Immunohistochemical investigation of the tissue distribution of mannan-binding lectin in non-infected and virus-infected chickens

Detection of low-load Epstein-Barr virus in blood samples by enriched recombinase aided amplification assay

Epstein-Barr virus (EBV), a common human γ-herpesvirus, infects more than 90% of adults worldwide. The purpose of this study was to establish a novel EBV detection method by combining the recombinase aided amplification (RAA) assay with an initial enrichment step that utilizes magnetic beads coated with a recombinant human mannan-binding lectin (rhMBL, M1 protein). An M1 protein–protein A magnetic bead complex (M1 beads) was prepared and used to achieve separation and enrichment of EBV from blood. After nucleic acid extraction, DNA was amplified by RAA. Using 388 whole blood samples and 1 serum sample, we explored the specificity, sensitivity and applicability of the newly developed detection method and compared it with commercial quantitative real-time polymerase chain reaction (qPCR) following M1 bead enrichment, traditional qPCR and traditional RAA. After enrichment, the positivity rate of EBV was increased from 15.94% to 17.74% by RAA (P < 0.05) and from 7.20% to 15.17% by qPCR (P < 0.05). The viral loads after enrichment were increased by 1.13 to 23.19-fold (P < 0.05). Our data demonstrates that an RAA assay incorporating M1 bead enrichment is a promising tool for detecting low EBV viral loads in blood samples that will facilitate an early response to EBV infection.

The RAA with an enrichment step that utilizes magnetic beads coated with M1 protein.

A very effective method for detecting low-load virus in blood samples.

The first report describing virus detection using this method.

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.

Chicken mannose binding lectin has antiviral activity towards infectious bronchitis virus

Mannose binding lectin (MBL) is a collagenous C-type lectin, which plays an important role in innate immunity. It can bind to carbohydrates on the surface of a wide range of pathogens, including viruses. Here we studied the antiviral effect of recombinant chicken (rc)MBL against Infectious Bronchitis Virus (IBV), a highly contagious coronavirus of chicken. rcMBL inhibited in a dose-dependent manner the infection of BHK-21 cells by IBV-Beaudette, as detected by immunofluorescence staining of viral proteins and qPCR. ELISA and negative staining electron microscopy showed that rcMBL bound directly to IBV, resulting in the aggregation of viral particles. Furthermore, we demonstrated that MBL bound specifically to the spike S1 protein of IBV which mediates viral attachment. This subsequently blocked the attachment of S1 to IBV-susceptible cells in chicken tracheal tissues as shown in protein histochemistry. Taken together, rcMBL exhibits antiviral activity against IBV, based on a direct interaction with IBV virions.

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 (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.

Mannan-binding lectin in children with chronic gastritis

The involvement of mannan-binding lectin (MBL) insufficiency in the pathogenesis of chronic gastritis (CG) in children was investigated. Blood samples were collected from 78 paediatric patients suffering from CG associated with Helicobacter pylori infection (group Hp(+)) and from 41 with the disease not associated with such an infection (group Hp(-)). Control group consisted of 77 children. The frequency of mbl-2 gene mutations and serum protein concentrations did not differ significantly in both groups as compared with controls. An expression of mbl-2 gene in gastric biopsies of CG patients was demonstrated. It was found to be stronger in H. pylori-infected children. The results presented in this paper suggest that MBL deficit/dysfunction probably does not contribute to an increased risk of CG (both associated and not associated with H. pylori infection) in children. However, MBL opsonic effect and/or the lectin pathway of complement activation may be taken into account as possible host defence mechanisms in gastric patients.

Mannan-binding lectin (MBL) in chickens: molecular and functional aspects

Mannan-binding lectin (MBL) is a serum collectin (i.e. mosaic protein with collagenous and lectin domains) involved in the innate immune defence against various microbes. In vitro studies indicate that MBL exerts its function by binding to the microbial surface through its carbohydrate recognition domains followed by direct opsonization or complement activation via the MBL associated serine proteases MASP-1 and MASP-2. In Aves (i.e. chickens), as in man, only one MBL form has been found, while traditional laboratory animals (i.e. mouse and rat) have two MBL forms in serum. MBL has been extensively studied in mammals but recently also in Aves. This review summarizes the present knowledge of MBL in chickens and compares it to the situation in mammals.

Serum levels of chicken mannan-binding lectin (MBL) during virus infections; indication that chicken MBL is an acute phase reactant

Mannan-binding lectin (MBL) is a serum collectin which is believed to be an opsonin of the innate immune defence against various microorganisms. MBL is a minor acute phase reactant in man. We investigated the concentration of serum MBL in chickens infected with infectious bronchitis virus (IBV) and infectious laryngotracheitis virus (ILTV). The concentration of serum MBL increased about twofold (from approximately 6 to 12 microg/ml) due to these viral infections. The concentration peaked 3-7 days after infection with IBV, and 3-5 days after ILTV infection, depending on the ILTV strain used. The increased levels returned to normal values 6-10 days after infection. The results indicated that MBL is a minor acute phase reactant in chickens.

Serum levels, ontogeny and heritability of chicken mannan-binding lectin (MBL)

Mannan-binding lectin (MBL) is a serum lectin found in mammals and recently also in birds. It is thought to play an important role in the innate immune defence through binding to surface carbohydrates on micro-organisms followed by complement activation via the MBL pathway. This results in opsonization or direct complement-mediated killing. To gain further knowledge about the physiology and function of the protein, we developed an enzyme-linked immunosorbent assay for chicken MBL and used this to investigate the level of MBL in different chicken strains during embryogenesis, early and adult life. The MBL concentrations in 308 chickens, representing 14 different strains, showed a non-Gaussian, unimodal distribution profile with a mean concentration of 5.8 micrograms/ml (range 0.4-37.8 micrograms/ml). No difference between the strains could be demonstrated and no chickens were found deficient in MBL. Ontogenetic studies showed that MBL is already detectable in embryos at a gestational age of 10 days (11 days before hatching). At hatching, the level is comparable to the level found in adult chickens. This level is fairly stable during the first weeks of life, but a deficiency state develops at 4 weeks of age, whereafter the level is normalized again at 5 weeks of age. Chickens with relatively low or high MBL levels were bred with cockerels having similar MBL levels and this resulted in F1 generations with significantly different MBL levels, suggesting that the protein level is genetically influenced.