Mannan-binding lectin (MBL) in two chicken breeds and the correlation with experimental Pasteurella multocida infection

Analysis of Mannose-Binding Lectin Protein and mRNA Levels on Selected Chicken Breeds in South Africa

BACKGROUND

Mannose-binding lectin (MBL) is a key component of the innate immune system that plays a crucial role in binding to the microbial sugar surface to recognize and eliminate pathogens by activating the complement system.

OBJECTIVE

To detect and quantify the MBL protein concentration and chicken MBL expression in selected chicken breeds in South Africa.

METHODS

Forty-five blood samples from three indigenous chicken breeds, Ovambo (OV = 9), Venda (VD = 9) and Potchefstroom Koekoek (PK = 9), and two exotic chicken breeds, Rhode Island Red (RIR = 9) and Lohmann Brown (LB = 9), were used for MBL protein concentration using enzyme-linked immunosorbent assay (ELISA) techniques. Also 20 liver samples from symptomatic two indigenous chicken breeds, OV (5) and PK (5), and two exotic chicken breeds, RIR (5) and LB (5), were used for MBL expression using quantitative polymerase chain reaction (qPCR) techniques. A general linear model was done using Tukey's multiple comparison post hoc test.

RESULTS

The findings revealed MBL protein concentration from 5.26 to 18.56 µg/mL. The LB breed had the lowest mean 6.40 ± 0.80 µg/mL, whereas the PK breed had the highest mean MBL concentration of 17.70 ± 0.24 µg/mL of MBL protein concentration. At 12, 25 and 35 weeks, the MBL proteins of OV, VD, PK, RIR and LB varied significantly at p ≤ 0.05. The mRNA MBL expression of OV and LB breeds showed a 1-fold decrease in MBL expression, while RIR showed a 2-fold increase in MBL expression, and the PK showed more than a 3-fold increase in MBL expression relative to the control. The least-squares means for OV, LB, PK and RIR mRNA MBL expression were 0.54 ± 0.19, 0.68 ± 0.30, 4.46 ± 2.76 and 2.89 ± 0.19 µg/mL, respectively.

CONCLUSION

MBL protein was detected and quantified with distinct differences in concentration and expression levels  at the presence of mycoplasma gallisepticum among the sampled South African chicken breeds. This highlights the genetic diversity of MBL as a tool for disease prevention in South African chicken breeds.

Immunogenicity and protection of a Pasteurella multocida strain with a truncated lipopolysaccharide outer core in ducks

Pasteurella multocida infection frequently causes fowl cholera outbreaks, leading to huge economic losses to the poultry industry worldwide. This study developed a novel live attenuated P. multocida vaccine strain for ducks named PMZ2 with deletion of the gatA gene and first four bases of the hptE gene, both of which are required for the synthesis of the lipopolysaccharide (LPS) outer core. PMZ2 produced a truncated LPS phenotype and was highly attenuated in ducks with a > 10⁵-fold higher LD₅₀ than the wild-type strain. PMZ2 colonized the blood and organs, including the spleen, liver and lung, at remarkably reduced levels, and its high dose of oral infection did not cause adverse effects on body temperatures and body weights in ducks. To evaluate the vaccine efficacy of the mutant, ducklings were inoculated orally or intranasally with PMZ2 or PBS twice and subsequently subjected to a lethal challenge. Compared with the PBS control, PMZ2 immunization stimulated significantly elevated serum IgG, bile IgA and tracheal IgA responses, especially after the boost immunization in both the oral and intranasal groups, and the induced serum had significant bactericidal effects against the wild-type strain. Furthermore, the two PMZ2 immunization groups exhibited alleviated tissue lesions and significantly decreased bacterial loads in the blood and organs compared with the PBS group post-challenge. All the ducks in the PMZ2 oral and intranasal groups survived the challenge, while 70% of ducks in the PBS group succumbed to the challenge. Thus, the P. multocida mutant with mutation of the gatA gene and part of the hptE gene proved to be an effective live attenuated vaccine candidate for prevention of fowl cholera in ducks.

Erysipelothrix rhusiopathiae-specific T-cell responses after experimental infection of chickens selectively bred for high and low serum levels of mannose-binding lectin

Erysipelas, caused by infection with Erysipelothrix rhusiopathiae (ER) is an important emerging disease in laying hens. We have earlier observed prominent mannose-binding lectin (MBL) acute phase responses in experimentally ER infected chickens. The present study aimed to further examine immune responses to ER by using chickens selectively bred for high (L10H) and low (L10L) serum MBL levels. Chickens were infected with ER at 3 weeks of age and immune parameters and bacterial load were monitored in blood until day 18 after infection. Blood and spleen leukocytes collected on day 18 were stimulated in vitro with ER antigens and blast transformation of different T-cell populations was assessed. The ER infection gave a very varied outcome and no clear differences were observed between L10H and L10L chickens with respect to leukocyte counts, bacterial load or clinical outcome. Nonetheless, rapid innate responses, e.g., heterophilia and increased serum MBL levels were noted in bacteraemic chickens. All ER infected chickens also showed transient increased expression of mannose receptor MRC1L-B and decreased expression of major histocompatibility complex II on monocytes day 1 after infection indicating monocyte activation or relocation. In vitro ER stimulation showed antigen specific blast transformation of CD4+, TCRγ/δ-CD8αβ+ and TCRγ/δ+CD8αβ+ spleen cells from all infected chickens. For CD4+ and TCRγ/δ-CD8αβ+ cells the proportions of blast transformed cells were significantly higher for samples from L10L chickens than those for samples from L10H chickens. This is the first observation of ER-specific T-cells in chickens and interestingly a Th1-type response comprising cytotoxic T-cells was indicated.

Activity of Mannose-Binding Lectin on Bacterial-Infected Chickens-A Review

Simple Summary

In the quest to combat bacterial-related diseases in chickens, different methods, of which some are less economical and less effective on the long-term, have been adapted. However, chickens possess mannose-binding lectin (MBL) which could be vital in managing pathogenic bacteria in chickens. MBL is one of the soluble proteins secreted by the chicken’s innate immune system which can be activated when chickens are exposed to chicken-related diseases. This review explains how mannose-binding lectin activation can help in fighting bacterial pathogens in chickens. This knowledge is believed to reduce incessant use of antibiotics and to assist in developing a profitable breeding program with less or no adverse effect on the chicken, human and the environment.

Abstract

In recent years, diseases caused by pathogenic bacteria have profoundly impacted chicken production by causing economic loss in chicken products and by-product revenues. MBL (mannose-binding lectin) is part of the innate immune system (IIS), which is the host’s first line defense against pathogens. The IIS functions centrally by identifying pathogen-specific microorganism-associated molecular patterns (MAMPs) with the help of pattern recognition receptors (PRRs). Studies have classified mannose-binding lectin (MBL) as one of the PRR molecules which belong to the C-type lectin family. The protective role of MBL lies in its ability to activate the complement system via the lectin pathway and there seems to be a direct link between the chicken’s health status and the MBL concentration in the serum. Several methods have been used to detect the presence, the level and the structure of MBL in chickens such as Enzyme-linked immunosorbent assay (ELISA), Polymerase Chain Reaction (PCR) among others. The concentration of MBL in the chicken ranges from 0.4 to 35 µg/mL and can be at peak levels at three to nine days at entry of pathogens. The variations observed are known to depend on the bacterial strains, breed and age of the chicken and possibly the feed manipulation strategies. However, when chicken MBL (cMBL) becomes deficient, it can result in malfunctioning of the innate immune system, which can predispose chickens to diseases. This article aimed to discuss the importance and components of mannose-binding lectin (MBL) in chickens, its mode of actions, and the different methods used to detect MBL. Therefore, more studies are recommended to explore the causes for low and high cMBL production in chicken breeds and the possible effect of feed manipulation strategies in enhancing cMBL production.

Kinetics of activation marker expression after in vitro polyclonal stimulation of chicken peripheral T cells

A comprehensive analysis of T cell activation markers in chicken is lacking. Kinetics of T cell activation markers (CD25, CD28, CD5, MHC-II, CD44, and CD45) in response to in vitro stimulation of peripheral blood mononuclear cells with concanavalin A (Con A) were evaluated between two chicken lines selected for high and low levels of mannose-binding lectin in serum (L10H and L10L, respectively) by flow cytometry. L10H chickens showed a stronger response to Con A based on the frequency of T cell blasts in both the CD4⁺ and CD8⁺ compartment. The majority of the proliferating CD4⁺ and CD8⁺ T cells expressed CD25. Proliferating T cells were seen both in the CD4⁺  MHC-II^+/- and CD8⁺  MHC-II^+/- population. For both CD4⁺ and CD8⁺ T cells, frequencies of CD25⁺ and MHC-II⁺ T cells were increased 24 h after stimulation. CD28⁺ frequencies were only increased on CD8⁺ T cells 48 h after stimulation. An increase in the relative surface expression based on mean fluorescence intensity (MFI) upon activation was observed for most markers except CD5. For CD4⁺ T cells, CD28 expression increased 24 h after stimulation whereas MHC-II expression increased after 48 h. For CD8⁺ T cells, a tendency toward an increase in CD25 expression was observed. CD28 expression started to increase 24 h after stimulation and only a transient peak in MHC-II expression on CD8⁺ T cells was observed after 24 h. CD44 and CD45 expressed on CD4⁺ and CD8⁺ T cells increased 24-72 h after stimulation. In summary, the frequency of CD25⁺ and MHC-II⁺ T cells were shown to be early markers (24 h) for in vitro activation of both CD4⁺ and CD8⁺ T cells. Frequency of CD28⁺ T cells was a later marker (48 h) and only for CD8⁺ T cells. Surface expression of all markers (MFI) increased permanently or transiently upon activation except for CD5.

Immune responses upon experimental Erysipelothrix rhusiopathiae infection of naïve and vaccinated chickens

Erysipelas, a disease caused by Erysipelothrix rhusiopathiae (ER), is an increasing problem in laying hens housed in cage-free systems. This study aimed to monitor immune responses during ER infection of naïve chickens and chickens vaccinated intra muscularly with a commercial inactivated ER vaccine. Chickens were infected intra muscularly with ER at 30 days of age and blood leukocyte counts, serum levels of mannose binding lectin (MBL) and ER-specific IgY were monitored until the experiment was terminated at day 15 after infection. ER was detected in blood from more chickens and at higher bacterial counts in the naïve group (day 1: 1 of 7 chickens; day 3: 6 of 6 chickens) than in the vaccinated group (day 1: 0 of 7 chickens; day 3: 1 of 6 chickens). During the acute phase of infection transient increases in circulating heterophil numbers and serum MBL levels were detected in all ER infected chickens but these responses were prolonged in chickens from the naïve group compared to vaccinated chickens. Before infection IgY titers to ER in vaccinated chickens did not differ significantly from those of naïve chickens but vaccinated chickens showed significantly increased IgY titers to ER earlier after infection compared to chickens in the naïve group. In conclusion, the ER infection elicited prompt acute innate responses in all chickens. Vaccinated chickens did not have high IgY titers to ER prior to infection but did however show lower levels of bacteraemia and their acute immune responses were of shorter duration.

Avian coronavirus infection induces mannose-binding lectin production in dendritic cell precursors of chicken lymphoid organs

The aim of this immunocytochemical study was to compare mannose-binding lectin (MBL) production induced by avian coronavirus in the spleen and caecal tonsil (CT). One-day-old specific-pathogen-free (SPF) chickens were experimentally infected with six QX field isolates and the H120 vaccine strain. In the negative control birds, the spleen was MBL negative, while the CT showed scattered MBL-positive cells in close proximity and within the surface epithelium and germinal centre (GC)-like cell clusters. MBL was detectable in the ellipsoid-associated cells (EACs) and cell clusters in the periarterial lymphoid sheath (PALS) by 7 days post infection (dpi). In both organs, the MBL-positive cells occupy antigen-exposed areas, indicating that GC formation depends on resident precursors of dendritic cells. The majority of MBL-positive EACs express the CD83 antigen, providing evidence that coronavirus infection facilitated the maturation of dendritic cell precursors. Surprisingly, co-localisation of MBL and CD83 was not detectable in the CT. In the spleen (associated with circulation), the EACs producing MBL and expressing CD83 are a common precursor of both follicular (FDC) and interdigitating dendritic cells (IDC). In the CT (gut-associated lymphoid tissue, GALT) the precursors of FDC and IDC are MBL-producing cells and CD83-positive cells, respectively. In the CT the two separate precursors of lymphoid dendritic cells provide some 'autonomy' for the GALT.

Dose-dependent differential resistance of inbred chicken lines to avian pathogenic Escherichia coli challenge

Avian pathogenic E. coli (APEC) cause severe respiratory and systemic disease. To address the genetic and immunological basis of resistance, inbred chicken lines were used to establish a model of differential resistance to APEC, using strain O1 of serotype O1:K1:H7. Inbred lines 7₂, 15I and C.B12 and the outbred line Novogen Brown were inoculated via the airsac with a high dose (10⁷ colony-forming units, CFU) or low dose (10⁵ CFU) of APEC O1. Clinical signs, colibacillosis lesion score and bacterial colonization of tissues after high dose challenge were significantly higher in line 15I and C.B12 birds. The majority of the 15I and C.B12 birds succumbed to the infection by 14 h post-infection, whilst none of the line 7₂ and the Novogen Brown birds developed clinical signs. No difference was observed after low dose challenge. In a repeat study, inbred lines 7₂ and 15I were inoculated with low, intermediate or high doses of APEC O1 ranging from 10⁵ to 10⁷ CFU. The colonization of lung was highest in line 15I after high dose challenge and birds developed clinical signs; however, colonization of blood and spleen, clinical signs and lesion score were not different between lines. No difference was observed after intermediate or low dose challenge. Ex vivo, the phagocytic and bactericidal activity of lung leukocytes from line 7₂ and 15I birds did not differ. Our data suggest that although differential resistance of inbred lines 7₂, 15I and C.B12 to APEC O1 challenge is apparent, it is dependent on the infectious dose. Research Highlights Lines 15I and C.B12 are more susceptible than line 7₂ to a high dose of APEC O1. Differential resistance is dose-dependent in lines 15I and 7₂. Phagocytic and bactericidal activity is similar and dose independent.

Comparison of growth performance and immune parameters of three commercial chicken lines used in organic production

Owing to the higher demands for avoiding medication and antibiotics, health status of the production animals plays an important role in the poultry industry, especially in organic poultry systems. Immunity plays a major role in keeping the host free from disease, and it is evident that the host's genetic make-up influences immunity and disease resistance/susceptibility in chickens. Previously, breeding strategies aimed at selection for resistance against specific diseases with the risk of creating less disease resistance against other pathogens. Changing breeding strategies towards selection of chickens with a more general and broad disease resistance or robustness may therefore improve the overall health status, animal welfare, and food security in the poultry production. The aim of this study was therefore to compare the immunocompetence of the presumed "robust" Hellevad chickens with two chicken lines widely used in organic production, Bovans Brown (Bovans) and Hisex White (Hisex). The chickens were subjected to a routine vaccination program comprising one parasite and four viral vaccines. The current study indicates that considerable differences in immunocompetence may exist between commercial layer lines used in organic production. The Hellevad chickens were found to have higher body weight at the end of the experiment (17 weeks of age) than the other two lines. Furthermore, Hellevad and Hisex chickens were found to have higher levels of humoral innate immunity with regard to sample to positive ratio of natural antibodies in serum and concentration of mannose-binding lectin in serum as compared to Bovans. Moreover, indications of an inflammatory response were observed in the Bovans at week 5, corresponding to 1 week after vaccination with live infectious bursal disease virus. With regard to adaptive immune parameters such as IgY concentration in blood and infectious bursal disease virus (IBDV)-specific antibody titres, the Hellevad and Hisex chickens had lower levels than the Bovans. How the differences observed in growth and immune parameters in the three chicken lines influence the immune protection against infection needs to be studied further.

Broilers with low serum Mannose-binding Lectin show increased fecal shedding of Salmonella enterica serovar Montevideo

Mannose-binding lectin (MBL) is a key molecule in innate immunity. MBL binds to carbohydrates on the surface of pathogens, initiating the complement system via the lectin-dependent pathway or facilitates opsonophagocytosis. In vivo studies using inbred chicken lines differing in MBL serum concentration indicate that chicken MBL affects Salmonella resistance; further studies are imperative in conventional broiler chickens. In this study 104 conventional day-old chickens (offspring from a cross between Cobb 500 male and female parent breeders) were orally infected with Salmonella enterica subsp. enterica serovar Montevideo. The chickens were divided into two groups based on polymorphisms in their MBL promoter region, designated L/L for low serum concentrations of MBL and L/H for medium serum concentrations of MBL. A semi-quantitative real-time PCR method for detection of Salmonella in cloacal swabs was used, the log10 CFU quantification was based on a standard curve from artificially spiked cloacal swab samples pre-incubated for 8 h with known concentrations of Salmonella ranging from 10(1) to 10(6) CFU/swabs, with an obtained amplification efficiency of 102% and a linear relationship between the log10 CFU and the threshold cycle Ct values of (R(2) = 0.99). The L/L chickens had significantly higher Log10 CFU/swab at week 5 post infection (pi) than the L/H chickens. A repetition of the study with 86 L/L and 18 L/H chickens, also gave significantly higher log10 CFU ± SEM in cloacal swabs, using the semi-quantitative real-time PCR method from L/L chickens than from the L/H chickens at week 5 pi. These results indicate that genetically determined basic levels of MBL may influence S. Montevideo susceptibility.

RNA sequencing-based analysis of the spleen transcriptome following infectious bronchitis virus infection of chickens selected for different mannose-binding lectin serum concentrations

BACKGROUND

Avian infectious bronchitis is a highly contagious disease of the upper-respiratory tract caused by infectious bronchitis virus (IBV). Understanding the molecular mechanisms involved in the interaction between innate and adaptive immune responses to IBV infection is a crucial element for further improvements in strategies to control IB. To this end, two chicken lines, selected for high (L10H line) and low (L10L line) serum concentration of mannose-binding lectin (MBL) were studied. In total, 32 birds from each line were used. Sixteen birds from each line were infected with IBV and sixteen were left uninfected. Eight uninfected and infected birds from each line were euthanized at 1 and 3 weeks post infection. RNA sequencing was performed on spleen samples from all 64 birds and differential gene expression analysis was performed for four comparisons: L10L line versus L10H line for uninfected birds at weeks 1 and 3, respectively, and in the same way for infected birds. Functional analysis was performed using Gene Ontology (GO) Immune System Process terms specific for Gallus gallus.

RESULTS

Comparing uninfected L10H and L10L birds, we identified 1698 and 1424 differentially expressed (DE) genes at weeks 1 and 3, respectively. For the IBV-infected birds, 1934 and 866 DE genes were identified between the two lines at weeks 1 and 3, respectively. The two most enriched GO terms emerging from the comparison of uninfected birds between the two lines were "Lymphocyte activation involved in immune response" and "Somatic recombination of immunoglobulin genes involved in immune response" at weeks 1 and 3, respectively. When comparing IBV-infected birds between the two lines, the most enriched GO terms were "Alpha-beta T cell activation" and "Positive regulation of leukocyte activation" at weeks 1 and 3, respectively.

CONCLUSIONS

Healthy birds from the two lines showed significant differences in expression profiles for subsets of adaptive and innate immunity-related genes, whereas comparison of the IBV-infected birds from the two lines showed differences in expression of immunity-related genes involved in T cell activation and proliferation. The observed transcriptome differences between the two lines indicate that selection for MBL had influenced innate as well as adaptive immunity.

Immunogenetic heterogeneity in a widespread ungulate: the European roe deer (Capreolus capreolus)

Understanding how immune genetic variation is shaped by selective and neutral processes in wild populations is of prime importance in both evolutionary biology and epidemiology. The European roe deer (Capreolus capreolus) has considerably expanded its distribution range these last decades, notably by colonizing agricultural landscapes. This range shift is likely to have led to bottlenecks and increased roe deer exposure to a new range of pathogens that until recently predominantly infected humans and domestic fauna. We therefore investigated the historical and contemporary forces that have shaped variability in a panel of genes involved in innate and acquired immunity in roe deer, including Mhc-Drb and genes encoding cytokines or toll-like receptors (TLRs). Together, our results suggest that genetic drift is the main contemporary evolutionary force shaping immunogenetic variation within populations. However, in contrast to the classical view, we found that some innate immune genes involved in micropathogen recognition (e.g. Tlrs) continue to evolve dynamically in roe deer in response to pathogen-mediated positive selection. Most studied Tlrs (Tlr2, Tlr4 and Tlr5) had similarly high levels of amino acid diversity in the three studied populations including one recently established in southwestern France that showed a clear signature of genetic bottleneck. Tlr2 implicated in the recognition of Gram-positive bacteria in domestic ungulates, showed strong evidence of balancing selection. The high immunogenetic variation revealed here implies that roe deer are able to cope with a wide spectrum of pathogens and to respond rapidly to emerging infectious diseases.

Immune gene expression in the spleen of chickens experimentally infected with Ascaridia galli

Ascaridia galli is a gastrointestinal nematode infecting chickens. Chickens kept in alternative rearing systems or at free-range experience increased risk for infection with resulting high prevalences. A. galli infection causes reduced weight gain, decreased egg production and in severe cases increased mortality. More importantly, the parasitised chickens are more susceptible to secondary infections and their ability to develop vaccine-induced protective immunity against other diseases may be compromised. Detailed information about the immune response to the natural infection may be exploited to enable future vaccine development. In the present study, expression of immune genes in the chicken spleen during an experimental infection with A. galli was investigated using the Fluidigm(®) BioMark™ microfluidic qPCR platform which combines automatic high-throughput with attractive low sample and reagent consumption. Spleenic transcription of immunological genes was compared between infected chickens and non-infected controls at week 2, 6, and 9 p.i. corresponding to different stages of parasite development/maturation. At week 2 p.i. increased expression of IL-13 was observed in infected chickens. Increased expression of MBL, CRP, IFN-α, IL-1β, IL-8, IL-12β and IL-18 followed at week 6 p.i. and at both week 6 and 9 p.i. expression of DEFβ1 was highly increased in infected chickens. In summary, apart from also earlier reported increased expression of the Th2 signature cytokine IL-13 we observed only few differentially expressed genes at week 2 p.i. which corresponds to the larvae histotrophic phase. In contrast, we observed increased expression of pro-inflammatory cytokines and acute phase proteins in infected chickens, by week 6 p.i. where the larvae re-enter the intestinal lumen. Increased expression of DEFβ1 was observed in infected chickens at week 6 p.i. but also at week 9 p.i. which corresponds to a matured stage where adult worms are present in the intestinal lumen.

Chicken mannose-binding lectin function in relation to antibacterial activity towards Salmonella enterica

Mannose-binding lectin (MBL) is a C-type serum lectin of importance in innate immunity. Low serum concentrations of MBL have been associated with greater susceptibility to infections. In this study, binding of purified chicken MBL (cMBL) to Salmonella enterica subsp. enterica (S. enterica) serotypes B, C1 and D was investigated by flow cytometry, and Staphylococcus aureus (S. aureus) was used for comparison. For S. enterica the C1 serotypes were the only group to exhibit binding to cMBL. Furthermore, functional studies of the role of cMBL in phagocytosis and complement activation were performed. Spiking with cMBL had a dose-dependent effect on the HD11 phagocytic activity of S. enterica subsp. enterica serovar Montevideo, and a more pronounced effect in a carbohydrate competitive assay. This cMBL dose dependency of opsonophagocytic activity by HD11 cells was not observed for S. aureus. No difference in complement-dependent bactericidal activity in serum with high or low cMBL concentrations was found for S. Montevideo. On the other hand, serum with high concentrations of cMBL exhibited a greater bactericidal activity to S. aureus than serum with low concentrations of cMBL. The results presented here emphasise that chicken cMBL exhibits functional similarities with its mammalian counterparts, i.e. playing a role in opsonophagocytosis and complement activation.

Characterization of cellular and humoral immune responses after IBV infection in chicken lines differing in MBL serum concentration

Chickens from two inbred lines selected for high (L10H) or low (L10L) mannose-binding lectin (MBL) serum concentrations were infected with infectious bronchitis virus (IBV), and innate as well as adaptive immunological parameters were measured throughout the experimental period. Chickens with high MBL serum concentrations were found to have less viral load in the trachea than chickens with low MBL serum concentrations indicating that these chickens were less severely affected by the infection. This study is the first to show that MBL expression is present in the lungs of healthy chickens and that the expression is upregulated at days 3 postinfection (p.i.) in L10H chickens. Furthermore, in the liver of infected chickens, the MBL expression was upregulated at day 7 p.i., despite the fact that the MBL serum concentrations were decreased below baseline at that time point. The number of TCRγδ+CD8α+ cells in the blood of noninfected chickens increased from week 0 to 3 p.i. However, the number of cells was higher in L10H chickens than in L10L chickens throughout the experiment. No increase was observed in the number of TCRγδ+CD8α+ cells in the blood of the infected L10H and L10L chickens. The numbers of B cells at week 3 p.i. were higher for noninfected L10L chickens than for the other chickens. No differences were observed between the infected and noninfected L10H chickens or between the infected L10H and L10L chickens. Furthermore, at week 3 p.i., the number of monocytes was higher in infected and noninfected L10H chickens than in the infected and noninfected L10L chickens. Thus, these results indicate that MBL is produced locally and may be involved in the regulation of the cellular immune response after an IBV infection. However, MBL did not appear to influence the humoral immune response after IBV infection in this study.

The consequence of low mannose-binding lectin plasma concentration in relation to susceptibility to Salmonella Infantis in chickens

Mannose-binding lectin (MBL) is a key protein in innate immunity. MBL binds to carbohydrates on the surface of pathogens, where it initiates complement activation via the lectin-dependent pathway or facilitates opsonophagocytosis. In vitro studies have shown that human MBL is able to bind to Salmonella, but knowledge in relation to chicken MBL and Salmonella is lacking. In order to study this relation day-old chickens from two selected lines L10H and L10L, differing in MBL serum concentration, were either orally infected with S. Infantis (S.123443) or kept as non-infected controls. The differences between healthy L10H and L10L chicken sublines were more profound than differences caused by the S. Infantis infection. The average daily body weight was higher for L10H than for L10L, regardless of infection, indicating beneficial effects of MBL selection on growth. Salmonella was detected in cloacal swabs and the number of Salmonella positive chickens during the experiment was significantly higher in L10L than L10H, indicating that MBL may affect the magnitude of Salmonella colonisation in day-old chickens. MBL expression was determined in ceca tissue by real-time RT-PCR. L10H chickens showed a significantly higher relative expression than L10L at days 1 and 41 pi, regardless of infection. Finally, flow cytometric analysis of whole blood from infected chickens showed that L10H had a significantly higher count of all assessed leucocyte subsets on day 5 pi, and also a higher count of monocytes on day 12 pi than L10L. No difference was observed between infected and non-infected L10L chicken.

Genome-wide patterns of genetic variation in two domestic chickens

Domestic chickens are excellent models for investigating the genetic basis of phenotypic diversity, as numerous phenotypic changes in physiology, morphology, and behavior in chickens have been artificially selected. Genomic study is required to study genome-wide patterns of DNA variation for dissecting the genetic basis of phenotypic traits. We sequenced the genomes of the Silkie and the Taiwanese native chicken L2 at ∼23- and 25-fold average coverage depth, respectively, using Illumina sequencing. The reads were mapped onto the chicken reference genome (including 5.1% Ns) to 92.32% genome coverage for the two breeds. Using a stringent filter, we identified ∼7.6 million single-nucleotide polymorphisms (SNPs) and 8,839 copy number variations (CNVs) in the mapped regions; 42% of the SNPs have not found in other chickens before. Among the 68,906 SNPs annotated in the chicken sequence assembly, 27,852 were nonsynonymous SNPs located in 13,537 genes. We also identified hundreds of shared and divergent structural and copy number variants in intronic and intergenic regions and in coding regions in the two breeds. Functional enrichments of identified genetic variants were discussed. Radical nsSNP-containing immunity genes were enriched in the QTL regions associated with some economic traits for both breeds. Moreover, genetic changes involved in selective sweeps were detected. From the selective sweeps identified in our two breeds, several genes associated with growth, appetite, and metabolic regulation were identified. Our study provides a framework for genetic and genomic research of domestic chickens and facilitates the domestic chicken as an avian model for genomic, biomedical, and evolutionary studies.

Adjuvant effects of mannose-binding lectin ligands on the immune response to infectious bronchitis vaccine in chickens with high or low serum mannose-binding lectin concentrations

Mannose-binding lectin (MBL) plays a major role in the immune response as a soluble pattern-recognition receptor. MBL deficiency and susceptibility to different types of infections have been subject to extensive studies over the last decades. In humans and chickens, several studies have shown that MBL participates in the protection of hosts against virus infections. Infectious bronchitis (IB) is a highly contagious disease of economic importance in the poultry industry caused by the coronavirus infectious bronchitis virus (IBV). MBL has earlier been described to play a potential role in the pathogenesis of IBV infection and the production of IBV-specific antibodies, which may be exploited in optimising IBV vaccine strategies. The present study shows that MBL has the capability to bind to IBV in vitro. Chickens from two inbred lines (L10H and L10L) selected for high or low MBL serum concentrations, respectively, were vaccinated against IBV with or without the addition of the MBL ligands mannan, chitosan and fructooligosaccharide (FOS). The addition of MBL ligands to the IBV vaccine, especially FOS, enhanced the production of IBV-specific IgG antibody production in L10H chickens, but not L10L chickens after the second vaccination. The addition of FOS to the vaccine also increased the number of circulating CD4+ cells in L10H chickens compared to L10L chickens. The L10H chickens as well as the L10L chickens also showed an increased number of CD4-CD8α-γδ T-cells when an MBL ligand was added to the vaccine, most pronouncedly after the first vaccination. As MBL ligands co-administered with IBV vaccine induced differences between the two chicken lines, these results indirectly suggest that MBL is involved in the immune response to IBV vaccination. Furthermore, the higher antibody response in L10H chickens receiving vaccine and FOS makes FOS a potential adjuvant candidate in an IBV vaccine.

Immunity to bacterial infection in the chicken

Bacterial infections remain important to the poultry industry both in terms of animal and public health, the latter due to the importance of poultry as a source of foodborne bacterial zoonoses such as Salmonella and Campylobacter. As such, much focus of research to the immune response to bacterial infection has been to Salmonella. In this review we will focus on how research on avian salmonellosis has developed our understanding of immunity to bacteria in the chicken from understanding the role of TLRs in recognition of bacterial pathogens, through the role of heterophils, macrophages and γδ lymphocytes in innate immunity and activation of adaptive responses to the role of cellular and humoral immunity in immune clearance and protection. What is known of the immune response to other bacterial infections and in particular infections that have emerged recently as major problems in poultry production including Campylobacter jejuni, Avian Pathogenic Escherichia coli, Ornithobacterium rhinotracheale and Clostridium perfringens are discussed.

Chicken mannose-binding lectin (MBL) gene variants with influence on MBL serum concentrations

Mannose-binding lectin (MBL) plays a major role in the innate immune defence by activating the lectin complement pathway or by acting as an opsonin. Two forms of MBL have been characterised from several species, but for humans and chickens, only one form of functional MBL has been described. The human MBL2 gene is highly polymorphic, and it causes varying MBL serum levels. Several of the single-nucleotide polymorphisms (SNPs) have been associated with the severity of diseases of bacterial, viral or parasitic origin. Association between various diseases and different MBL serum levels has also been identified in chickens. In this study, two inbred chicken lines (L10L and L10H) which have been selected for low and high MBL levels in serum and four other experimental chicken lines were analysed for polymorphism in the MBL gene. The presence of polymorphisms in the MBL gene was revealed by southern blot analyses, and the differences in the serum concentrations of MBL were found to be of transcriptional origin according to real-time quantitative reverse transcription PCR analysis. Several SNPs were discovered in the promoter and the 5' untranslated region of the chicken MBL gene which resulted in the identification of six different alleles. Mapping of regulatory elements in the promoter region was performed, and SNPs that could affect the MBL serum concentration were identified. One SNP that was found to be located in a TATA box was altered in one of the six alleles only. This allele was associated with low MBL serum concentration.

Crosstalk between innate and adaptive immune responses to infectious bronchitis virus after vaccination and challenge of chickens varying in serum mannose-binding lectin concentrations

Mannose-binding lectin (MBL), a C-type collectin with structural similarities to C1q, is an innate pattern-recognition molecule that is sequestered to sites of inflammation and infections. MBL selectively binds distinct chemical patterns, including carbohydrates expressed on all kinds of pathogens. The present study shows that serum MBL levels influence the ability of chickens to clear the respiratory tract of virus genomes after an infectious bronchitis virus (IBV) infection. The primary IBV infection induced changes in circulating T-cell populations and in the specific antibody responses. Serum MBL levels also influenced IBV vaccine-induced changes in circulating T-cell populations. Moreover, addition of mannose to an IBV vaccine altered both vaccine-induced changes in circulating T-cell populations and IBV specific vaccine and infection-induced antibody responses in chickens with high serum MBL levels. These data demonstrate that MBL is involved in the regulation of the adaptive immune response to IBV.

Structural gene variants in the porcine mannose-binding lectin 1 (MBL1) gene are associated with low serum MBL-A concentrations

Mannose-binding lectin (MBL) is a collagenous lectin that kills a wide range of pathogenic microbes through complement activation. The MBL1 and MBL2 genes encode MBL-A and MBL-C, respectively. MBL deficiency in humans is associated with higher susceptibility to viral as well as bacterial infections. A number of single nucleotide polymorphisms (SNP) have been identified in the collagen-like domain of the human MBL gene, of which several are strongly associated with decreased concentrations of MBL in serum. In this study, we have identified a number of SNPs in the porcine MBL-A gene. Sequence comparisons identified a total of 14 SNPs, eight of which were found in exons and six in introns. Four of the eight exon-located SNPs were non-synonymous. Sequence data from several Duroc and Landrace pigs identified four different haplotypes. One haplotype was found in Duroc pigs only, and three haplotypes were found in the Landrace pigs. One of the identified haplotypes was associated with low concentration of MBL-A in serum. The concentration of MBL-A in serum was further assessed in a large number of Duroc and Landrace boars to address its correlation with disease frequency. The MBL-A concentration in Duroc boars showed one single population, whereas Landrace boars showed four distinct populations for MBL-A concentration. The Landrace boars were finally assessed for disease incidence, and the association with the concentration of MBL-A in serum was investigated. No association between MBL and disease incidence was found in this study.