Molecular genetics of the chicken MHC: current status and evolutionary aspects

Molecular Characterization of MHC Class I Genes in Four Species of the Turdidae Family to Assess Genetic Diversity and Selection

In vertebrate animals, the molecules encoded by major histocompatibility complex (MHC) genes play an essential role in the adaptive immunity. MHC class I deals with intracellular pathogens (virus) in birds. MHC class I diversity depends on the consequence of local and global environment selective pressure and gene flow. Here, we evaluated the MHC class I gene in four species of the Turdidae family from a broad geographical area of northeast China. We isolated 77 MHC class I sequences, including 47 putatively functional sequences and 30 pseudosequences from 80 individuals. Using the method based on analysis of cloned amplicons (n = 25) for each species, we found two and seven MHC I sequences per individual indicating more than one MHC I locus identified in all sampled species. Results revealed an overall elevated genetic diversity at MHC class I, evidence of different selection patterns among the domains of PBR and non-PBR. Alleles are found to be divergent with overall polymorphic sites per species ranging between 58 and 70 (out of 291 sites). Moreover, transspecies alleles were evident due to convergent evolution or recent speciation for the genus. Phylogenetic relationships among MHC I show an intermingling of alleles clustering among the Turdidae family rather than between other passerines. Pronounced MHC I gene diversity is essential for the existence of species. Our study signifies a valuable tool for the characterization of evolutionary relevant difference across a population of birds with high conservational concerns.

Effective population sizes and adaptive genetic variation in a captive bird population

Captive populations are considered a key component of ex situ conservation programs. Research on multiple taxa has shown the differential success of maintaining demographic versus genetic stability and viability in captive populations. In typical captive populations, usually founded by few or related individuals, genetic diversity can be lost and inbreeding can accumulate rapidly, calling into question their ultimate utility for release into the wild. Furthermore, domestication selection for survival in captive conditions is another concern. Therefore, it is crucial to understand the dynamics of population sizes, particularly the effective population size, and genetic diversity at non-neutral and adaptive loci in captive populations. In this study, we assessed effective population sizes and genetic variation at both neutral microsatellite markers, as well as SNP variants from the MHC-B locus of a captive Red Junglefowl population. This population represents a rare instance of a population with a well-documented history in captivity, following a realistic scenario of chain-of-custody, unlike many captive lab populations. Our analyses, which included 27 individuals comprising the entirety of one captive population show very low neutral and adaptive genetic variation, as well as low effective sizes, which correspond with the known demographic history. Finally, our study also shows the divergent impacts of small effective size and inbreeding in captive populations on microsatellite versus adaptive genetic variation in the MHC-B locus. Our study provides insights into the difficulties of maintaining adaptive genetic variation in small captive populations.

Diversity of Mhc class I and IIB genes in house sparrows (Passer domesticus)

In order to understand the expression and evolution of host resistance to pathogens, we need to examine the links between genetic variability at the major histocompatibility complex ( Mhc), phenotypic expression of the immune response and parasite resistance in natural populations. To do so, we characterized the Mhc class I and IIB genes of house sparrows with the goal of designing a PCR-based genotyping method for the Mhc genes using denaturing gradient gel electrophoresis (DGGE). The incredible success of house sparrows in colonizing habitats worldwide allows us to assess the importance of the variability of Mhc genes in the face of various pathogenic pressures. Isolation and sequencing of Mhc class I and IIB alleles revealed that house sparrows have fewer loci and fewer alleles than great reed warblers. In addition, the Mhc class I genes divided in two distinct lineages with different levels of polymorphism, possibly indicating different functional roles for each gene family. This organization is reminiscent of the chicken B complex and Rfp-Y system. The house sparrow Mhc hence appears to be intermediate between the great reed warbler and the chicken Mhc, both in terms of numbers of alleles and existence of within-class lineages. We specifically amplified one Mhc class I gene family and ran the PCR products on DGGE gels. The individuals screened displayed between one and ten DGGE bands, indicating that this method can be used in future studies to explore the ecological impacts of Mhc diversity.

The properties of the single chicken MHC classical class II alpha chain ( B-LA) gene indicate an ancient origin for the DR/E-like isotype of class II molecules

In mammals, there are MHC class II molecules with distinctive sequence features, such as the classical isotypes DR, DQ and DP. These particular isotypes have not been reported in non-mammalian vertebrates. We have isolated the class II (B-L) alpha chain from outbred chickens as the basis for the cloning and sequencing of the cDNA. We found only one class II alpha chain transcript, which bears the major features of a classical class II alpha sequence, including the critical peptide-binding residues. The chicken sequence is more similar to human DR than to the DQ, DP, DO or DM isotypes, most significantly in the peptide-binding alpha(1) domain. The cDNA and genomic DNA sequences from chickens of diverse origins show few alleles, which differ in only four nucleotides and one amino acid. In contrast, significant restriction fragment length polymorphism is detected by Southern blot analysis of genomic DNA, suggesting considerable diversity around the gene. Analysis of a large back-cross family indicates that the class II alpha chain locus ( B-LA) is located roughly 5.6 cM from the MHC locus, which encodes the classical class II beta chains. Thus the chicken class II alpha chain gene is like the mammalian DR and E isotypes in three properties: the presence of the critical peptide-binding residues, the low level of polymorphism and sequence diversity, and the recombinational separation from the class II beta chain genes. These results indicate that the sequence features of this lineage are both functionally important and at least 300 million years old.

Sequence comparison of avian interferon regulatory factors and identification of the avian CEC-32 cell as a quail cell line

Interferon (IFN) regulatory factor-1 (IRF-1) is a well-characterized member of the IRF family. Previously, we have cloned cDNA of several members of the chicken IRF (ChIRF) family and studied the function of ChIRF-1 in the avian cell line CEC-32. The IRF-1 proteins from primary chicken embryo fibroblasts (CEF) and CEC-32 cells differed in their electrophoretic mobility. To characterize the different forms of IRF-1 in avian cells, we compared the sequences of IRF-1 cDNA from CEC-32 cells, primary CEF, and quail fibroblasts (QEF). The deduced amino acid sequences of IRF-1 cDNA from chicken and quail show high similarity. Comparison of genomic sequences of IRF-1 and IFN consensus sequence binding protein (ICSBP) also confirm the relatedness of the members of the IRF family in quail and chicken. Based on these data, it is concluded that the avian fibroblast cell line CEC-32 is derived from quail. This conclusion is further supported by deoxynucleotide sequence comparison of a DNA fragment in an avian MHC class II gene and by fluorescence in situ hybridization (FISH) using the vertebrate telomeric (TTAGGG) repeat. Chromosome morphology and the lack of interstitial hybridization signals in macrochromosomes suggest that the CEC-32 cell line has probably been derived from Japanese quail.

Major histocompatibility complex (MHC) related cDNA probes associated with antibody response in meat-type chickens

The major histocompatibility complex (MHC) region was examined as a set of candidate genes for association between DNA markers and antibody response. Intercross F2 families of chickens were generated from a cross between high (HC) and low (LC) Escherichia coli(i) antibody lines. Restriction fragment length polymorphism (RFLP) analysis was conducted by using three MHC-related cDNA probes: chicken MHC class IV (B-G), chicken MHC class I (B-F), and human MHC-linked Tap2. Association between RFLP bands and three antibody response traits (E. coli, sheep red blood cells and Newcastle disease virus) were determined by two methods: by statistically analyzing each band separately and also by analyzing all bands obtained from the three probes by using multiple regression analysis to account for the multiple comparisons. The MHC class IV probe was the highest in polymorphisms but had the lowest number of bands associated with antibody response. The MHC class I probe yielded 15 polymorphic bands of which four exhibited association with antibody response traits. The Tap2 probe yielded 20 different RFLP bands of which five were associated with antibody production. Some Tap2 bands were associated with multiple antibody response traits. The multiband analysis of the three probes' bands revealed more significant effects than the analysis of each band separately. This study illustrates the efficacy of using multiple MHC region probes as candidate markers for quantitative trait loci (QTLs) controlling antibody response in chickens.

Coding sequences of the MHC II beta chain of homozygous rainbow trout (Oncorhynchus mykiss)

Six lines of homozygous rainbow trout (Oncorhynchus mikiss) from different genetic and geographical backgrounds have been produced as aquatic models for biomedical research by the chromosome set manipulation techniques of androgenesis and gynogenesis. Messenger RNA from spleens was extracted. and the MHC II B cDNA sequences, amplified by RT PCR, were cloned into plasmids. Sequences of the MHC II beta2 domains were highly conserved between the different plasmids from the same and different lines of trout. Most of the variability among sequences was found in the amino terminal half of the beta1 domain, which corresponds with the peptide binding region of the MHC II molecule. This diversity suggests that the different lines of trout may exhibit differences in immune response. Rainbow trout MHC II B sequences were similar to the MHC II B sequences of the Pacific salmon (O. gorbuscha, O. tshawytscha, O. nerka, O. miasou, O. kisutch). Southern blot analysis performed on the restricted DNA of the OSU and Hot Creek trout, and the doubled haploid progeny produced by androgenesis from OSU x Hot Creek hybrids indicates that two distinct genes encode the MHC II B sequences and that these genes are unlinked.

Assignment of Rfp-Y to the chicken major histocompatibility complex/NOR microchromosome and evidence for high-frequency recombination associated with the nucleolar organizer region

Rfp-Y is a second region in the genome of the chicken containing major histocompatibility complex (MHC) class I and II genes. Haplotypes of Rfp-Y assort independently from haplotypes of the B system, a region known to function as a MHC and to be located on chromosome 16 (a microchromosome) with the single nucleolar organizer region (NOR) in the chicken genome. Linkage mapping with reference populations failed to reveal the location of Rfp-Y, leaving Rfp-Y unlinked in a map containing >400 markers. A possible location of Rfp-Y became apparent in studies of chickens trisomic for chromosome 16 when it was noted that the intensity of restriction fragments associated with Rfp-Y increased with increasing copy number of chromosome 16. Further evidence that Rfp-Y might be located on chromosome 16 was obtained when individuals trisomic for chromosome 16 were found to transmit three Rfp-Y haplotypes. Finally, mapping of cosmid cluster III of the molecular map of chicken MHC genes (containing a MHC class II gene and two rRNA genes) to Rfp-Y validated the assignment of Rfp-Y to the MHC/NOR microchromosome. A genetic map can now be drawn for a portion of chicken chromosome 16 with Rfp-Y, encompassing two MHC class I and three MHC class II genes, separated from the B system by a region containing the NOR and exhibiting highly frequent recombination.

The telomeric and centromeric ends of HLA class I: MCD maps of YAC derived cosmids and sequence analysis of 740 kb of genomic DNA

We previously isolated and characterized a set of overlapping yeast artificial chromosome (YAC) clones spanning 2.4 Mb, including the entire MHC class I region, as a first step towards a detailed genetic analysis. We report here the genomic sequence of the two ends of HLA class I. The centromeric portion of HLA class I, extending from TNF to HLA-C was determined using two different sources of genomic DNA. As a first source, we sequenced cosmids (provided by T. Spies) derived from a total human DNA library which were mapped with conventional restriction digestion and fingerprinting. A second more generalizable approach was used to obtain cosmids for the remainder of the region. The new technology of Multiple-Complete-Digest (MCD) mapping, developed in Maynard Olson's laboratory, was used to map cosmids derived from YACs. This technique involves screening deep cosmid libraries derived from selected YACs and subjecting the cosmids to complete digestion with restriction enzymes, followed by computational assembly into completed maps. This method was also used to obtain material for sequence from three overlapping YACs covering a contiguous region from HLA-G to a point 330 kb telomeric. Among the plethora of new genetic information is a detailed picture of the organization of new multigene families contained within the telomeric end and of members of families spread throughout HLA class I. A clear relationship between the telomeric and centromeric ends of HLA class I has been defined, suggesting that large portions of these regions derived from a common ancestor. Our results demonstrate genomic sequencing to be one of the most effective and efficient means of identifying new genes, yielding information about genomic structure, regulation, and offering new insights into the meaning of physical relationships among functionally interacting genes.

Dynamics of Mhc evolution in birds and crocodilians: amplification of class II genes with degenerate primers

Genes of the major histocompatibility complex (Mhc) are the most polymorphic functional loci in mammalian populations, but little is known of Mhc variability in natural populations of nonmammalian vertebrates. To help extend such studies to birds and relatives, we present a pair of degenerate primers that amplify polymorphic segments of one chain (the beta chain) of the class II genes from the major histocompatibility complex (Mhc) of archosaurs (birds+crocodilians). The primers target two conserved regions lying within portions of the antigen-binding site (ABS) encoded by the second exon and amplify multiple genes from both genomic DNA and cDNA. The pattern of nucleotide substitution in ABS codons of 51 sequences amplified and cloned from five species of passerine birds and an alligator (Alligator mississippiensis) indicates that archosaurian class II beta genes are subject to selective forces similar to those operating in mammalian populations. Hybridization of a genomic clone generated by the primers revealed highly polymorphic bands in a sample of Florida scrub jays (Aphelocoma coerulescens coerulescens). Because the primers amplify only part of the ABS from multiple class II genes, they will be useful primarily for generating species specific clones, thereby providing a critical inroad to more detailed structural and evolutionary studies.

Selective expression of major histocompatibility complex (MHC) antigens and modulation of T-cell differentiation in chickens with increased MHC-chromosome dosages

Increased dosage of genes belonging to the immunoglobulin superfamily may be responsible for some of the less noticeable but targeted phenotypic disturbances seen in trisomy conditions of humans and animals. We used an avian aneuploidy model to study the specific effects of extra major histocompatibility complex (MHC)-microchromosome dosage on the progression of thymocyte differentiation through a broad period of embryonic and neonatal development. The particular goal in the present investigation was to determine whether a reduction in the number of thymocytes, previously observed in the developing thymus of MHC aneuploids, is accompanied by particular alterations in thymocyte differentiation. We hypothesized that the subpopulation structure and/or developmental pattern for thymocyte differentiation are characteristically perturbed (delayed or modified) by increased MHC-chromosome dosage in cells. The regulation of MHC surface antigen expression in aneuploid thymocytes was also studied to detect dosage-dependent expression for one and possibly more sub-regions (class I, II, IV) of the avian MHC. Surface densities of MHC class I antigens on thymocytes were increased significantly at all ages studied, for example by 15% and 45% in trisomics and tetrasomics, respectively at 22 days post-hatching. The surface density of CT1 antigen, a thymocyte-specific marker, was also increased in a dosage-dependent manner, but only in juveniles. Increases in the proportion of alpha beta 1, TCR+ and CD3+ thymocytes were observed in juveniles, with no alterations in other TCR-expressing thymocytes. No major alterations in CD4 and CD8 thymocyte populations were observed. These results demonstrate a targeted effect of extra MHC-chromosome dosage towards enhanced class I and CT1, and not class II or IV, expression. The increased MHC-microchromosome dosage appears to influence primarily immature thymocytes expressing alpha beta 1 TCR and CD3.

Genetic analysis of three loci homologous to human G9a: evidence for linkage of a class III gene with the chicken MHC

The cDNA clones of two newly discovered genes in the class III region of the human major histocompatibility complex (MHC) were hybridized to chicken DNA. One of these cDNA clones (pG9a-4C7), which detects the single-copy human G9a (BAT8) gene, gave a repeatable restriction pattern. This heterologous cDNA clone was used to detect and map three different PstI restriction fragment length polymorphisms among the two internationally recognized chicken reference populations. Two of the loci were unlinked to previously mapped markers, but one polymorphism cosegregated with the EaB locus in the Compton mapping population. These results provide evidence that some genes of the mammalian class III region, such as G9a, may be linked to the MHC in chickens.

Complete coding sequence of rainbow trout Mhc II beta chain

Several cDNA clones comprising the entire coding sequence of the rainbow trout (Oncorhynchus mykiss) major histocompatibility comlex (Mhc) class II B gene have been isolated from different sources. A single B gene appears to be transcribed in the rainbow trout and it encodes a 247 amino acid long polypeptide, which is of similar size to mammalian, avian, and amphibian and other teleost beta chains. The amino acid sequence identity to mammalian, amphibian, and avian class II beta chains is only about 30%. Despite the low similarity, a striking pattern of conservation is observed, both in the putative peptide-binding domain and in the Ig-like domain. Most of the conserved residues are located in the Ig-like domain and in the transmembrane segment. The majority of polymorphic residues reside in the beta 1 domain, with the greatest variability found in the amino-terminal half of the domain. The sequence data are compatible with a rather limited polymorphism of a single, expressed Mhc class II B gene.

Two Mhc class I and two Mhc class II genes map to the chicken Rfp-Y system outside the B complex

Gene sequences highly similar to major histocompatibility complex (Mhc) class I and class II genes were recently recognized as mapping to a site in the genome of the chicken separate from the Mhc class I, class II, and B-G genes of the major histocompatibility (B) complex. The present study was undertaken to see whether this complex of Mhc-like genes designated as restriction fragment pattern Y (Rfp-Y) might reside in one of three clusters of cosmid clones contained within the molecular map of chicken Mhc genes, since only two of the three clusters can be assigned to the B system. To determine whether the third cluster (cluster II/IV) might contain Rfp-Y, a subclone (18.1) from within cluster II/IV near a polymorphic lectin gene was used to analyze the DNA of families in which Rfp-Y haplotypes are known to be segregating. The restriction fragment polymorphisms revealed by the 18.1 probe were found to segregate in parallel with the restriction fragment polymorphisms defining the Rfp-Y haplotypes, thus establishing the location of Rfp-Y within cosmid cluster II/IV. Two of six Mhc class I genes and two of five Mhc class II genes map to cosmid cluster II/IV, so a substantial fraction of chicken Mhc genes, including at least one that may be expressed, are located in a chromosomal region separate from the B system. In further linkage analyses, Rfp-Y was found to assort independently from more than 400 markers in the present linkage map of the chicken genome.

The marsupial MHC: the tammar wallaby, Macropus eugenii, contains an expressed DNA-like gene on chromosome 1

In the placental mammal major histocompatibility complex (MHC) three main families of class II genes, DR, DQ, and DP, have been recognized. Each family contains genes that code for one or more A- and B-chains. Recent evidence has indicated that a fourth family can be described, the DN/DO family. These four families arose sometime early in mammalian evolution. Our purpose was to deduce the MHC of an early mammalian ancestor of marsupials and eutherians. Using primers designed to conserved regions in exon 2 and exon 3 of the DQA gene we amplified an 830-bp band from the total genomic DNA of the marsupial, Macropus eugenii (tammar wallaby). However, sequence analysis of cloned genomic products showed that the primers had amplified three genes, two of which appeared to be alleles at one locus, while the other gene belonged to a closely related locus. Phylogenetic analysis showed that both these loci were most closely related to the human (HLA-DNA) and mouse (H-20a) DNA genes, with a bootstrap support of 78%. Expression of only one locus could be detected by RT-PCR from spleen RNA. In situ hybridization to tammar wallaby chromosomes mapped these genes to one region on the long arm of chromosome 1, indicating the position of the MHC in marsupials. Related A-chain genes were detected in monotremes, and human by southern blotting, and very faint bands were observed in the chicken. Hybridization with a tammar DNA-like gene on several marsupial species showed evidence of at least three DNA-like loci in the tammar wallaby, at least one in the koala, but none in the kowari. This indicates that the organization of the class II MHC may be more dynamic in marsupial than in placental mammals, but, in contrast to a previous study on the MHC of a marsupial, we cannot conclude that the class II gene families of placental and marsupial mammals evolved from different ancestral genes.

A class I cDNA from SPAFAS line-11 chickens

A chicken MHC class I (B-F) cDNA from SPAFAS line 11 embryonic liver tissue was isolated and characterized by nucleotide sequencing. Comparing this sequence with previously described B-F cDNAs highlights clustered nucleotide substitutions in exon 3, encoding amino acids located on the alpha-helical region of the alpha 2 domain.

Identification of class II major histocompatibility complex polymorphisms predicted to be important in peptide antigen presentation

Chickens of the B2, B5, B15, B19, and B21 B-congenic haplotypes differ in disease resistance. Complementary DNA from B-congenic chicken strains have been analyzed for allelic diversity of expressed Class II MHC genes. The predicted amino acid sequences of eight genes from five haplotypes were subjected to Wu-Kabat variability analysis. The B-L gene polymorphic regions and conserved regions are highly similar to the human leukocyte antigen Class II genes. Therefore, the present analysis reveals candidate polymorphisms important in determining the spectrum of antigenic peptides presented to T helper cells, and allelic differences possibly important in resistance to avian disease.

Influence of different B-complex recombinants on the outcome of Rous sarcomas in chickens

Seven major histocompatibility (B) complex recombinants were evaluated for anti-Rous sarcoma response. In experiment 1, the BR5(F21-G19) recombinant haplotype both homozygous and in heterozygous combinations with B19 and B21 haplotypes were compared to B19/B19 and B21/B21 chickens to determine the relative influence of the BF versus BG chromosomal segments on regression of Rous sarcoma virus-induced tumours. In experiment 2, six recombinant haplotypes BR1(F24-G23), BR2(F2-G23), BR3(F2-G23), BR4(F2-G23), BR6(F21-G23) and BR8(F2-G2a,23) present in chickens heterozygous for normal haplotypes B19, B23 or B26 were compared for anti-sarcoma response. A total of 1328 chickens were blood typed for B alloantigens at 17 days of age, inoculated in the wingweb with Rous sarcoma virus at 6 weeks and monitored for anti-tumour immune response over a 10-week period. Genotypes which shared the same BF haplotype, but differed in their BG regions, had similar anti-tumour responses, implicating the BF but not the BG region in tumour regression. Chickens carrying BF2 or BF21 had a strong anti-tumour response, while BF24 conferred a weaker response, regardless of the accompanying normal haplotype.

The turkey major histocompatibility complex: characterization by mixed lymphocyte, graft-versus-host splenomegaly, and skin graft reactions

A turkey subline at the Ohio Agricultural Research and Development Center was developed by DNA typing of the MHC using a chicken MHC Class II probe, and it segregated for specific MHC genotypes. Histocompatibility was examined between turkeys of known MHC genotype using skin graft procedures, mixed lymphocyte reactions (MLR), and graft-versus-host reactions (GVHR). Skin grafts were exchanged among 3-wk-old turkeys and it was found that when birds shared DNA patterns (genotypes), the skin grafts were usually accepted. In contrast, skin grafts were always rejected when birds did not share the identical DNA pattern. Similarly, MLR only occurred when the lymphocytes were derived from birds that did not share the same DNA pattern. Lastly, GVHR were examined in embryos injected with either sire or dam blood. The GVHR in embryos was dependent on the parental MHC genotype. Four MHC haplotypes were identified in the turkey subline. The turkey MHC has been designated MhcMega-B, and each of the haplotypes, Mega-B(1) through Mega-B(4).

The Turkey Major Histocompatibility Complex: Identification of Class II Genotypes by Restriction Fragment Length Polymorphism Analysis of Deoxyribonucleic Acid

Using a chicken Class II MHC clone in Northern blot analysis, tissue-specific expression of turkey Class II MHC genes was observed in the embryonic bursa of Fabricius as well as in the adult spleen. In contrast, there was no detectable expression in the embryonic liver, brain, or spleen. Southern blot analysis of BamHI-digested turkey DNA revealed two restriction fragment length polymorphism (RFLP) patterns that did not deviate significantly from single-gene Mendelian inheritance. Further analysis of PvuII-digested DNA from 325 turkeys showed four distinct RFLP patterns that segregated within the turkey lines studied. Because the chicken Class II MHC clone hybridized specifically to mRNA in immune-associated tissues, and because it identified polymorphisms among turkeys, the chicken clone is suggested to identify four turkey Class II MHC genotypes. The current study provides good evidence that RFLP analysis of DNA can be used as a means for molecular genotyping at the MHC in turkeys.

Interferon induction of chicken MHC class I gene expression: phylogenetic conservation of the interferon-responsive element

The 5' upstream region of a chicken MHC class I gene BF-IV contains sequence motifs similar to the interferon consensus sequences (ICS) contained in promoters of many mammalian interferon-regulated genes. To study a possible functional role of this putative chicken ICS, an oligonucleotide spanning the upstream sequences of the BF-IV gene (-174/-194) was cloned singly or in multiple copies before the herpes TK promoter controlling the chloramphenicol acetyl transferase (CAT) gene (pBLCAT2). Transient expression studies performed with primary chicken fibroblasts (CEF) showed that the chicken ICS represses constitutive promoter activity. The chicken ICS, however, enhanced CAT activity up to 20-fold following treatment with chicken interferon (IFN). Deletion analysis of the BF-IV promoter also confirms that the upstream DNA sequences (-174/-194) contain a functional ICS recognized by chicken interferon. The murine ICS of the H2-Ld gene was also activated by chicken interferon when introduced into CEF. IFN activation of chicken ICS containing reporters was also observed in transformed chicken fibroblast lines. We show that the chicken ICS binds two specific nuclear factors present in chicken fibroblasts which are induced by interferon. These factors were also capable of recognizing the mouse ICS, suggesting the conservation of a relevant DNA-binding protein. Taken together, these data indicate that the chicken ICS motif contained in a sequence from -174 to -194 of the BF-IV gene acts as a strong interferon-response element, which has been functionally conserved during about 270 million years of separate evolution of mammals and birds.

Association of the major histocompatibility complex with avian leukosis virus infection in chickens

1. Association of the B blood group, the major histocompatibility complex (MHC) in chickens, with avian leukosis virus (ALV) infection shown by shedding of group-specific (gs) antigen was studied in an Australorp line selected for short oviposition interval to improve egg production. Three haplotypes (B8a, B9a and B21) were segregating in this line at frequencies of 66.7, 15.6 and 17.8%, respectively, averaged over three generations. 2. The relative risk (odds ratio) of a hen becoming a gs-antigen shedder was calculated for progenies of the dams shedding gs-antigen and those of non-shedding dams separately and pooled over three generations. In the progenies of shedding dams, the relative risk was not significantly different from 1.0 for the three haplotypes. In contrast, in the progenies of non-shedding dams, the relative risk was 0.67, 0.48 and 2.53 for B8a, B9a and B21, respectively, with the last two ratios being significantly different from 1.0. 3. The average effect of haplotype substitution on probability of shedding was estimated from a linear logistic model. The estimates (relative to zero for B8a) for B9a and B21, respectively, were -0.26 and 0.03 among the progenies of shedding dams, and -0.16 and 0.87 among the progenies of non-shedding dams. The last estimate only was highly significant. 4. These results suggest that the three haplotypes were similar in susceptibility to congenital infection through hatching eggs, but differed in susceptibility to post-hatching infection from other infected birds.

Thymic nurse cell lymphocytes react against self major histocompatibility complex

It has been postulated that thymic nurse cells (TNC), lymphoid-epithelial complexes composed of thymocytes enclosed within major histocompatibility complex (MHC) class I+ and class II+ cortical epithelial cells, may provide an optimal microenvironment for the process of T cell selection. By transplanting single TNC in the avian chorionallantoic membrane assay we demonstrate that a significant portion of intra-TNC lymphocytes (TNC-L) possess reactivity against self-MHC molecules. The frequency of these autoreactive cells among TNC-L exceeds by far that of thymocytes or peripheral blood lymphocytes of the same donor. These results indicate that TNC-L constitute a T cell population enriched for self-MHC reactivity, i.e. cells that have undergone positive selection, but not yet deletion and/or deactivation.

Primary structure and ontogeny of an avian CD3 transcript

The structure of a chicken CD3 chain has been determined by isolating a cDNA clone (T11.15) that encodes a 175-amino-acid-long protein, including the NH2-terminal signal peptide. In Northern blot experiments, the earliest expression of the T11.15 transcript was detected in the thymus at embryonic day 10 (i.e., 1 day after cytoplasmic expression of a CD3 epitope recognized by a specific monoclonal antibody [CT3; Chen, C.L.H., Ager, L.L., Gartland, G.L. & Cooper, M.D. (1986) J. Exp. Med. 164, 375-380], but 2 days before the appearance of clonotypic components of the T-cell antigen receptor). Sequence similarity of this chicken protein sequence compared with that of the known mammalian CD3 gamma and delta polypeptides was 36-39% and 39-40%, respectively. Amino acid sequence alignments between avian and mammalian CD3 revealed maximum conservation in the transmembrane and cytoplasmic domains as well as in the regions flanking the cysteine residues in the extracellular domain, underlining their functional importance. The difficulty of unambiguously assigning this chain to a single mammalian CD3 subunit on the basis of sequence comparison raises the possibility that this polypeptide represents a derivative from an ancestral form of the gamma and delta chains. It is thus possible that a single chain may play the role of both CD3 gamma and delta subunits in the chicken CD3 complex or, alternatively, that gene duplications occurred independently in the avian and mammalian lineages.

Ribosomal and chromosomal protein cDNA clones of Xenopus laevis thymus isolated with differential screening

1. Xenopus laevis is an excellent system for the study of the evolution and ontogeny of the immune system. But since only immunoglobulin genes have been isolated from this species, we undertook to isolate other genes expressed in an immunologically important organ, the thymus. 2. We used differential screening of a thymus cDNA library with cDNA probes made from thymus and from erythroblasts. 3. Approximately 50 clones which hybridized to the probe from thymus, but not from erythroblast, were isolated and sequenced from their termini. 4. Several clones were identified in data bank searches by their similarity to previously published sequences, and the partial sequences of these loci are reported here. 5. These include elongation factor 2, ribosomal protein S11, ribosomal protein S13, and the high mobility group protein. 6. Although these genes are not expected to be involved in an immune function, the availability of these sequences will facilitate the study of these loci in this species.