Construction, Expression and Immunoassay Detection of Recombinant Plasmid Encoding Fusion Protein of Roman Chicken Complement C3d and Newcastle Disease Virus F gene

Cloning and structural analysis of complement component 3d in wild birds provides insight into its functional evolution

Complement component 3 d (C3d) is the final cleavage product of the complement component C3 and serves as a crucial role in link innate and adaptive immunity, and increase B-cell sensitivity to an antigen by 1000-10000 fold. The crystal structure of human C3d revealed there are two distinct surfaces, a convex surface containing the thioester-constituting residues that mediate covalent binding to the target antigen, and a concave surface with an acidic pocket responsible for interaction with CR2. In this study, we cloned and sequenced cDNA fragment encoding C3d region from 15 wild bird species. Then, the C3d sequences from wild birds, chicken and mammals were aligned to construct phylogenetic trees. Phylogenetic tree displayed two main branches, indicating mammals and birds, but the bird C3d branch was divided into two main parts, with five wild birds (Ardeola bacchus, Zoothera, Bubo, Crossoptilon mantchuricum and Caprimulgus europaeus) clustering much closer to mammals. In addition, the C3d proteins of Ardeola bacchus, Bubo, Crossoptilon mantchuricum and Caprimulgus europaeus contained a Glu163 residue at the position at which Lys163 was found in other birds. However, Glu163 have the same charge polarity as Asp163, which is the key amino acid residue comprising the acidic pocket combined with CR2 found at this position in mammals, and Zoothera also possessed Asp163 at this position. Structure modeling analyses also verified that the C3ds of these five wild bird species exhibited the amino acid sequence and structure comprising the typical acidic pocket found in mammals that is required for combination with B cell surface receptors, which contribute electrostatic forces to interact with CR2. Our investigations indicate that some bird C3ds may already have the ability to bind with CR2 by electrostatic force, like mammals. As Ardeola bacchus, Zoothera, Bubo, Crossoptilon mantchuricum and Caprimulgus europaeus have more typical C3d concave acid pockets and thus a stronger ability to bind CR2, we speculate that these five wild birds may have a solider immunity against pathogens. Our phylogenetic and structural analyses of bird C3ds provide insights on the evolutionary divergence in the function of immune factors of avian and mammalian.

Transcriptomes of whole blood and PBMC in chickens

Global transcriptome analysis of chicken whole blood to discover biomarkers of different phenotypes or physiological disorders has never been investigated so far. Whole blood provides significant advantages, allowing large scale and non-invasive sampling. However, generation of gene expression data from the blood of non-mammalian species remains a challenge, notably due to the nucleated red blood cells, hindering the use of well-established protocols. The aim of this study was to analyze the relevance of using whole blood cells (WB) to find biomarkers, instead of Peripheral Blood Mononuclear Cells (PBMC), usually chosen for immune challenges. RNA sources from WB and PBMC was characterized by microarray analysis. Our results show that the quality and quantity of RNA obtained from WB was suitable for further analyses, although the quality was lower than that from PBMC. The transcriptome profiling comparison revealed that the majority of genes were expressed in both WB and PBMC. Hemoglobin subunits were the major transcripts in WB, whereas the most enriched biological process was related to protein catabolic process. Most of the over-represented transcripts in PBMC were implicated in functions specific to thrombocytes, like coagulation and platelet activation, probably due to the large proportion of this nucleated cell type in chicken PBMC. Functions related to B and T cells and to other immune functions were also enriched in the PBMC subset. We conclude that WB is more suitable for large scale immunity oriented studies and other biological processes that have been poorly investigated so far.

Recombinant phosphoprotein based single serum dilution ELISA for rapid serological detection of Newcastle disease virus

Newcastle disease virus (NDV) is the causative agent of a highly contagious disease in avian species. All strains of NDV belong to avian paramyxovirus serotype-1. The disease is endemic in different parts of the world and vaccination is the only way to protect birds from NDV infection. The virus non-structural phosphoprotein (P) is the second most abundant protein and a major modulator of viral replication. Although P protein shows lesser evolutionary divergence among NDV isolates, it is known to be highly divergent among different avian paramyxovirus serotypes. In the present study, a recombinant P protein based single serum dilution ELISA was developed which showed better sensitivity, specificity and accuracy as compared to conventional methods for NDV detection. The recombinant P protein based ELISA could be an alternative to existing diagnostics against NDV infection in chickens.

C3d adjuvant activity is reduced by altering residues involved in the electronegative binding of C3d to CR2

The final degradation product of the complement protein C3, C3d, has been used as a molecular adjuvant to various antigens. Chimera proteins of the antigen and multiple copies of C3d were developed to test the adjuvant effect of this molecule. The main mechanism by which C3d enhances the immune response is interaction with CR2. In vitro studies showed that the avidity of C3d for CR2 is affected by residues located at the interacting surface (e.g. 170N) as well as by residues located in other areas. The role of the latter residues has been proposed to depend on the electrostatic nature of the C3d-CR2 interaction, where the charges of the whole molecules are responsible for their binding. C3d is primarily a negatively charged molecule, while CR2 is a positive one. Previous experiments demonstrated that elimination of a positive charge (K162A) in C3d enhanced its avidity for CR2, while elimination of negative charges or addition positives ones (D163A, N170R, respectively), impaired the avidity for CR2. Despite the extensive in vitro research, the role of these residues in the adjuvant effect of C3d is unclear. To study the role of residues at the interacting and non-interacting surface of C3d on the adjuvanticity, single as well as a double residue substitutions were engineered in the murine C3d (R162A, D163A, N170R and D163A-N170R) gene. Two copies of these mutant molecules were fused to HIV-1 Env(gp120) and the proteins were tested for their avidity to bind CR2 (sCR2). Later, these DNA constructs were tested in mice to determine their adjuvant capability. Mutation at residue 162 (R162A) neither enhanced nor impaired the avidity of Env(gp120)-C3d(2) for sCR2 in vitro. Mutations at residues D163A and N170R, on the other hand, reduced the binding affinity of Env(gp120)-C3d(2) for sCR2. Furthermore, these mutations synergized and abolished the interaction of C3d for CR2. The data correlated with the adjuvant capability of these molecules in the mouse model. In summary, residues that alter the electronegative status of C3d (D163A and N170R) impair the binding of chimera proteins to CR2, reducing the adjuvant activity of this molecule.