Co-adjuvant effects of retinoic acid and IL-15 induce inflammatory immunity to dietary antigens.

Under physiological conditions the gut-associated lymphoid tissues not only prevent the induction of a local inflammatory immune response, but also induce systemic tolerance to fed antigens. A notable exception is coeliac disease, where genetically susceptible individuals expressing human leukocyte antigen (HLA) HLA-DQ2 or HLA-DQ8 molecules develop inflammatory T-cell and antibody responses against dietary gluten, a protein present in wheat. The mechanisms underlying this dysregulated mucosal immune response to a soluble antigen have not been identified. Retinoic acid, a metabolite of vitamin A, has been shown to have a critical role in the induction of intestinal regulatory responses. Here we find in mice that in conjunction with IL-15, a cytokine greatly upregulated in the gut of coeliac disease patients, retinoic acid rapidly activates dendritic cells to induce JNK (also known as MAPK8) phosphorylation and release the proinflammatory cytokines IL-12p70 and IL-23. As a result, in a stressed intestinal environment, retinoic acid acted as an adjuvant that promoted rather than prevented inflammatory cellular and humoral responses to fed antigen. Altogether, these findings reveal an unexpected role for retinoic acid and IL-15 in the abrogation of tolerance to dietary antigens.

Similarities of omega gliadins from Triticum urartu to those encoded on chromosome 1A of hexaploid wheat and evidence for their post-translational processing.

The omega-gliadins encoded on chromosome 1 of the A genome were purified from Triticum aestivum L. (2n=6 x=42, AABBDD) cv. Butte86, nullisomic 1D-tetrasomic 1A of cv. Chinese Spring (CS N1DT1A), and the diploid T. urartu (2n=2 x=14, AA ). Reverse-phase high-performance liquid chromatography combined with sodium dodecyl sulfate-polyacrylamide gel electrophoresis of gliadin extracts from CS nullisomic-tetrasomic (NT) lines confirmed the assignment to chromosome 1A. The purified omega-gliadins were characterized by mass spectrometry and N-terminal sequencing. The 1A-encoded omega-gliadins were smaller than 1B- or 1D-encoded omega-gliadins. The N-terminal amino acid sequences for 1A omega-gliadin mature peptides were nearly identical to those for the T. urartu omega-gliadins and were more similar to 1D omega-gliadin sequences than to sequences for T. monococum omega-gliadins, barley C-hordeins, or rye omega-secalins. They diverged greatly from the N-terminal sequences for the 1B omega-gliadins. The data suggest that T. urartu is the A-genome donor, and that post-translational cleavage by an asparaginyl endoprotease produces those omega-gliadins with N-terminal sequences beginning with KEL.

Characterisation and chromosomal localisation of C-type low-molecular-weight glutenin subunits in the bread wheat cultivar Chinese Spring.

Low-molecular-weight glutenin subunits are classically divided into the B, C and D groups. Most attention has been paid to the characterisation of the B and D groups, whereas C subunits, although represented by a large number of protein components, have not been thoroughly characterised, mainly because they tend to separate with the gliadins in many fractionation procedures. Here we describe a procedure for obtaining a fraction strongly enriched in C subunits that has allowed us to determine the chromosomal location of these subunits in the bread wheat cultivar Chinese Spring. This analysis has shown that these subunits are coded on chromosome groups 1 and 6. Comparison between N-terminal amino acid sequencing of B and C subunits has shown that, whereas the former group includes mainly subunits with typical LMW-GS type sequences (76%), the C subunit group is made up almost completely of subunits with gliadin-like sequences (95%), including the alpha-type. These results indicate that the LMW-GSs are likely to be coded not only by the typical Glu-3 loci, but also by loci tightly linked to, and possibly included within, the Gli-1 and Gli-2 loci.

Characterization of a low-molecular-weight glutenin subunit gene from bread wheat and the corresponding protein that represents a major subunit of the glutenin polymer.

Both high- and low-molecular-weight glutenin subunits (LMW-GS) play the major role in determining the viscoelastic properties of wheat (Triticum aestivum L.) flour. To date there has been no clear correspondence between the amino acid sequences of LMW-GS derived from DNA sequencing and those of actual LMW-GS present in the endosperm. We have characterized a particular LMW-GS from hexaploid bread wheat, a major component of the glutenin polymer, which we call the 42K LMW-GS, and have isolated and sequenced the putative corresponding gene. Extensive amino acid sequences obtained directly for this 42K LMW-GS indicate correspondence between this protein and the putative corresponding gene. This subunit did not show a cysteine (Cys) at position 5, in contrast to what has frequently been reported for nucleotide-based sequences of LMW-GS. This Cys has been replaced by one occurring in the repeated-sequence domain, leaving the total number of Cys residues in the molecule the same as in various other LMW-GS. On the basis of the deduced amino acid sequence and literature-based assignment of disulfide linkages, a computer-generated molecular model of the 42K subunit was constructed.

Mechanisms of assembly of wheat high molecular weight glutenins inferred from expression of wild-type and mutant subunits in transgenic tobacco.

Following sequestration into the endoplasmic reticulum, wheat high molecular weight glutenin subunits (HMW-GS) assemble into polymers through intermolecular disulfide bond formation. These polymers, which also include low molecular weight glutenin subunits (LMW-GS), have a broad distribution of molecular mass reaching up to several million daltons. To study the mechanism of assembly of the HMW-GS, we have expressed x- and y-type HMW-GS in transgenic tobacco plants. Both types, when expressed individually or in combination, were incorporated into polymers. Partial reduction of polymers formed by different subunits resulted in different patterns of release of homodimers, heterodimers, and monomers. This suggested different arrangements of intermolecular disulfide bonds or different peptide conformations in the vicinity of the disulfide bonds linking x-x, y-y, and x-y type HMW-GS. A mutant of the x-type subunit, lacking a conserved cysteine in the C-terminal domain, assembled into oligomers linked by intermolecular disulfide bonds, but not into large polymers. This mutant was deposited, however, in dense protein bodies, similar to those formed by the native HMW-GS, suggesting that polymer formation and packaging into protein bodies may be the result of different types of interactions. Pulse-chase labeling of proteins in wheat endosperm showed that the assembly of the HMW-GS into insoluble polymers occurs by a slow process which apparently continues after the initiation of protein body formation.

Intermolecular disulfide bonds link specific high-molecular-weight glutenin subunits in wheat endosperm.

A detergent wash extracted soluble proteins from wheat flour, leaving a residue enriched with insoluble glutenin aggregates. Digestion of this residue with endoproteinase Lys-C, which showed a limited specificity for glutenin subunits, produced several peptides with apparent molecular weights close to those of intact high-molecular-weight glutenin subunits. N-terminal sequencing indicated that the isolated peptides were composed of high-molecular-weight glutenin subunit fragments joined by an intermolecular disulfide bond. In two of these peptides, only two components were found, one from an x-type subunit and the other from a y-type subunit. The isolated peptides all contained at least one x-type C-terminal region and one y-type N-terminal region, suggesting a specific orientation to the intermolecular disulfide linkage.

Use of recombinant inbred lines of wheat for study of associations of high-molecular-weight glutenin subunit alleles to quantitative traits : 2. Milling and bread-baking qualitiy.

Recombinant inbred lines (RILs) derived by single plant descent to F8 from a hybrid of Anza, a low-quality cultivar, and Cajeme 71, a high-quality cultivar, differed in alleles at three high-molecular-weight glutenin (HMW-glu) seed storage protein loci. The 48 RILs were classified by SDS-PAGE for the Anza alleles Glu-Alc (null), Glu-B1b (subunits 7 + 8), and Glu-D1a (subunits 2 + 12) and for Cajeme 71 alleles Glu-A1a (sub-unit 1), Glu-B1I (subunits 17 + 18), and Glu-D1d (subunits 5 + 10). All RILs and parents were grown in a replicated field trial with three levels of nitrogen (N) fertilization. Additive and additive x additive gene effects for the three loci were detected by orthogonal comparisons of means for each of six wheat end-use quality traits. Each HMW-glu genotype was represented by three to ten RILs so that variability among RILs within each HMW-glu genotype could be examined. N effects were consistently small. All traits except flour yield were highly correlated with predictor traits studied earlier. Flour protein content, baking water absorption, dough mixing time, bread loaf volume, and bread loaf crumb score were all correlated, suggesting similar gene control for these traits; however, specific additive locus contributions were evident: αB for flour yield; αB and αD for flour protein; and αB for absorption, but differing in sign; all three loci for mixing time, but αB was negative; and all three loci were positively associated with loaf volume. Digenic epistatic effects were significant for flour yield (αAD), flour protein (αAB), and absorption and mixing time (αAD, αBD). Only flour yield showed a trigenic epistatic effect. Six of seven epistatic effects were negative, thus showing how progress in breeding for high quality may be impeded by interaction of genes which, by themselves, have strong positive additive effects. Considerable genetic variance among RILs within a HMW-glu genotype was detected for all traits, and the summation of α effects accounted for a mean of 13% of the parental differences for the six traits examined in this study. Clearly, further resolution of the genetics of wheat quality would be desirable from a plant breeding point of view.

Use of recombinant inbred lines of wheat for study of associations of high-molecular-weight glutenin subunit alleles to quantitative traits : 1. Grain yield and quality prediction tests.

The high-molecular-weight glutenin subunits (HMW glutenin), encoded by alleles at homoeologous lociGlu-A1,Glu-B1, andGlu-D1 on the long arms of chromosomes1A,1B, and1D of a set of F8 random recombinant inbred lines (RIL) derived from the bread wheat cross Anza × Cajeme 71, were classified by SDS-PAGE. Anza has poor breadmaking quality and HMW-glutenin subunits (Payne numbers) null (Glu-A1c), 7+8 (Glu-B1b), and 2+12 (Glu-D1a); Cajeme 71 has good quality and 1 (Glu-A1a), 17+18 (Glu-B1i), and 5+10 (Glu-D1d). The combinations of these alleles in the RIL were examined for associations with grain yield and four indicators of grain quality - protein content, yellowberry, pearling index, and SDS sedimentation volume. Data were obtained from a field experiment with three nitrogen fertilization treatments on 48 RIL and the parents. Orthogonal partitioning of the genetic variance associated with the three HMW glutenin subunit loci into additive and epistatic (digenic and trigenic) effects showed strong associations of these loci with grain yield and the indicators of quality; however, the associations accounted for no more than 25% of the differences between the parents. Genetic variance was detected among the RIL, which had the same HMW glutenin genotype for all traits. Epistatic effects were absent for grain yield and yellowberry, but were substantial for grain protein content, pearling index, and SDS sedimentation volume. All three loci had large single-locus additive effects for grain yield, protein, and SDS sedimentation volume. Yellowberry was largely influenced byGlu-B1 andGlu-D1, whereas pearling index was associated withGlu-A1 andGlu-B1. Even though the observed associations-of effects of HMW glutenin loci with the quantitative characters were small relative to the total genetic variability, they are of considerable importance in understanding the genetics of wheat quality, and are useful in the development of new wheat varieties with specific desired characteristics.

Molecular cloning of the barley seed protein CMd: a variant member of the alpha-amylase/trypsin inhibitor family of cereals.

The nucleotide and deduced amino-acid sequences of a cDNA clone encoding the barley seed protein CMd are described. The sequence is homologous with those of a family of inhibitors of alpha-amylase and trypsin, except for two short insertions. The longest of these (14 residues) is at the junction between the three proposed ancestral regions that comprise this family of proteins, and has limited identity with alpha-amylases of bacterial origin.

In vitro (organ culture) studies of the toxicity of specific A-gliadin peptides in celiac disease.

Specific peptides of known amino acid sequence were prepared from alpha-gliadin (A-gliadin) by cleavage of the protein with cyanogen bromide and chymotrypsin and purification of the resulting peptides. The three peptides derived from the cyanogen bromide cleavage spanned the complete sequence of A-gliadin (266 residues). Four peptides derived from chymotryptic digestion covered the N-terminal sequence through residue 68. These peptides were tested for toxicity in celiac disease by organ culture of biopsied small intestinal tissues taken from patients with active celiac disease. Enterocyte height was used as a measure of peptide effect on cultured tissues. Five of seven peptides tested significantly inhibited increase of enterocyte height in the cultures and were considered toxic on this basis. The largest common sequences among the toxic peptides were -pro-ser-gln-gln- and -gln-gln-gln-pro-; these sequences were absent from the nontoxic peptides. The relationship of these sequences to the damaging effect of gliadins on the small intestinal mucosa in celiac disease remains to be investigated.

Evidence for the role of a human intestinal adenovirus in the pathogenesis of coeliac disease.

We previously noted a region of amino acid sequence homology between A-gliadin, a major alpha-gliadin component known to activate coeliac disease, and the early region E1b protein of human adenovirus serotype 12 (Ad12), an adenovirus isolated from the human intestinal tract. In the present study sera from coeliac disease patients from the United Kingdom and the United States were assayed for neutralising antibody to Ad12 as evidence of past exposure to that virus and for antibody to synthetic peptides of A-gliadin from the region of shared sequence with the Ad12 E1b protein. Eighty nine per cent of untreated coeliac disease patients had evidence of previous Ad12 infection. There was also a significant increase in the prevalence of neutralising antibody to Ad12 among treated adults (33.3%) and children (30.8%) with coeliac disease compared with controls (0-12.8%) in the western USA and in London. There was no evidence for an increased prevalence of infection with a closely related adenovirus, adenovirus 18, or another enteric virus, Echovirus 11, among coeliac disease subjects. Additional studies documented that a region of A-gliadin that shares amino acid sequence homology with the adenovirus 12 E1b protein could be recognised as an antigenic determinant in active coeliac disease patients. Taken together, these data are compatible with the hypothesis that a viral protein may play a role in the pathogenesis of coeliac disease, perhaps by virtue of immunological cross reactivity between antigenic determinants shared by the viral protein and alpha-gliadins.

Null alleles for gliadin blocks in bread and durum wheat cultivars.

Wheat gliadin proteins are coded by clusters of genes (complex loci) located on the short arms of chromosomes of homoeologous groups 1 and 6 in bread (6x) and durum (4x) wheats. The proteins expressed by the various complex loci have been designated gliadin blocks. In a survey of accessions from the Germplasm Institute (C.N.R., Bari, Italy) collection, several different accessions have been found that lack particular blocks of proteins (null alleles). In some bread wheat accessions, seeds do not express gliadins that are coded by chromosomes 1D and 6A in normal cultivars. Similarly, some durum wheat accessions lack ω-gliadin components coded for by genes on chromosomes 1A and 1B. The missing proteins do not result from the absence of whole chromosomes, but may be the consequence of partial deletion of these genes at a complex locus or result from their silencing.

In vitro activation of adenylate cyclase of atrophic celiac intestinal mucosa by wheat gliadin-derived peptides.

In order to demonstrate that gliadin peptides may interact with cell membranes of celiac small intestinal mucosa, the capacity of these peptides to activate the cell membrane enzyme adenylate cyclase was tested. The addition of peptides from bread wheat purified A-gliadin and whole gliadin (proteins that are toxic for celiac patients) enhanced the adenylate cyclase activity of crude cell membrane preparations obtained from atrophic small intestinal mucosa of celiac patients. No activation of adenylate cyclase of this tissue was observed with peptides from proteins nontoxic for celiac patients (bread wheat albumin and maize prolamin). Gliadin peptides did not activate adenylate cyclase of morphologically normal small intestinal mucosa from normal subjects or from celiac patients in remission. These results, therefore, suggest that peptides from bread wheat gliadin may interact with cell membrane of atrophic small intestinal mucosa of celiac patients.

Specificity of antigliadin antibody in celiac disease.

Celiac disease is activated in genetically susceptible individuals by the dietary ingestion of wheat gluten and similar proteins in other grains. Gliadins are a complex mixture of proteins that contain at least 40 different components in a single variety of wheat. We have purified the four major electrophoretic fractions of wheat gliadin and examined the specificity of antigliadin antibody for those fractions by radioimmunoassay in 30 patients with celiac disease and 30 matched controls. All patients had been on a gluten-free diet for more than 18 mo and were clinically asymptomatic at the time of study. Seventeen of 30 patients had increased antibody levels to one or more of the gliadin fractions. Twelve of 17 patients had elevated antibody to A or 6D alpha-gliadin, 9 of 17 to beta-gliadin, 10 of 17 to gamma-gliadin, and 8 of 17 to omega-gliadin. Of the 17 subjects, 5 had increased antigliadin antibody levels to one gliadin fraction only, whereas 12 had increased levels to two or more fractions. Of the 17 patients with increased antibody titers, 16 had the G2m(n) immunoglobulin heavy chain allotype marker and 14 had the serologic HLA specificities-B8 or-DR3, or both. Definition of the wheat gliadin fractions and specific gliadin peptides that can activate celiac disease remains an open question. These data indicate that antigliadin antibody in the serum of asymptomatic patients with celiac disease who are maintained on a gluten-free diet can be directed against one or a multiple of gliadin fractions.

Possible role for a human adenovirus in the pathogenesis of celiac disease.

Celiac disease in humans is activated by the dietary ingestion of wheat, rye, triticale, barley, and possibly oats. Gliadins in wheat and similar proteins in the other grains are known to activate disease in susceptible individuals. There is a striking association between celiac disease and HLA-B8, -DR3 and/or -DR7, and -DC3. Nonetheless, less than 0.2% of individuals with those serologic HLA specificities develop celiac disease and disease is not always concordant among monozygotic twins. We propose that additional environmental factors may be important in the pathogenesis of celiac disease. To investigate that possibility, we examined a data bank of protein sequences for other proteins that might share amino acid sequence homologies with A-gliadin, an alpha-gliadin component known to activate celiac disease and whose complete primary amino acid sequence is known. These studies demonstrate that A-gliadin shares a region of amino acid sequence homology with the 54-kD E1b protein of human adenovirus type 12 (Ad12), an adenovirus usually isolated from the intestinal tract. The region spans 12 amino acid residues, includes 8 residue identities and an identical pentapeptide, and is hydrophilic in both proteins. Antibody reactive with the 54-kD Ad12 E1b protein cross-reacts with A-gliadin, a 119 amino acid cyanogen bromide peptide of A-gliadin that spans the region of homology and a synthetic heptapeptide of A-gliadin from within the region of homology. We suggest that an encounter of the immune system with antigenic determinants produced during intestinal viral infection may be important in the pathogenesis of celiac disease.

Nucleic acid (cDNA) and amino acid sequences of alpha-type gliadins from wheat (Triticum aestivum).

The complete amino acid sequence for an alpha-type gliadin protein of wheat (Triticum aestivum Linnaeus) endosperm has been derived from a cloned cDNA sequence. An additional cDNA clone that corresponds to about 75% of a similar alpha-type gliadin has been sequenced and shows some important differences. About 97% of the composite sequence of A-gliadin (an alpha-type gliadin fraction) has also been obtained by direct amino acid sequencing. This sequence shows a high degree of similarity with amino acid sequences derived from both cDNA clones and is virtually identical to one of them. On the basis of sequence information, after loss of the signal sequence, the mature alpha-type gliadins may be divided into five different domains, two of which may have evolved from an ancestral gliadin gene, whereas the remaining three contain repeating sequences that may have developed independently.

Chromosomal assignment of genes coding for the wheat gliadin protein components of the cultivars 'Cheyenne' and 'Chinese Spring' by two-dimensional (two-pH) electrophoresis.

The gliadin proteins of the hexaploid bread wheat cultivar 'Cheyenne' (Triticum aestivum L. var. aestivum), which has good mixing and baking characteristics, were analyzed by 2-dimensional (2-pH) polyacrylamide gel electrophoresis (pH 3.2 in the 1st dimension, pH 9.2 in the 2nd). Genes for most of the 35 resolved components were assigned to the chromosomes of homoeologous groups 1 and 6 through the use of various aneuploids and substitution lines. A similar analysis was carried out for the cultivar 'Chinese Spring', which does not have good quality, and which had been analyzed by a different 2-dimensional procedure by Wrigley and Shepherd (Ann NY Acad Sci 209:154, 1973). A coordinate system was devised for description of the components in the 2-dimensional patterns.

Celiac sprue: correlation with murine T cell responses to wheat gliadin components.

Celiac sprue is a disease in humans that is characterized by small intestinal mucosal injury and malabsorption. Dietary exposure to gliadin and similar proteins in rye and barley activates the disease in susceptible individuals. Celiac sprue appears to be the only disease with a marked HLA-association in which the proteins that activate the disease currently are well known. However, bread wheat gliadins are a complex mixture of proteins that contain at least 40 different components. In the present study we have purified the major gliadin components of Scout 66 wheat and used these proteins to examine murine T cell proliferative responses to gliadin. Differences in T cell proliferation stimulated by alpha-, beta-, gamma-, and omega-gliadins paralleled the known structural differences among these proteins. After priming with whole gliadin, the components that stimulated T cell proliferation were the same as those recognized to activate celiac sprue in humans. Studies with reduced and alkylated A-gliadin (i.e., S-methyl A-gliadin) suggested that epitopes determined by the native conformation of A-gliadin may be important in its interaction with T cells. By using three different A-gliadin peptides that span the entire molecule, T cell proliferative responses were shown to be stimulated predominantly by antigenic determinants on the NH2-terminal peptide.