Biomedical subjects

John R Young

Publications and source records attributed to John R Young.

10 recordsLinked to original sources

PubMed2006

Diversified bursal medullary B cells survive and expand independently after depletion following neonatal infectious bursal disease virus infection.

The primary immunoglobulin repertoire of chickens is generated not by gene rearrangement but by a subsequent process of gene conversion in proliferating immature B cells within the follicles of a specialized gut-associated lymphoid organ, the bursa of Fabricius. Neonatal infection with infectious bursal disease virus can eliminate almost the entire bursal B-cell compartment. Thereafter, two types of follicle reappear. Larger follicles, with rapidly proliferating B cells and normal structure, are correlated with partial recovery of antibody response. Smaller follicles, lacking distinct cortex and medulla, appear unable to produce antigen-responsive B cells. To understand the genesis of the two types of follicle, we analysed their VL sequences and activation-induced deaminase mRNA levels. The results provide a model of bursal repopulation in which surviving bursal stem cells generate new follicles with normal morphology and function, while surviving medullary B cells continue to proliferate slowly, under the influence of stromal cells, giving rise to the smaller follicles. The latter remain fixed in a stage of development incapable of further gene diversification.

Animals↗

PubMed2006

Transcriptional profiling reveals a possible role for the timing of the inflammatory response in determining susceptibility to a viral infection.

Using a novel cDNA microarray prepared from sources of actively responding immune system cells, we have investigated the changes in gene expression in the target tissue during the early stages of infection of neonatal chickens with infectious bursal disease virus. Infections of two lines of chickens previously documented as genetically resistant and sensitive to infection were compared in order to ascertain early differences in the response to infection that might provide clues to the mechanism of differential genetic resistance. In addition to major changes that could be explained by previously described changes in infected tissue, some differences in gene expression on infection, and differences between the two chicken lines, were observed that led to a model for resistance in which a more rapid inflammatory response and more-extensive p53-related induction of apoptosis in the target B cells might limit viral replication and consequent pathology. Ironically, the effect in the asymptomatic neonatal infection is that more-severe B-cell depletion is seen in the more genetically resistant chicken. Changes of expression of many chicken genes of unknown function, indicating possible roles in the response to infection, may aid in the functional annotation of these genes.

Animals↗

PubMed2005

Conservation of biological properties of the CD40 ligand, CD154 in a non-mammalian vertebrate.

Signals delivered by the CD40 ligand, CD154, have crucial roles in immune responses in mammals, being required for development of germinal centres, maturation of T-dependent antibody responses, and generation of B-cell memory. To determine whether these functions were conserved in a non-mammalian species, a putative chicken CD 154 cDNA was used to make an oligomeric fusion protein, and to raise monoclonal antibodies. The antibodies detected surface expression on activated T-cells. The fusion protein detected expression of a receptor on B-cells, thrombocytes and macrophages. Biological effects of the fusion protein included induction of NO synthesis in a macrophage cell line, enhancement of splenic B-cell survival, and induction of apoptosis in a bursal lymphoma cell line. These observations demonstrated substantial functional equivalence with mammalian CD 154 and thus provided evidence for the early evolutionary emergence of the set of functions associated with this molecule, and its central role in the vertebrate immune system.

Amino Acid Sequence↗

PubMed2005

A genomic analysis of chicken cytokines and chemokines.

As most mechanisms of adaptive immunity evolved during the divergence of vertebrates, the immune systems of extant vertebrates represent different successful variations on the themes initiated in their earliest common ancestors. The genes involved in elaborating these mechanisms have been subject to exceptional selective pressures in an arms race with highly adaptable pathogens, resulting in highly divergent sequences of orthologous genes and the gain and loss of members of gene families as different species find different solutions to the challenge of infection. Consequently, it has been difficult to transfer to the chicken detailed knowledge of the molecular mechanisms of the mammalian immune system and, thus, to enhance the already significant contribution of chickens toward understanding the evolution of immunity. The availability of the chicken genome sequence provides the opportunity to resolve outstanding questions concerning which molecular components of the immune system are shared between mammals and birds and which represent their unique evolutionary solutions. We have integrated genome data with existing knowledge to make a new comparative census of members of cytokine and chemokine gene families, distinguishing the core set of molecules likely to be common to all higher vertebrates from those particular to these 300 million-year-old lineages. Some differences can be explained by the different architectures of the mammalian and avian immune systems. Chickens lack lymph nodes and also the genes for the lymphotoxins and lymphotoxin receptors. The lack of functional eosinophils correlates with the absence of the eotaxin genes and our previously reported observation that interleukin- 5 (IL-5) is a pseudogene. To summarize, in the chicken genome, we can identify the genes for 23 ILs, 8 type I interferons (IFNs), IFN-gamma, 1 colony-stimulating factor (GM-CSF), 2 of the 3 known transforming growth factors (TGFs), 24 chemokines (1 XCL, 14 CCL, 8 CXCL, and 1 CX3CL), and 10 tumor necrosis factor superfamily (TNFSF) members. Receptor genes present in the genome suggest the likely presence of 2 other ILs, 1 other CSF, and 2 other TNFSF members.

Amino Acid Sequence↗

PubMed2005

Infectious bursal disease virus-induced immunosuppression in the chick is associated with the presence of undifferentiated follicles in the recovering bursa.

Infectious bursal disease virus (IBDV) causes an acute cytolytic infection in chicken B lymphocytes resulting in destruction of the B-cell population. Most severe depletion occurs in the bursa of Fabricius, where the immunoglobulin repertoire is developed by gene conversion. Chicks surviving IBDV infection are immunosuppressed despite repopulation of the bursa with B cells. Here we show that infection of neonatal chicks with a classical virulent IBDV strain (F52/70) causes severe bursal Bcell depletion with recovery after about one week. Two distinct types of bursal follicles developed: large reconstituted follicles and small poorly developed follicles lacking a discernible cortex and medulla. The presence of large numbers of undifferentiated follicles was associated with inability to mount antibody responses to IBDV itself and after immunization with Salmonella Enteritidis bacterin, indicating that B cells in these follicles are unable to produce peripheral B-cells with an effective immunoglobulin repertoire. Additionally a number of inflammatory foci were observed in the recovering bursa. These foci contained few B cells at the margins, but large numbers of CD4(+) and CD8(+) cells, scattered gammadelta(+) T-cells and macrophages, and small central aggregates of dendriticlike cells expressing the CD40 antigen.

Animals↗

PubMed2004

Developmentally programmed expression of AID in chicken B cells.

In mice, activation induced deaminase, AID, is expressed only in germinal center B cells. It is required for the initiation of somatic hypermutation and class switch recombination. In chickens and most mammals immunoglobulin gene rearrangement generates limited diversity and the primary immunoglobulin repertoire depends on subsequent somatic hypermutation or gene conversion. Immunoglobulin gene conversion in chickens starts in the embryonic bursa, before antigen exposure. The demonstrated requirement for AID for gene conversion in the bursal lymphoma cell line, DT40, implies developmental regulation of AID expression. To test this prediction, we examined the timing and location of AID mRNA expression. An abrupt increase in AID mRNA coincided with the onset of extensive Ig gene conversion in the bursa. Expression was also detected at earlier stages, implying either that expression of AID is not the only controlling factor for gene conversion, or that gene conversion can precede the formation of bursal follicles.

Animals↗

PubMed2004

A genetic variation map for chicken with 2.8 million single-nucleotide polymorphisms.

We describe a genetic variation map for the chicken genome containing 2.8 million single-nucleotide polymorphisms (SNPs). This map is based on a comparison of the sequences of three domestic chicken breeds (a broiler, a layer and a Chinese silkie) with that of their wild ancestor, red jungle fowl. Subsequent experiments indicate that at least 90% of the variant sites are true SNPs, and at least 70% are common SNPs that segregate in many domestic breeds. Mean nucleotide diversity is about five SNPs per kilobase for almost every possible comparison between red jungle fowl and domestic lines, between two different domestic lines, and within domestic lines--in contrast to the notion that domestic animals are highly inbred relative to their wild ancestors. In fact, most of the SNPs originated before domestication, and there is little evidence of selective sweeps for adaptive alleles on length scales greater than 100 kilobases.

Alleles↗

PubMed2004

Cloning and characterization of chicken IL-10 and its role in the immune response to Eimeria maxima.

We isolated the full-length chicken IL-10 (chIL-10) cDNA from an expressed sequence tag library derived from RNA from cecal tonsils of Eimeria tenella-infected chickens. It encodes a 178-aa polypeptide, with a predicted 162-aa mature peptide. Chicken IL-10 has 45 and 42% aa identity with human and murine IL-10, respectively. The structures of the chIL-10 gene and its promoter were determined by direct sequencing of a bacterial artificial chromosome containing chIL-10. The chIL-10 gene structure is similar to (five exons, four introns), but more compact than, that of its mammalian orthologues. The promoter is more similar to that of Fugu IL-10 than human IL-10. Chicken IL-10 mRNA expression was identified mainly in the bursa of Fabricius and cecal tonsils, with low levels of expression also seen in thymus, liver, and lung. Expression was also detected in PHA-activated thymocytes and LPS-stimulated monocyte-derived macrophages, with high expression in an LPS-stimulated macrophage cell line. Recombinant chIL-10 was produced and bioactivity demonstrated through IL-10-induced inhibition of IFN-gamma synthesis by mitogen-activated lymphocytes. We measured the expression of mRNA for chIL-10 and other signature cytokines in gut and spleen of resistant (line C.B12) and susceptible (line 15I) chickens during the course of an E. maxima infection. Susceptible chickens showed higher levels of chIL-10 mRNA expression in the spleen, both constitutively and after infection, and in the small intestine after infection than did resistant chickens. These data indicate a potential role for chIL-10 in changing the Th bias during infection with an intracellular protozoan, thereby contributing to susceptibility of line 15I chickens.

Amino Acid Sequence↗

PubMed2002

The chicken CD4 gene has remained conserved in evolution.

CD4 has a central role in thymocyte differentiation and cell-mediated immunity. We isolated and analyzed chicken CD4. The gene spans 11.5 kb and is composed of ten exons. The promoter is TATA-less and similar to the mouse and human CD4 promoters, with two transcription start sites as determined by 5'RACE analysis. In general the introns are short, although the 5'untranslated region includes a large intron of 5.6 kb containing binding sites of the putative CD4 silencer. The single-strand conformation polymorphism technique was used to identify a polymorphism to map the gene, which lies on chicken Chromosome 1 in a position showing conserved synteny to mouse and human. This is the first report describing the organization of CD4 from a non-mammalian species. The structure and localization of chicken CD4 and many sequence motifs important in its regulation have remained conserved during evolution.

Animals↗

PubMed2002

Uncertainty and conservatism in assessing environmental impact under paragraph 316(b): lessons from the Hudson River case.

Initially, regulation of cooling water intakes under paragraph 316(b) was extremely conservative due to the rapid increase predicted for generating capacity, and to the uncertainty associated with our knowledge of the effects of entrainment and impingement. The uncertainty arose from four main sources: estimation of direct plant effects; understanding of population regulatory processes; measurement of population parameters; and predictability of future conditions. Over the last quarter-century, the uncertainty from the first three sources has been substantially reduced, and analytical techniques exist to deal with the fourth. In addition, the dire predictions initially made for some water bodies have not been realized, demonstrating that populations can successfully withstand power plant impacts. This reduced uncertainty has resulted in less conservative regulation in some, but not all venues. New York appears to be taking a more conservative approach to cooling water intakes. The conservative approach is not based on regulations, but in a philosophy that power plant mortality is an illegitimate use of the aquatic resources. This philosophy may simplify permitting decisions, but it does not further the development of a science-based definition of adverse environmental impact.

Animals↗