Genomic structure and transcriptional regulation of the early B cell gene chB1

Identification and tissue-expression profiling of novel chicken c-type lectin-like domain containing proteins as potential targets for carbohydrate-based vaccine strategies

C-type lectin-like domain containing proteins (CTLDcps) mainly bind carbohydrate-based ligands, but also other ligands. CTLDcps are involved in several biological processes including cell adhesion, cell-cell interactions, and pathogen recognition. Pathogen recognition by myeloid cells, e.g. dendritic cells (DCs), can be facilitated through cell surface expressed CTLDcps. Cell surface expressed CTLDcps have been exploited in vaccine designs for specific targeting of human and mouse DCs using antibodies. In recent years, however, DC targeting using carbohydrate-based vaccines has gained interest due to low production cost, limited immunogenicity, and possibility of multivalent adjustment. In chicken, however, only a few CTLDcps have been identified. Identifying and annotating additional chicken CTLDcps (chCTLDcps) is needed to exploit carbohydrate-mediated DC targeting in chicken. Therefore, we searched the chicken GRCg6a assembly for novel chCTLDcps. We identified 28 chCTLDcps of which 10 had previously been described and also experimentally validated. RNA-seq and RT-qPCR confirmed mRNA expression of the remaining 18 identified chCTLDcps. A group of highly related chCTLDcps, moreover, was shown to be avian-specific and comprise novel members mapped to the proposed chicken natural killer gene complex. Two chCTLDcps, chCLEC17AL-A and chCLEC17AL-B, were found to share a recent common ancestor with CLEC17A. Putative mannose or fucose-binding sequence motifs, EPN and WND, were found in the CTLD of chCLEC17AL-A. Both contained intracellular internalisation and signalling sequence motifs. In conclusion, several chCTLDcps were identified and their expression confirmed. Both chCLEC17AL-A and -B showed promise as potential targets in carbohydrate-based chicken vaccine strategies. Determination of DC-specific expression of chCLEC17AL-A and -B, thus, might prove useful in chicken vaccinology.

Molecular mechanisms of primary and secondary mucosal immunity using avian infectious bronchitis virus as a model system

Although mucosal immune responses are critical for protection of hosts from clinical illness and even mortality caused by mucosal pathogens, the molecular mechanism of mucosal immunity, which is independent of systemic immunity, remains elusive. To explore the mechanistic basis of mucosal protective immunity, gene transcriptional profiling in mucosal tissues was evaluated after the primary and secondary immunization of animals with an attenuated avian infectious bronchitis virus (IBV), a prototype of Coronavirus and a well-characterized mucosal pathogen. Results showed that a number of innate immune factors including toll-like receptors (TLRs), retinoic-acid-inducible gene-1 (RIG-1), type I interferons (IFNs), complements, and interleukin-1 beta (IL-1β) were activated locally after the primary immunization. This was accompanied or immediately followed by a potent Th1 adaptive immunity as evidenced by the activation of T-cell signaling molecules, surface markers, and effector molecules. A strong humoral immune response as supported by the significantly up-regulated immunoglobulin (Ig) gamma chain was observed in the absence of innate, Th1 adaptive immunity, or IgA up-regulation after the secondary immunization, indicating that the local memory response is dominated by IgG. Overall, the results provided the first detailed kinetics on the molecular basis underlying the development of primary and secondary mucosal immunity. The key molecular signatures identified may provide new opportunities for improved prophylactic and therapeutic strategies to combat mucosal infections.

A novel avian homologue of CD72, chB1r, down modulates BCR-mediated activation signals

The avian B cell differentiation antigen chB1 is a C-type lectin membrane protein most homologous to mammalian CD72. Here, we report a new chB1-related gene, chB1r, that is located 18 kb away the chB1 gene. The cytoplasmic domain of chB1r protein contains two immunoreceptor tyrosine-based inhibitory motifs (ITIMs: ITIM1 and 2), which are identical to those found in CD72, whereas chB1 lacks the second ITIM2. Although chB1 expression is restricted to the bursa and an immature B cell line, chB1r is highly expressed in the bursa, spleen and both immature and mature B cell lines, a pattern that parallels CD72 expression. SHP-1 and Grb2 interact with phosphorylated tyrosine residues within chB1r ITIM1 and ITIM2, respectively. By contrast, ITIM1 of chB1 does not interact with SHP-1. Functional characterization using chB1r/chB1 double-deficient DT40 B cells demonstrated that ITIM1 in chB1r transduces a negative signal for BCR-mediated nuclear factor of activated T cells (NF-AT) activation and that ITIM2 attenuates this negative signal. This study has established chB1r as the genuine avian homologue of mammalian CD72, and revealed an opposing role for the two ITIMs through binding with SHP-1 and Grb2 for regulation of BCR-mediated NF-AT activation.

Cell-mediated immunity in poultry

In avian species, adaptive immunity involves both humoral and cell-mediated immune (CMI) responses. Although humoral or antibody-mediated immune responses are particularly effective against extracellular antigens, CMI responses are specialized in the elimination of intracellular antigens; the latter include those that have entered cells via the endocytic pathway (exogenous antigens; e.g., phagocytosed bacteria) or were produced within the cell such as viral proteins and proteins resulting from neoplastic transformation of the cell (endogenous antigens). CMI responses, like most humoral immune responses, are tightly regulated and require "help" from T helper cells, specifically the type 1 T helper cells (Th1, hence, the name Th1 responses). Th1 cells are characterized by their production of cytokines such as interferon-gamma (IFN-gamma), tumor-necrosis factor-alpha (TNF-alpha), and interleukin-2 that drive CMI responses. The functional effectors of CMI responses are various immune cells including cytotoxic lymphocytes (cytotoxic T cells and natural killer cells) and macrophages. Cytotoxic lymphocytes and macrophages are specialized in the elimination of endogenous and exogenous antigens, respectively. In the past decade, substantial progress has been made in defining the role and regulation of avian CMI responses. Other advances have addressed strategies that strengthen this arm of adaptive immunity to optimize defense as well as protection against neoplastic diseases and nonneoplastic diseases caused by intracellular pathogens.

Base usage and dinucleotide frequency of infectious bursal disease virus

Base usage and dinucleotide frequency have been extensively studied in many eukaryotic organisms and bacteria, but not for viruses. In this paper, a comprehensive analysis of these aspects for infectious bursal disease virus (IBDV) was presented. The analysis of base usage indicated that all of the IBDV genes possess equivalent overall nucleotide distributions. However when the base usage at each codon positions was analysed by using cluster analysis, the VP5 open reading frame (ORF) formed a different cluster isolated from the other genes. The unusual base usage of VP5 ORF may indicate that the gene was originated by the virus "overprinting strategy", a strategy in which virus may create novel gene by utilizing the unused reading frames of its existing genes. Meanwhile, the GC content of the IBDV genes and the chicken's coding sequences was comparable; suggesting the virus imitation of the host to increase its translational efficiency. The analysis of dinucleotide frequency indicated that IBDV genome had dinucleotide bias: the frequencies of CpG and TpA were lower and the TpG was higher than the expected. Classical methylation pathway, a process where CpG converted to TpG, may explain the significant correlation between the CpG deficiency and TpG abundance. "Principal component analysis of the dinucleotide frequencies" (DF-PCA) was used to analyse the overall dinucleotide frequencies of IBDV genome. DF-PCA on the hypervariable region and polyprotein (VPX-VP4-VP3) gene showed that the very virulent IBDV (vvIBDV) was segregated from other strains; which meant vvIBDV had a unique dinucleotide pattern. In summary, the study of base usage and dinucleotide frequency had unravelled many overlooked genomic properties of the virus.