforts are greatly aided by genetic tools and approaches, which seek to understand patterns of genetic diversity and how they impact species health and their ability to persist under future climate regimes. Invasive species offer vital model systems in which to investigate questions regarding adaptive potential, with a particular focus on how changes in genetic diversity and effective population size interact with novel selection regimes. The common myna (Acridotheres tristis) is a globally invasive passerine and is an excellent model species for research both into the persistence of low-diversity populations and the mechanisms of biological invasion. To underpin research on the invasion genetics of this species, we present the genome assembly of the common myna. We describe the genomic landscape of this species, including genome wide allelic diversity, methylation, repeats, and recombination rate, as well as an examination of gene family evolution. Finally, we use demographic analysis to identify that some native regions underwent a dramatic population increase between the two most recent periods of glaciation, and reveal artefactual impacts of genetic bottlenecks on demographic analysis.

A chromosome-level genome assembly for the Silkie chicken resolves complete sequences for key chicken metabolic, reproductive, and immunity genes

A set of high-quality pan-genomes would help identify important genes that are still hidden/incomplete in bird reference genomes. In an attempt to address these issues, we have assembled a de novo chromosome-level reference genome of the Silkie (Gallus gallus domesticus), which is an important avian model for unique traits, like fibromelanosis, with unclear genetic foundation. This Silkie genome includes the complete genomic sequences of well-known, but unresolved, evolutionarily, endocrinologically, and immunologically important genes, including leptin, ovocleidin-17, and tumor-necrosis factor-α. The gap-less and manually annotated MHC (major histocompatibility complex) region possesses 38 recently identified genes, with differentially regulated genes recovered in response to pathogen challenges. We also provide whole-genome methylation and genetic variation maps, and resolve a complex genetic region that may contribute to fibromelanosis in these animals. Finally, we experimentally show leptin binding to the identified leptin receptor in chicken, confirming an active leptin ligand-receptor system. The Silkie genome assembly not only provides a rich data resource for avian genome studies, but also lays a foundation for further functional validation of resolved genes.

A critical assessment of the cellular defences of the avian respiratory system: are birds in general and poultry in particular relatively more susceptible to pulmonary infections/afflictions?

In commercial poultry farming, respiratory diseases cause high morbidities and mortalities, begetting colossal economic losses. Without empirical evidence, early observations led to the supposition that birds in general, and poultry in particular, have weak innate and adaptive pulmonary defences and are therefore highly susceptible to injury by pathogens. Recent findings have, however, shown that birds possess notably efficient pulmonary defences that include: (i) a structurally complex three-tiered airway arrangement with aerodynamically intricate air-flow dynamics that provide efficient filtration of inhaled air; (ii) a specialised airway mucosal lining that comprises air-filtering (ciliated) cells and various resident phagocytic cells such as surface and tissue macrophages, dendritic cells and lymphocytes; (iii) an exceptionally efficient mucociliary escalator system that efficiently removes trapped foreign agents; (iv) phagocytotic atrial and infundibular epithelial cells; (v) phagocytically competent surface macrophages that destroy pathogens and injurious particulates; (vi) pulmonary intravascular macrophages that protect the lung from the vascular side; and (vii) proficiently phagocytic pulmonary extravasated erythrocytes. Additionally, the avian respiratory system rapidly translocates phagocytic cells onto the respiratory surface, ostensibly from the subepithelial space and the circulatory system: the mobilised cells complement the surface macrophages in destroying foreign agents. Further studies are needed to determine whether the posited weak defence of the avian respiratory system is a global avian feature or is exclusive to poultry. This review argues that any inadequacies of pulmonary defences in poultry may have derived from exacting genetic manipulation(s) for traits such as rapid weight gain from efficient conversion of food into meat and eggs and the harsh environmental conditions and severe husbandry operations in modern poultry farming. To reduce pulmonary diseases and their severity, greater effort must be directed at establishment of optimal poultry housing conditions and use of more humane husbandry practices.

Major histocompatibility complex complement (MHC) Bf alleles show trans species evolution between man and chimpanzee

HLA and disease studies by using single allele statistics have been fruitless during the last 40 years for explaining association pathogenesis of the associated diseases.Other approaches are necessary to untangle this puzzle. We aim to revisit complement alleleism in humans and primates for both studying MHC and disease association to complotypes and extended MHC haplotypes in order to also explain the positive directional selection of maintaining immune response genes (complement, MHC adaptive and MHC non-specific genes) that keeps these three type of genes together in a short chromosome stretch (MHC) for million years. These genes may be linked to conjointly avoid microbes attack and autoimmunity. In the present paper, it is obtained a new Bf chimpanzee allele, provisionaly named Patr-Bf*A:01,that differs from other Bf alleles by having CTG at eleventh codon of exon 2 in order to start the newly suggested methodology and explain functional and evolutionary MHC obscure aspects. Exons 1 to 6 of Ba fragment of Bf gene were obtained from chimpanzee. This new chimpanzee Factor B allele (Patr-Bf*A:01) is to be identical to a infrequent human Bf allele (SNP rs641153); it stresses the strong evolutive pressure upon certain alleles that are trans specific. It also may apply to MHC extended haplotipes which may conjointly act to start an adequate immune response. It is the first time that a complement MHC class III allele is described to undergo trans species evolution,in contrast to class I and class II alleles which had already been reported . Allelism of complement factors are again proposed for studying MHC complement genes, complotypes, and extended MHC haplotypes which may be more informative that single MHC marker studies.

Novel MHC BLB2 gene polymorphism and its association with IgY concentration and Newcastle disease antibody titer in IPB-D2 chickens

This study aimed to identify the polymorphism of the B Locus Beta 2 (BLB2) gene and its association with immunoglobulin Y (IgY) concentration and Newcastle disease (ND) antibody titer; we analyzed BLB2 gene expression in different categories of ND antibody titers in IPB-D2 chickens. The total sample used was 100 IPB-D2 chickens. Blood samples were collected at 21 weeks old for an ELISA (enzyme-linked immunoassay) test, an HI (hemagglutination inhibition) test, and genotyping. The method for BLB2 polymorphism was Sanger sequencing. Analysis of BLB2 gene expression was performed using the cecal tonsil tissue of IPB-D2 chickens. Polymorphism data were analyzed using SNPstats and DNAsp (DNA Sequence Polymorphism) software. The association of the single-nucleotide polymorphisms (SNPs) with IgY concentration and ND antibody titer was analyzed using SAS software (version 9.2). The genotype mean values were compared by means of a T test. The relative mRNA expression analysis was performed using a quantitative real-time polymerase chain reaction (qRT-PCR). The results showed that 13 SNPs were found in exon 2 and exon 3 in the BLB2 gene. As many as 4 out of the 13 SNPs were associated with IgY concentration. As many as 9 out the 13 SNPs may have changed amino acids. The Δ Ct value showed that the expression of the BLB2 gene in IPB-D2 chickens with high ND antibody titers is higher than IPB-D2 chickens with low ND antibody titers. In conclusion, the AA genotype of g.458 T >  A was associated with high IgY concentrations, and the BLB2 gene presented with a high expression in IPB-D2 chickens with high ND antibody titers.

Discovery of novel MHC-B haplotypes in Chantecler chickens

The major histocompatibility complex (MHC) is a highly polymorphic cluster of genes which contribute to immune response. Located on chromosome 16, the chicken MHC has great influence over disease resistance and susceptibility. Through the use of a high-density SNP panel which encompasses the MHC-B region, haplotypes can be easily identified. This study aims to use an MHC-B SNP panel to evaluate the MHC-B variability in the Chantecler breed. This breed is native to Quebec, Canada, and is a dual-purpose breed known for its strong resistance to extreme cold temperatures. The Chantecler breed faced a near extinction event in the 1970s, which most likely resulted in a genetic bottleneck and loss of diversity. Despite this, SNP haplotype diversity was observed among 4 Chantecler populations. A total of 8 haplotypes were observed. Of these haplotypes, 6 were previously defined in other breeds, and the other 2 were unique to the Chantecler. Within the populations, the number of haplotypes ranged from 4 to 7, with 3 haplotypes, including the novel BSNP-Chant01, being present in all the groups. This study shows existence of reasonable diversity in the MHC-B region of the Chantecler breed and our results further contribute to understanding the variability of this region in chickens.

A Wider and Deeper Peptide-Binding Groove for the Class I Molecules from B15 Compared with B19 Chickens Correlates with Relative Resistance to Marek's Disease

The chicken MHC is known to confer decisive resistance or susceptibility to various economically important pathogens, including the iconic oncogenic herpesvirus that causes Marek's disease (MD). Only one classical class I gene, BF2, is expressed at a high level in chickens, so it was relatively easy to discern a hierarchy from well-expressed thermostable fastidious specialist alleles to promiscuous generalist alleles that are less stable and expressed less on the cell surface. The class I molecule BF2*1901 is better expressed and more thermostable than the closely related BF2*1501, but the peptide motif was not simpler as expected. In this study, we confirm for newly developed chicken lines that the chicken MHC haplotype B15 confers resistance to MD compared with B19. Using gas phase sequencing and immunopeptidomics, we find that BF2*1901 binds a greater variety of amino acids in some anchor positions than does BF2*1501. However, by x-ray crystallography, we find that the peptide-binding groove of BF2*1901 is narrower and shallower. Although the self-peptides that bound to BF2*1901 may appear more various than those of BF2*1501, the structures show that the wider and deeper peptide-binding groove of BF2*1501 allows stronger binding and thus more peptides overall, correlating with the expected hierarchies for expression level, thermostability, and MD resistance. Our study provides a reasonable explanation for greater promiscuity for BF2*1501 compared with BF2*1901, corresponding to the difference in resistance to MD.

CD99 and the Chicken Alloantigen D Blood System

The chicken D blood system is one of 13 alloantigen systems found on chicken red blood cells. Classical recombinant studies located the D blood system on chicken chromosome 1, but the candidate gene was unknown. Multiple resources were utilized to identify the chicken D system candidate gene, including genome sequence information from both research and elite egg production lines for which D system alloantigen alleles were reported, and DNA from both pedigree and non-pedigree samples with known D alleles. Genome-wide association analyses using a 600 K or a 54 K SNP chip plus DNA from independent samples identified a strong peak on chicken chromosome 1 at 125-131 Mb (GRCg6a). Cell surface expression and the presence of exonic non-synonymous SNP were used to identify the candidate gene. The chicken CD99 gene showed the co-segregation of SNP-defined haplotypes and serologically defined D blood system alleles. The CD99 protein mediates multiple cellular processes including leukocyte migration, T-cell adhesion, and transmembrane protein transport, affecting peripheral immune responses. The corresponding human gene is found syntenic to the pseudoautosomal region 1 of human X and Y chromosomes. Phylogenetic analyses show that CD99 has a paralog, XG, that arose by duplication in the last common ancestor of the amniotes.

Mass Spectrometry Defines Lysophospholipids as Ligands for Chicken MHCY Class I Molecules

Chicken (Gallus gallus) MHCY class I molecules are highly polymorphic yet substantially different from polymorphic MHC class I molecules that bind peptide Ags. The binding grooves in MHCY class I molecules are hydrophobic and too narrow to accommodate peptides. An earlier structural study suggested that ligands for MHCY class I might be lipids, but the contents of the groove were not clearly identified. In this study, lysophospholipids have been identified by mass spectrometry as bound in two MHCY class I isoforms that differ substantially in sequence. The two isoforms, YF1*7.1 and YF1*RJF34, differ by 35 aa in the α1 and α2 domains that form the MHC class I ligand binding groove. Lyso-phosphatidylethanolamine (lyso-PE) 18:1 was the dominant lipid identified in YF1*7.1 and YF1*RJF34 expressed as recombinant molecules and renatured with β2-microglobulin in the presence of a total lipid extract from Escherichia coli. Less frequently detected were lyso-PE 17:1, lyso-PE 16:1, and lysophosphatidylglycerols 17:1 and 16:0. These data provide evidence that lysophospholipids are candidate ligands for MHCY class I molecules. Finding that MHCY class I isoforms differing substantially in sequence bind the same array of lysophospholipids indicates that the amino acid polymorphism that distinguishes MHCY class I molecules is not key in defining ligand specificity. The polymorphic positions lie mostly away from the binding groove and might define specificity in interactions of MHCY class I molecules with receptors that are presently unidentified. MHCY class I molecules are distinctive in bound ligand and in display of polymorphic residues.

Sex Differences in Response to Marek's Disease: Mapping Quantitative Trait Loci Regions (QTLRs) to the Z Chromosome

Marek's Disease (MD) has a significant impact on both the global poultry economy and animal welfare. The disease pathology can include neurological damage and tumour formation. Sexual dimorphism in immunity and known higher susceptibility of females to MD makes the chicken Z chromosome (GGZ) a particularly attractive target to study the chicken MD response. Previously, we used a Hy-Line F₆ population from a full-sib advanced intercross line to map MD QTL regions (QTLRs) on all chicken autosomes. Here, we mapped MD QTLRs on GGZ in the previously utilized F₆ population with individual genotypes and phenotypes, and in eight elite commercial egg production lines with daughter-tested sires and selective DNA pooling (SDP). Four MD QTLRs were found from each analysis. Some of these QTLRs overlap regions from previous reports. All QTLRs were tested by individuals from the same eight lines used in the SDP and genotyped with markers located within and around the QTLRs. All QTLRs were confirmed. The results exemplify the complexity of MD resistance in chickens and the complex distribution of p-values and Linkage Disequilibrium (LD) pattern and their effect on localization of the causative elements. Considering the fragments and interdigitated LD blocks while using LD to aid localization of causative elements, one must look beyond the non-significant markers, for possible distant markers and blocks in high LD with the significant block. The QTLRs found here may explain at least part of the gender differences in MD tolerance, and provide targets for mitigating the effects of MD.

The Gallus gallus RJF reference genome reveals an MHCY haplotype organized in gene blocks that contain 107 loci including 45 specialized, polymorphic MHC class I loci, 41 C-type lectin-like loci, and other loci amid hundreds of transposable elements

MHCY is a second major histocompatibility complex-like gene region in chickens originally identified by the presence of major histocompatibility complex class I-like and class II-like gene sequences. Up to now, the MHCY gene region has been poorly represented in genomic sequence data. A high density of repetitive sequence and multiple members of several gene families prevented the accurate assembly of short-read sequence data for MHCY. Identified here by single-molecule real-time sequencing sequencing of BAC clones for the Gallus gallus Red Jungle Fowl reference genome are 107 MHCY region genes (45 major histocompatibility complex class I-like, 41 c-type-lectin-like, 8 major histocompatibility complex class IIβ, 8 LENG9-like, 4 zinc finger protein loci, and a single only zinc finger-like locus) located amid hundreds of retroelements within 4 contigs representing the region. Sequences obtained for nearby ribosomal RNA genes have allowed MHCY to be precisely mapped with respect to the nucleolar organizer region. Gene sequences provide insights into the unusual structure of the MHCY class I molecules. The MHCY class I loci are polymorphic and group into 22 types based on predicted amino acid sequences. Some MHCY class I loci are full-length major histocompatibility complex class I genes. Others with altered gene structure are considered gene candidates. The amino acid side chains at many of the polymorphic positions in MHCY class I are directed away rather than into the antigen-binding groove as is typical of peptide-binding major histocompatibility complex class I molecules. Identical and nearly identical blocks of genomic sequence contribute to the observed multiplicity of identical MHCY genes and the large size (&gt;639 kb) of the Red Jungle Fowl MHCY haplotype. Multiple points of hybridization observed in fluorescence in situ hybridization suggest that the Red Jungle Fowl MHCY haplotype is made up of linked, but physically separated genomic segments. The unusual gene content, the evidence of highly similar duplicated segments, and additional evidence of variation in haplotype size distinguish polymorphic MHCY from classical polymorphic major histocompatibility complex regions.

Transcript- and annotation-guided genome assembly of the European starling

The European starling, Sturnus vulgaris, is an ecologically significant, globally invasive avian species that is also suffering from a major decline in its native range. Here, we present the genome assembly and long-read transcriptome of an Australian-sourced European starling (S. vulgaris vAU), and a second, North American, short-read genome assembly (S. vulgaris vNA), as complementary reference genomes for population genetic and evolutionary characterization. S. vulgaris vAU combined 10× genomics linked-reads, low-coverage Nanopore sequencing, and PacBio Iso-Seq full-length transcript scaffolding to generate a 1050 Mb assembly on 6222 scaffolds (7.6 Mb scaffold N50, 94.6% busco completeness). Further scaffolding against the high-quality zebra finch (Taeniopygia guttata) genome assigned 98.6% of the assembly to 32 putative nuclear chromosome scaffolds. Species-specific transcript mapping and gene annotation revealed good gene-level assembly and high functional completeness. Using S. vulgaris vAU, we demonstrate how the multifunctional use of PacBio Iso-Seq transcript data and complementary homology-based annotation of sequential assembly steps (assessed using a new tool, saaga) can be used to assess, inform, and validate assembly workflow decisions. We also highlight some counterintuitive behaviour in traditional busco metrics, and present buscomp, a complementary tool for assembly comparison designed to be robust to differences in assembly size and base-calling quality. This work expands our knowledge of avian genomes and the available toolkit for assessing and improving genome quality. The new genomic resources presented will facilitate further global genomic and transcriptomic analysis on this ecologically important species.

Advances on genetic and genomic studies of ALV resistance

Avian leukosis (AL) is a general term for a variety of neoplastic diseases in avian caused by avian leukosis virus (ALV). No vaccine or drug is currently available for the disease. Therefore, the disease can result in severe economic losses in poultry flocks. Increasing the resistance of poultry to ALV may be one effective strategy. In this review, we provide an overview of the roles of genes associated with ALV infection in the poultry genome, including endogenous retroviruses, virus receptors, interferon-stimulated genes, and other immune-related genes. Furthermore, some methods and techniques that can improve ALV resistance in poultry are discussed. The objectives are willing to provide some valuable references for disease resistance breeding in poultry.

The Chicken A and E Blood Systems Arise from Genetic Variation in and around the Regulators of Complement Activation Region

The tightly linked A and E blood alloantigen systems are 2 of 13 blood systems identified in chickens. Reported herein are studies showing that the genes encoding A and E alloantigens map within or near to the chicken regulator of complement activation (RCA) gene cluster, a region syntenic with the human RCA. Genome-wide association studies, sequence analysis, and sequence-derived single-nucleotide polymorphism information for known A and/or E system alleles show that the most likely candidate gene for the A blood system is C4BPM gene (complement component 4 binding protein, membrane). Cosegregation of single-nucleotide polymorphism–defined C4BPM haplotypes and blood system A alleles defined by alloantisera provide a link between chicken blood system A and C4BPM. The best match for the E blood system is the avian equivalent of FCAMR (Fc fragment of IgA and IgM receptor). C4BPM is located within the chicken RCA on chicken microchromosome 26 and is separated from FCAMR by 89 kbp. The genetic variation observed at C4BPM and FCAMR could affect the chicken complement system and differentially guide immune responses to infectious diseases.

Marek's disease virus-specific T cells proliferate, express antiviral cytokines but have impaired degranulation response

The major histocompatibility complex (MHC) haplotype is one of the major determinants of genetic resistance and susceptibility of chickens to Marek's disease (MD) which is caused by an oncogenic herpesvirus; Marek's disease virus (MDV). To determine differential functional abilities of T cells associated with resistance and susceptibility to MD, we identified immunodominant CD4+TCRvβ1 T cell epitopes within the pp38 antigen of MDV in B19 and B21 MHC haplotype chickens using an ex vivo ELISPOT assay for chicken IFN-gamma. These novel pp38 peptides were used to characterize differential functional abilities of T cells as associated with resistance and susceptibility to MD. The results demonstrated an upregulation of cytokines (IL-2, IL-4, IL-10) and lymphocyte lysis-related genes (perforin and granzyme B) in an antigen specific manner using RT-PCR. In the MD-resistant chickens (B21 MHC haplotype), antigen-specific and non-specific response was highly skewed towards Th2 response as defined by higher levels of IL-4 expression as well as lymphocyte lysis-related genes compared to that in the MD-susceptible chicken line (B19 MHC haplotype). Using CD107a degranulation assay, the results showed that MDV infection impairs cytotoxic function of T cells regardless of their genetic background. Taken together, the data demonstrate an association between type of T cell response to pp38 and resistance to the disease and will shed light on our understanding of immune response to this oncogenic herpesvirus and failure to induce sterile immunity.

Evolution and molecular interactions of major histocompatibility complex (MHC)-G, -E and -F genes

Classical HLA (Human Leukocyte Antigen) is the Major Histocompatibility Complex (MHC) in man. HLA genes and disease association has been studied at least since 1967 and no firm pathogenic mechanisms have been established yet. HLA-G immune modulation gene (and also -E and -F) are starting the same arduous way: statistics and allele association are the trending subjects with the same few results obtained by HLA classical genes, i.e., no pathogenesis may be discovered after many years of a great amount of researchers' effort. Thus, we believe that it is necessary to follow different research methodologies: (1) to approach this problem, based on how evolution has worked maintaining together a cluster of immune-related genes (the MHC) in a relatively short chromosome area since amniotes to human at least, i.e., immune regulatory genes (MHC-G, -E and -F), adaptive immune classical class I and II genes, non-adaptive immune genes like (C2, C4 and Bf) (2); in addition to using new in vitro models which explain pathogenetics of HLA and disease associations. In fact, this evolution may be quite reliably studied during about 40 million years by analyzing the evolution of MHC-G, -E, -F, and their receptors (KIR-killer-cell immunoglobulin-like receptor, NKG2-natural killer group 2-, or TCR-T-cell receptor-among others) in the primate evolutionary lineage, where orthology of these molecules is apparently established, although cladistic studies show that MHC-G and MHC-B genes are the ancestral class I genes, and that New World apes MHC-G is paralogous and not orthologous to all other apes and man MHC-G genes. In the present review, we outline past and possible future research topics: co-evolution of adaptive MHC classical (class I and II), non-adaptive (i.e., complement) and modulation (i.e., non-classical class I) immune genes may imply that the study of full or part of MHC haplotypes involving several loci/alleles instead of single alleles is important for uncovering HLA and disease pathogenesis. It would mainly apply to starting research on HLA-G extended haplotypes and disease association and not only using single HLA-G genetic markers.

New vistas unfold: Chicken MHC molecules reveal unexpected ways to present peptides to the immune system

The functions of a wide variety of molecules with structures similar to the classical class I and class II molecules encoded by the major histocompatibility complex (MHC) have been studied by biochemical and structural studies over decades, with many aspects for humans and mice now enshrined in textbooks as dogma. However, there is much variation of the MHC and MHC molecules among the other jawed vertebrates, understood in the most detail for the domestic chicken. Among the many unexpected features in chickens is the co-evolution between polymorphic TAP and tapasin genes with a dominantly-expressed class I gene based on a different genomic arrangement compared to typical mammals. Another important discovery was the hierarchy of class I alleles for a suite of properties including size of peptide repertoire, stability and cell surface expression level, which is also found in humans although not as extreme, and which led to the concept of generalists and specialists in response to infectious pathogens. Structural studies of chicken class I molecules have provided molecular explanations for the differences in peptide binding compared to typical mammals. These unexpected phenomena include the stringent binding with three anchor residues and acidic residues at the peptide C-terminus for fastidious alleles, and the remodelling binding sites, relaxed binding of anchor residues in broad hydrophobic pockets and extension at the peptide C-terminus for promiscuous alleles. The first few studies for chicken class II molecules have already uncovered unanticipated structural features, including an allele that binds peptides by a decamer core. It seems likely that the understanding of how MHC molecules bind and present peptides to lymphocytes will broaden considerably with further unexpected discoveries through biochemical and structural studies for chickens and other non-mammalian vertebrates.

Caecal microbiota composition of experimental inbred MHC-B lines infected with IBV differs according to genetics and vaccination

Interactions between the gut microbiota and the immune system may be involved in vaccine and infection responses. In the present study, we studied the interactions between caecal microbiota composition and parameters describing the immune response in six experimental inbred chicken lines harboring different MHC haplotypes. Animals were challenge-infected with the infectious bronchitis virus (IBV), and half of them were previously vaccinated against this pathogen. We explored to what extent the gut microbiota composition and the genetic line could be related to the immune response, evaluated through flow cytometry. To do so, we characterized the caecal bacterial communities with a 16S rRNA gene amplicon sequencing approach performed one week after the IBV infectious challenge. We observed significant effects of both the vaccination and the genetic line on the microbiota after the challenge infection with IBV, with a lower bacterial richness in vaccinated chickens. We also observed dissimilar caecal community profiles among the different lines, and between the vaccinated and non-vaccinated animals. The effect of vaccination was similar in all the lines, with a reduced abundance of OTU from the Ruminococcacea UCG-014 and Faecalibacterium genera, and an increased abundance of OTU from the Eisenbergiella genus. The main association between the caecal microbiota and the immune phenotypes involved TCR_ϒδ expression on TCR_ϒδ⁺ T cells. This phenotype was negatively associated with OTU from the Escherichia-Shigella genus that were also less abundant in the lines with the highest responses to the vaccine. We proved that the caecal microbiota composition is associated with the IBV vaccine response level in inbred chicken lines, and that the TCR_ϒδ⁺ T cells (judged by TCR_ϒδ expression) may be an important component involved in this interaction, especially with bacteria from the Escherichia-Shigella genus. We hypothesized that bacteria from the Escherichia-Shigella genus increased the systemic level of bacterial lipid antigens, which subsequently mitigated poultry γδ T cells.

The Diverse Major Histocompatibility Complex Haplotypes of a Common Commercial Chicken Line and Their Effect on Marek's Disease Virus Pathogenesis and Tumorigenesis

The major histocompatibility complex (MHC) is crucial for appropriate immune responses against invading pathogens. Chickens possess a single predominantly-expressed class I molecule with strong associations between disease resistance and MHC haplotype. For Marek's disease virus (MDV) infections of chickens, the MHC haplotype is one of the major determinants of genetic resistance and susceptibility. VALO specific pathogen free (SPF) chickens are widely used in biomedical research and vaccine production. While valuable findings originate from MDV infections of VALO SPF chickens, their MHC haplotypes and associated disease resistance remained elusive. In this study, we used several typing systems to show that VALO SPF chickens possess MHC haplotypes that include B9, B9:02, B15, B19 and B21 at various frequencies. Moreover, we associate the MHC haplotypes to MDV-induced disease and lymphoma formation and found that B15 homozygotes had the lowest tumor incidence while B21 homozygotes had the lowest number of organs with tumors. Finally, we found transmission at variable levels to all contact birds except B15/B21 heterozygotes. These data have immediate implications for the use of VALO SPF chickens and eggs in the life sciences and add another piece to the puzzle of the chicken MHC complex and its role in infections with this oncogenic herpesvirus.

Characterization, Selection, and Trans-Species Polymorphism in the MHC Class II of Heermann’s Gull (Charadriiformes)

The major histocompatibility complex (MHC) enables vertebrates to cope with pathogens and maintain healthy populations, thus making it a unique set of loci for addressing ecology and evolutionary biology questions. The aim of our study was to examine the variability of Heermann’s Gull MHC class II (MHCIIB) and compare these loci with other Charadriiformes. Fifty-nine MHCIIB haplotypes were recovered from sixty-eight Heermann’s Gulls by cloning, of them, twelve were identified as putative true alleles, forty-five as unique alleles, and two as pseudogenes. Intra and interspecific relationships indicated at least two loci in Heermann’s Gull MHCIIB and trans-species polymorphism among Charadriiformes (coinciding with the documented evidence of two ancient avian MHCIIB lineages, except in the Charadriidae family). Additionally, sites under diversifying selection revealed a better match with peptide-binding sites inferred in birds than those described in humans. Despite the negative anthropogenic activity reported on Isla Rasa, Heermann’s Gull showed MHCIIB variability consistent with population expansion, possibly due to a sudden growth following conservation efforts. Duplication must play an essential role in shaping Charadriiformes MHCIIB variability, buffering selective pressures through balancing selection. These findings suggest that MHC copy number and protected islands can contribute to seabird conservation.

A guide to antigen processing and presentation

Antigen processing and presentation are the cornerstones of adaptive immunity. B cells cannot generate high-affinity antibodies without T cell help. CD4⁺ T cells, which provide such help, use antigen-specific receptors that recognize major histocompatibility complex (MHC) molecules in complex with peptide cargo. Similarly, eradication of virus-infected cells often depends on cytotoxic CD8⁺ T cells, which rely on the recognition of peptide-MHC complexes for their action. The two major classes of glycoproteins entrusted with antigen presentation are the MHC class I and class II molecules, which present antigenic peptides to CD8⁺ T cells and CD4⁺ T cells, respectively. This Review describes the essentials of antigen processing and presentation. These pathways are divided into six discrete steps that allow a comparison of the various means by which antigens destined for presentation are acquired and how the source proteins for these antigens are tagged for degradation, destroyed and ultimately displayed as peptides in complex with MHC molecules for T cell recognition.

Evolutionary pressures rendered by animal husbandry practices for avian influenza viruses to adapt to humans

Commercial poultry operations produce and crowd billions of birds every year, which is a source of inexpensive animal protein. Commercial poultry is intensely bred for desirable production traits, and currently presents very low variability at the major histocompatibility complex. This situation dampens the advantages conferred by the MHC’s high genetic variability, and crowding generates immunosuppressive stress. We address the proteins of influenza A viruses directly and indirectly involved in host specificities. We discuss how mutants with increased virulence and/or altered host specificity may arise if few class I alleles are the sole selective pressure on avian viruses circulating in immunocompromised poultry. This hypothesis is testable with peptidomics of MHC ligands. Breeding strategies for commercial poultry can easily and inexpensively include high variability of MHC as a trait of interest, to help save billions of dollars as a disease burden caused by influenza and decrease the risk of selecting highly virulent strains.

Differential immunological response detected in mRNA expression profiles among diverse chicken lines in response to Salmonella challenge

Salmonella enterica serovar Enteritidis is a bacterial pathogen that contributes to poultry production losses and human foodborne illness. The bacterium elicits a broad immune response involving both the innate and adaptive components of the immune system. Coordination of the immune response is largely directed by cytokines. The objective of the current study was to characterize the expression of a select set of cytokines and regulatory immune genes in three genetically diverse chicken lines after infection with S. Enteritidis. Leghorn, Fayoumi and broiler day-old chicks were orally infected with pathogenic S. Enteritidis or culture medium. At 2 and 18 h postinfection, spleens and ceca were collected and mRNA expression levels for 7 genes (GM-CSF, IL2, IL15, TGF-β1, SOCS3, P20K, and MHC class IIβ) were evaluated by real-time quantitative PCR. Genetic line had a significant effect on mRNA expression levels of IL15, TGF-β1, SOCS3 and P20K in the spleen and on P20K and MHC class IIβ in the cecum. Comparing challenged vs. unchallenged birds, the expression of SOCS3 and P20K mRNA were significantly higher in the spleen and cecum, while MHC class IIβ mRNA was significantly lower in spleen. Combining the current RNA expression results with those of previously reported studies on the same samples reveals distinct RNA expression profiles among the three genetic chicken lines and the 2 tissues. This study illustrates that these diverse genetic lines have distinctively different immune response to S. Enteritidis challenge within the spleen and the cecum.

Research Note: MHCY haplotype impacts Campylobacter jejuni colonization in a backcross [(Line 61 x Line N) x Line N] population

MHCY is a candidate region for influencing immune responses in chickens. MHCY contains multiple specialized, polymorphic MHC class I loci along with loci belonging to 4 additional gene families. In this study, MHCY haplotypes were tested for association with cecal colonization after Campylobacter jejuni infection of a backcross [(Line 6₁ × Line N) × Line N] population derived from 2 White Leghorn research lines, Line 6₁ and Line N, that were previously shown to exhibit heritable differences in colonization. Samples were obtained for 51 birds challenged with 10⁸ CFU Campylobacter jejuni at 3 wk of age. Viable C. jejuni in the ceca were enumerated 5 d postinfection and counts were log-transformed for analysis. Birds were assigned to either low or high colonization groups based on the individual count being below or above the mean bacterial count for all birds. The mean bacterial count of the low infection group differed significantly from the high infection group. Sex and MHCB haplotype had similar distributions within the 2 groups. Overall, 7 MHCY haplotypes were found to be segregating. Two were significantly associated with C. jejuni colonization. MHCY Y18 was associated with low colonization (P = 3.00 × 10⁻⁵); whereas MHCY Y11a was associated with high colonization (P = 0.008). The MHCY haplotype impacted the mean bacterial count among all birds with MHCY Y18 having the lowest bacterial count compared with MHCY Y11a and all other MHCY (Y5, Y7, Y8, Y11b, and Y11c) haplotypes. These findings support further investigation of the contribution of chicken MHCY in resistance to Campylobacter colonization.

Association of MHCY genotypes in lines of chickens divergently selected for high or low antibody response to sheep red blood cells

The chicken MHCY region contains members of several gene families including a family of highly polymorphic MHC class I genes that are structurally distinct from their classical class I gene counterparts. Genetic variability at MHCY could impart variability in immune responses, but robust tests for whether or not this occurs have been lacking. Here we defined the MHCY genotypes present in 2 sets of chicken lines selected for high or low antibody response, the Virginia Tech (VT) HAS and LAS, and the Wageningen University (WU) HA and LA lines. Both sets were developed under long-term bidirectional selection for differences in antibody responses following immunization with the experimental antigen sheep red blood cells. Lines in which selection was relaxed (VT HAR and LAR) or lacking (WU C) provided controls. We looked for evidence of association between MHCY genotypes and antibody titers. Chickens were typed for MHCY using a recently developed method based on a multilocus short tandem repeat sequence found across MHCY haplotypes. Five MHCY haplotypes were found segregating in the VT HAS and LAS lines. One haplotype was present only in HAS chickens, and another was present only in LAS chickens with distribution of the remaining 3 haplotypes differing significantly between the lines. In the WU HA and LA lines, there was a similar MHCY asymmetry. The control populations lacked similar asymmetries. These observations support the likelihood of MHCY genetics affecting heritable antibody responses and provide a basis for further investigations into the role of MHCY region genes in guiding immune responses in chickens.

Characterization of BoLA class II DQA and DQB by PCR-RFLP, cloning, and sequencing reveals sequence diversity in crossbred cattle

The BoLA class II DQA and DQB genes in crossbred cattle were studied using PCR-RFLP, cloning, and sequencing techniques. Seventy-two crossbred cattle (Vrindavani) were used in the current study. HaeIII and XbaI restriction enzymes digested DQA exon 2-3, revealing seven (HaeIII-A-G) and three (XbaI A-C) motifs, respectively. The BoLA-DQB gene was analyzed using PCR-RFLP with PstI and TaqI restriction enzymes, yielding five restriction motifs for each restriction enzyme (PstI-A-E and TaqI-A-E). In crossbred cattle, addition, deletion, and substitutions were observed in distinct sequences, resulting in variations in overall gene length. Changes in nucleotides at positions 64-80, 110-200, and 207-264 were largely responsible for polymorphism in DQA exon 2. The phylogenetic analysis predicted a high degree of nucleotide and amino acid changes in DQA exon 2-3 and DQB exon 2. DQA genes had a nucleotide dissimilarity of 0.3-25.4 percent, while DQB genes had a nucleotide dissimilarity of 1.5-14.3 percent. We cloned and sequenced 20 genotypes based on PCR-RFLP of the DQA and DQB genes. The current study observed variation in the DQA and DQB genes and will serve as a foundation for future research on the BoLA DQA and DQB genes.

Innate immune genes of the chicken MHC and related regions

Compared to the major histocompatibility complex (MHC) of typical mammals, the chicken BF/BL region is small and simple, with most of the genes playing central roles in the adaptive immune response. However, some genes of the chicken MHC are almost certainly involved in innate immunity, such as the complement component C4 and the lectin-like receptor/ligand gene pair BNK and Blec. The poorly expressed classical class I molecule BF1 is known to be recognised by natural killer (NK) cells and, analogous to mammalian immune responses, the classical class I molecules BF1 and BF2, the CD1 homologs and the butyrophilin homologs called BG may be recognised by adaptive immune lymphocytes with semi-invariant receptors in a so-called adaptate manner. Moreover, the TRIM and BG regions next to the chicken MHC, along with the genetically unlinked Y and olfactory/scavenger receptor regions on the same chromosome, have multigene families almost certainly involved in innate and adaptate responses. On this chicken microchromosome, the simplicity of the adaptive immune gene systems contrasts with the complexity of the gene systems potentially involved in innate immunity.

Comparison of major histocompatibility complex-B variability in Sri Lankan indigenous chickens with five global chicken populations using MHC-B SNP panel

In the present study, we investigated the major histocompatibility complex (MHC)-B haplotypes diversity of Sri Lankan indigenous chickens from three different geographical sites consisting of highly mixed populations using 90 SNPs in the MHC-B region. A total of 48 haplotypes were identified. Those included 37 novel haplotypes and 11 previously identified 'standard' haplotypes. The MHC-linked marker, LEI0258, had 23 alleles showing less diversity than defined by MHC-B SNP haplotypes. Among those identified haplotypes, five standard haplotypes-BSNP-O02, BSNP-M01, BSNP-A04, BSNP-K03, BSNP-T04-were most commonly observed, suggesting past introgression of imported breeds. Comparison of the MHC-B haplotypes of Sri Lankan and four other global populations with previously defined haplotypes indicated the sharing of 23 standard haplotypes with common origins. Novel haplotypes are population-specific and not shared among the geographical boundaries. Backyard indigenous chickens are unselected, highly crossbred, and generally thrive under dynamic environmental conditions. Hence free-range production systems may be responsible for maintaining high diversity in the MHC-B region with novel haplotypes.

A genome-wide scan to identify signatures of selection in two Iranian indigenous chicken ecotypes

Background

Various regions of the chicken genome have been under natural and artificial selection for thousands of years. The substantial diversity that exits among chickens from different geographic regions provides an excellent opportunity to investigate the genomic regions under selection which, in turn, will increase our knowledge about the mechanisms that underlie chicken diversity and adaptation. Several statistics have been developed to detect genomic regions that are under selection. In this study, we applied approaches based on differences in allele or haplotype frequencies (F_ST and hapFLK, respectively) between populations, differences in long stretches of consecutive homozygous sequences (ROH), and differences in allele frequencies within populations (composite likelihood ratio (CLR)) to identify inter- and intra-populations traces of selection in two Iranian indigenous chicken ecotypes, the Lari fighting chicken and the Khazak or creeper (short-leg) chicken.

Results

Using whole-genome resequencing data of 32 individuals from the two chicken ecotypes, approximately 11.9 million single nucleotide polymorphisms (SNPs) were detected and used in genomic analyses after quality processing. Examination of the distribution of ROH in the two populations indicated short to long ROH, ranging from 0.3 to 5.4 Mb. We found 90 genes that were detected by at least two of the four applied methods. Gene annotation of the detected putative regions under selection revealed candidate genes associated with growth (DCN, MEOX2 and CACNB1), reproduction (ESR1 and CALCR), disease resistance (S1PR1, ALPK1 and MHC-B), behavior pattern (AGMO, GNAO1 and PSEN1), and morphological traits (IHH and NHEJ1).

Conclusions

Our findings show that these two phenotypically different indigenous chicken populations have been under selection for reproduction, immune, behavioral, and morphology traits. The results illustrate that selection can play an important role in shaping signatures of differentiation across the genomic landscape of two chicken populations.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12711-021-00664-9.

Pathogenesis and shedding of Usutu virus in juvenile chickens

Usutu virus (USUV; family: Flaviviridae, genus: Flavivirus), is an emerging zoonotic arbovirus that causes severe neuroinvasive disease in humans and has been implicated in the loss of breeding bird populations in Europe. USUV is maintained in an enzootic cycle between ornithophilic mosquitos and wild birds. As a member of the Japanese encephalitis serocomplex, USUV is closely related to West Nile virus (WNV) and St. Louis encephalitis virus (SLEV), both neuroinvasive arboviruses endemic in wild bird populations in the United States. An avian model for USUV is essential to understanding zoonotic transmission. Here we describe the first avian models of USUV infection with the development of viremia. Juvenile commercial ISA Brown chickens were susceptible to infection by multiple USUV strains with evidence of cardiac lesions. Juvenile chickens from two chicken lines selected for high (HAS) or low (LAS) antibody production against sheep red blood cells showed markedly different responses to USUV infection. Morbidity and mortality were observed in the LAS chickens, but not HAS chickens. LAS chickens had significantly higher viral titers in blood and other tissues, as well as oral secretions, and significantly lower development of neutralizing antibody responses compared to HAS chickens. Mathematical modelling of virus-host interactions showed that the viral clearance rate is a stronger mitigating factor for USUV viremia than neutralizing antibody response in this avian model. These chicken models provide a tool for further understanding USUV pathogenesis in birds and evaluating transmission dynamics between avian hosts and mosquito vectors.

Genetic Diversity of MHC B-F/B-L Region in 21 Chicken Populations

The chicken major histocompatibility complex (MHC) on chromosome 16 is the most polymorphic region across the whole genome, and also an ideal model for genetic diversity investigation. The MHC B-F/B-L region is 92 kb in length with high GC content consisting of 18 genes and one pseudogene (Blec4), which plays important roles in immune response. To evaluate polymorphism of the Chinese indigenous chickens as well as to analyze the effect of selection to genetic diversity, we used WaferGen platform to identify sequence variants of the B-F/B-L region in 21 chicken populations, including the Red Jungle Fowl (RJF), Cornish (CS), White Leghorns (WLs), 16 Chinese domestic breeds, and two well-known inbred lines 63 and 72. A total of 3,319 single nucleotide polymorphism (SNPs) and 181 INDELs in the B-F/B-L region were identified among 21 populations, of which 2,057 SNPs (62%) and 159 INDELs (88%) were novel. Most of the variants were within the intron and the flanking regions. The average variation density was 36 SNPs and 2 INDELs per kb, indicating dramatical high diversity of this region. Furthermore, BF2 was identified as the hypervariable genes with 67 SNPs per kb. Chinese domestic populations showed higher diversity than the WLs and CS. The indigenous breeds, Nandan Yao (NY), Xishuangbanna Game (XG), Gushi (GS), and Xiayan (XY) chickens, were the top four with the highest density of SNPs and INDELs. The highly inbred lines 63 and 72 have the lowest diversity, which might be resulted from a long-term intense selection for decades. Collectively, we refined the genetic map of chicken MHC B-F/B-L region, and illustrated genetic diversity of 21 chicken populations. Abundant genetic variants were identified, which not only strikingly expanded the current Ensembl SNP database, but also provided comprehensive data for researchers to further investigate association between variants in MHC and immune traits.

Exonic SNP in MHC-DMB2 is associated with gene expression and humoral immunity in Japanese quails

The DMB2 gene is widely expressed at high levels in avian. This gene plays an important role in humoral immunity. The aim of this study was to investigate the effects of 361 G > C Single nucleotide polymorphism (SNP) on DMB2 protein structure and gene expression to determine how the 361 G > C SNP affects humoral immune response in Japanese quails. 0.2 mL of 5% sheep red blood cell (SRBC) was injected into breast muscle of 130 Japanese quails on 28 days. After DNA extraction, PCR was carried out to amplify a 333-base pair DNA fragment from the exon 2 of DMB2 gene. The pattern of all samples was determined through RFLP technique. PCR-RFLP results identified two alleles segregating (C, G) as three genotypes (CC, CG and GG) in Japanese Quails. The antibody response to SRBC with CC genotype was significantly higher than the CG and GG genotypes (P < 0.01). In silico analysis showed that the 361 G > C SNP has no effect on the physicochemical properties and 3D structure. The results of RT-qPCR indicated that the effect of genotype on gene expression is significant, so that the expression of CC genotype is more than CG and GG genotype. It can be inferred that the 361 G > C SNP in the exon 2 of MHC-DMB2 gene is not desirable. This mutation decreases humoral immune response by reducing DMB2 gene expression.

The Marek's Disease Virus Unique Gene MDV082 Is Dispensable for Virus Replication but Contributes to a Rapid Disease Onset

Marek's disease virus (MDV) is a highly oncogenic alphaherpesvirus of chickens that causes lymphomas in various organs. Most MDV genes are conserved among herpesviruses, while others are unique to MDV and may contribute to pathogenesis and/or tumor formation. High transcript levels of the MDV-specific genes MDV082, RLORF11, and SORF6 were recently detected in lytically infected cells; however, it remained elusive if the respective proteins are expressed and if they play a role in MDV pathogenesis. In this study, we first addressed if these proteins are expressed by inserting FLAG tags at their N or C termini. We could demonstrate that among the three genes tested, MDV082 is the only gene that encodes a protein and is expressed very late in MDV plaques in vitro. To investigate the role of this novel MDV082 protein in MDV pathogenesis, we generated a recombinant virus that lacks expression of the MDV082 protein. Our data revealed that the MDV082 protein contributes to the rapid onset of Marek's disease but is not essential for virus replication, spread, and tumor formation. Taken together, this study sheds light on the expression of MDV-specific genes and unravels the role of the late protein MDV082 in MDV pathogenesis. IMPORTANCE MDV is a highly oncogenic alphaherpesvirus that causes Marek's disease in chickens. The virus causes immense economic losses in the poultry industry due to the high morbidity and mortality, but also the cost of the vaccination. MDV encodes over 100 genes that are involved in various processes of the viral life cycle. Functional characterization of MDV genes is an essential step toward understanding the complex virus life cycle and MDV pathogenesis. Here, we have identified a novel protein encoded by MDV082 and two potential noncoding RNAs (RLORF11 and SORF6). The novel MDV082 protein is not needed for efficient MDV replication and tumor formation. However, our data demonstrate that the MDV082 protein is involved in the rapid onset of Marek's disease.

MHC-B variation in maternal and paternal synthetic lines of the Argentinian Campero INTA chicken

The Campero-INTA chicken of Argentina was developed to provide a robust bird that can survive under Argentinian pasture conditions with no significant additional nutrition, producing a source of animal protein for small producers or low-income families. In previous work, we described the AH paternal line of Campero and its Major Histocompatibility Complex B region (MHC-B) variation. In this work we analyzed the three remaining synthetic lines used to produce the Campero-INTA production bird: lines AS, A, and E. Because of the association between variation within the MHC of chickens and disease resistance, MHC variation within this breed is of particular interest. MHC variability within the lines used to produce the Campero-INTA chicken was examined using a 90 SNP panel encompassing the chicken MHC-B region plus the VNTR, LEI0258, located within the chicken MHC. Across all 4lines 12 haplotypes were found, with 7 of these being previously reported in North America/European breeds, reflecting the original breed sources for these birds. Three Campero unique haplotypes were found, 2 of which likely originated from MHC recombination events. MHC-B variation for all lines involved with production of the final Campero-INTA bird has now been determined.