ADVANCES IN CELIAC DISEASE
Darren Craig; Gerry Robins; Peter D. Howdle
Curr Opin Gastroenterol. 2007;23(2):142-148. ©2007 Lippincott Williams & Wilkins
Posted 02/21/2007, Medscape
Abstract and Introduction
Abstract
Purpose of Review: Increasing numbers of atypical or asymptomatic cases of celiac disease are being
diagnosed. This review aims to summarize recent critical research in celiac disease.
Recent Findings: Alternative candidate genes outside of the human leukocyte antigen complex continue to be
identified, whilst innate and adaptive immune responses to key gliadin epitopes are now both recognized to be
important in celiac disease pathogenesis.
Summary: Serological tests and small bowel biopsy remain the cornerstones of diagnosis. Treatment options
other than the restrictive gluten-free diet remain limited.
Introduction
In this review we focus on recent advances in the understanding of celiac disease prevalence, diagnosis and
pathogenesis and review current and future treatment strategies.[1**]
Prevalence
The prevalence of celiac disease amongst the general population may be as high as 1%.[2**] Whilst mass screening
of the general population is likely to prove impractical, screening of high-risk groups should produce a higher
case yield. Several case-finding studies in patients with type 1 diabetes, using a combination of immunoglobulin
A (IgA) anti-tissue transglutaminase II antibodies (anti-TG2), IgA endomysial antibodies (EMAs) and subsequent
confirmatory duodenal biopsies, found a prevalence of 2.5-8.4%.[3-5] Serological screening alone with anti-TG2 in
a cohort of 967 adult Danish patients with type 1 diabetes found 2% seropositivity.[6] A small study also suggested
that the prevalence of celiac disease is increased amongst patients with inflammatory bowel disease.[7]
The mode of presentation of celiac disease is changing.[8*] A recently published prospective study by the Dutch
Pediatric Surveillance Unit carried out between 1993 and 2000 revealed 1071 new cases aged under 15 years.
Overall crude incidence rate (0.81/1000 live births) was increased compared with a similar study from 1975 to
1990 (0.18/1000 live births), and significantly more children diagnosed over the time period of the current study
had atypical symptoms and subtle histological changes on small bowel biopsy.[9*] This significant negative trend
in presentation with diarrhea was also seen in a retrospective study analyzing celiac disease patients seen in a
single US center over a 52-year period, which showed a highly significant decrease in the proportion of
presentations with diarrhea from 71.4% prior to 1980 to 37.2% after 2000. This negative trend, accompanied by
an increase in atypical presentations with osteopenia and iron-deficiency anemia, was demonstrable even before
the widespread availability of serological testing in the US in the early 1990s.
Primary care doctors are increasingly identifying celiac disease patients, and these cases now form the majority of
new referrals to specialist celiac disease centers.[10] A specialist Italian celiac disease center attempted to raise
awareness amongst primary and secondary care doctors about the atypical manifestations of celiac disease and the
benefits of serological testing in high-risk patient groups, and rapidly increased the proportion of asymptomatic
cases from 8 to 15%.[11*]
1
Screening
The impact of screening large numbers of asymptomatic patients for celiac disease has important resource
implications. In addition, there may be little immediate health benefit for screen-detected, asymptomatic cases
since the main treatment for celiac disease, the gluten-free diet (GFD), leads to dietary restrictions and possible
social difficulties. Whilst previous studies have found poor dietary compliance amongst screen-detected,
asymptomatic patients,[12*] a Finnish study suggested compliance comparable with symptomatic celiac disease
patients could be achieved.[13**] Of the screen-detected patients, 96% were adhering to a strict or fairly-strict
(gluten less than once per month) GFD at a median of 14 years, a rate similar to those patients diagnosed due to
their symptoms. Assessment of dietary compliance with IgA EMA and anti-TG2 testing demonstrated
seronegativity in 49 of the 53 patients. Importantly, dietary compliance was not linked to age at diagnosis, since
concerns about compliance amongst those diagnosed with celiac disease in adolescence compared with adulthood
are well documented.[13**] The SF-36 health questionnaire was used to compare health-related quality of life
between the general Finnish population and the screen-detected celiac disease patients, and on this scale the
screen-detected patients had significantly better mental health scores than the general populace (n = 2060) and
comparable scores for all other aspects of general health. The general applicability of these results worldwide is
limited, since in Finland celiac disease is widely recognized and gluten-free foodstuffs are widely available both
in restaurants and supermarkets.
Celiac disease screening amongst women of reproductive age could yield significant health benefits. A Swedish
cohort study[14**] compared 2078 births by women diagnosed with celiac disease prior to or after the birth of an
infant with the background child-bearing population, and found that having undiagnosed maternal celiac disease
at birth was strongly linked to low or very low infant birth weight, lower placental weights and higher Cesarean
section rate. In contrast, mothers diagnosed with celiac disease more than 4 years prior to giving birth did not
have these markers of adverse fetal outcome when compared with the control population, presumably due to
effective implementation of a GFD. Another UK-based cohort study, however, did not demonstrate this
association.[15]
Cost-effectiveness of Celiac Disease Testing
The most cost-effective means of testing for celiac disease in at-risk or symptomatic patients was analyzed in a
prospective study of 538 Israeli military personnel.[16*] The current regimen for testing within the Israeli military
for suspected celiac disease involves serological testing (guinea-pig anti-TG2, EMA and IgG anti-gliadin
antibody (AGA)) of all personnel, followed by small bowel biopsy if positive. The study patients were classified
as high risk if they had more than one complaint attributable to possible celiac disease or as low risk if they had
only one complaint. The total cost of this protocol was US$154 552 (US$287 per patient), with eight new celiac
disease cases identified, all within the 'high-risk' subgroup. Analysis revealed that EMA testing was the most
sensitive and specific serological test (100% and 99%, respectively), with the utility of guinea-pig anti-TG2
limited by a low positive predictive value. The authors conclude that the most cost-effective testing regimen
involves a two-step protocol of single serological testing (EMA testing) and subsequent duodenal biopsy in highrisk patients, with simple clinical follow-up (without serological or endoscopic testing) of patients with isolated
complaints. They recommend that testing should only be carried out in this latter group if symptoms persist or
progress. Such an approach would cost an estimated US$46 501, saving 70% on the current practice of testing all
those even with one complaint.
Point-of-care Testing
Point-of-care testing (POCT) may be useful in order to aid diagnosis and also to monitor compliance with
treatment. A Finnish and Hungarian group has developed a rapid (30 min) testing kit which is able to qualitatively
identify
TG2/IgA anti-TG2 complexes in hemolyzed blood.[17**] This four-winged stick also provides a positive control for
plasma IgA, thereby identifying patients with IgA deficiency, as well as a negative control. When initially tested
2
retrospectively on 164 stored blood samples of patients undergoing upper gastrointestinal investigations (99 of
whom had celiac disease), the test had a sensitivity of 97% and a specificity of 96.9%. The kit was then tested
successfully using blood from TG2 knockout mice to confirm lack of contamination from other blood proteins
before a prospective trial on 120 patients at high risk for celiac disease. The testing kit identified 39 new celiac
disease cases and had a sensitivity of 97.4% and a specificity of 97.6%. To validate the ability of the testing kit to
monitor compliance, the group tested 254 IgA+ celiac disease patients on a GFD with EMA and anti-TG2
serology as well as the POCT kit, and demonstrated strong concordance with all three testing methods. Dietary
lapses were strongly linked with antibody and POCT positivity, and a positive POCT result enabled delivery of
immediate dietary advice, resulting in a 75% reduction in positive results in these patients upon retesting 3-6
months later. A control group tested solely with EMAs and receiving mailed dietary advice when necessary had
only a 29% reduction in positive results on retesting. The usefulness of this testing kit outside a trial environment
will need to be studied, but the initial results look promising.
Atypical Cases
Whilst the diagnosis of celiac disease can be readily made in patients with symptoms, positive serological tests
and histological evidence of villous atrophy, considerable debate exists surrounding patients with negative
serological tests or equivocal duodenal histology. These patients can come from two groups - 'silent' celiac
disease when the patients are symptom free but bear the hallmarks of the disease on histological grounds, and
'latent' celiac disease when serological tests are positive but there are no or minimal histological changes, such as
increased density of ?d+ intraepithelial lymphocytes (IELs) or CD25+ lamina propria cells.[18*]
Serological testing can be used as an initial diagnostic tool in patients with symptoms or at-risk groups, but the
importance of histological confirmation of celiac disease was confirmed by two trials this year. Salmi et al.[19**]
studied IgA EMA testing in 177 patients with duodenal biopsies demonstrating villous atrophy and crypt
hyperplasia. Twenty-two of these patients (all of whom had normal IgA levels) were found to be IgA EMA
negative. The biopsies of 18 of these patients, along with 17 EMA postive celiac disease patients and 20 nonceliac disease controls, were further analyzed for IgA and TG2 deposits using mouse monoclonal anti-TG2. All
35 celiac disease patients demonstrated small bowel mucosal IgA deposits colocalized with gluten-dependent
TG2 deposition, whereas none of the controls demonstrated this. The intensity of TG2 targeted TG2/IgA anti-TG2
complexes in hemolyzed blood.[17**] This four-winged stick also provides a positive control for plasma IgA,
thereby identifying patients with IgA deficiency, as well as a negative control. When initially tested
retrospectively on 164 stored blood samples of patients undergoing upper gastrointestinal investigations (99 of
whom had celiac disease), the test had a sensitivity of 97% and a specificity of 96.9%. The kit was then tested
successfully using blood from TG2 knockout mice to confirm lack of contamination from other blood proteins
before a prospective trial on 120 patients at high risk for celiac disease. The testing kit identified 39 new celiac
disease cases and had a sensitivity of 97.4% and a specificity of 97.6%. To validate the ability of the testing kit to
monitor compliance, the group tested 254 IgA+ celiac disease patients on a GFD with EMA and anti-TG2
serology as well as the POCT kit, and demonstrated strong concordance with all three testing methods. Dietary
lapses were strongly linked with antibody and POCT positivity, and a positive POCT result enabled delivery of
immediate dietary advice, resulting in a 75% reduction in positive results in these patients upon retesting 3-6
months later. A control group tested solely with EMAs and receiving mailed dietary advice when necessary had
only a 29% reduction in positive results on retesting. The usefulness of this testing kit outside a trial environment
will need to be studied, but the initial results look promising.
Latent Celiac Disease
The implications of positive serological tests along with an apparently normal duodenal biopsy are important in
terms of patient follow-up and treatment, since it is unclear whether these patients benefit from a GFD.[21*] Paparo
et al.[18*] analyzed 24 histologically 'normal' jejunal biopsies from children with positive serum EMA and
compared these biopsies with 100 age-matched celiac disease patients with flat mucosa and 50 control children
with other diagnoses. They demonstrated a significant increase in γd+ and CD3+ IELs, both of which are thought
to be markers of gluten sensitivity, amongst the 'normal' jejunal biopsy group compared with controls. The
3
γd+/CD3+ IEL increases were even greater in the overt celiac disease group, suggesting a spectrum of
inflammatory activity only resulting in overt histological damage in a proportion of cases.
The implications of these minor histological changes were further studied in a pediatric case-control study by a
Finnish group who followed up 76 children with minor villous height changes and increased epithelial IELs on
initial duodenal biopsy between 1976 and 1990. Retesting with serological markers and repeat duodenal biopsy
uncovered only one new case and revealed the poor predictive value of these markers in determining risk of future
celiac disease.[22] Overall, uncertainty remains over the long-term risk of developing clinical disease for patients
with borderline histological changes on biopsy.
IgA deposition did not correlate with the degree of mucosal damage, but did decrease on retesting following a
median of 13 months of GFD, as did clinical symptoms in all 35 patients. Interestingly, the seronegative patient
group differed significantly from those exhibiting positive serum EMA - being significantly older (median of 55
versus 40 years), more likely to be male and having significantly more abdominal symptoms suggestive of severe
disease, such as diarrhea and abdominal pain, at initial testing. It is also noteworthy that three of the seronegative
patients had small bowel lymphoma. The authors suggest that seronegativity may result in cases in which a
prolonged, severe immunological reaction at the intestinal mucosal surface increases antibody avidity, reducing
bloodstream overspill from the intestine. Carroccio et al.[20**] analyzed 191 patients with biopsy proven celiac
disease, with 15% (29 patients) being seronegative for either EMA or anti-TG2. The seronegative patients had
only mild villous atrophy or increased IELs on duodenal biopsy, yet when duodenal biopsy culture medium was
tested with anti-TG2, 24 of these 29 patients tested positive. The sensitivity and specificity of anti-TG2 testing of
culture medium was 98% and 100%, respectively. Both these papers emphasize that whilst serum IgA EMA and
IgA TG2 tests have high specificity, duodenal biopsy remains vital for confirming diagnosis.
Genetics
Expression of the major histocompability complex (MHC) class II human leukocyte antigen (HLA) DQ2
heterodimer in either cis or trans configurations is found in approximately 90% of celiac disease cases, with the
transmembrane HLA-DQ8 heterodimer accounting for a further 5-10% of cases.[23**] Two forms of HLA DQ2
exist - DQ2.5 and DQ2.2 - with DQ2.5, encoded by DQA1*0501 and DQB1*0201, being most strongly linked
with celiac disease. The function of the DQ molecule is to present exogenous peptide antigens, such as
deamidated gluten molecules, to CD4+ helper T cells. Despite the importance of HLA-DQ2 and DQ8 in celiac
disease, they are expressed by some 30% of the normal population, and this, combined with haplotype studies
showing that HLA genes contribute only about 40% of the total genetic predisposition to celiac disease,[24] has led
to the hunt for alternative candidate genes. MHC class 1 genes located on chromosome 6 have previously been
studied in relation to celiac disease with variable results. HLA-G, a class 1b antigen thought to have an
immunomodulatory function, was studied by Torres et al.[25*] who used a monoclonal antibody against HLA-G to
study its expression in duodenal biopsies of 24 children with celiac disease. They demonstrated HLA-G
expression restricted to the inner surface of crypt cells in all the celiac disease patients but in none of the control
group of nine patients.
The CD28/CTLA4/ICOS gene cluster has also been the subject of scrutiny in recent years. The CTLA4 gene is
thought to regulate T-cell immune function and an English group found a common haplotype in this gene through
single nucleotide polymorphism (SNP) tagging of a large Caucasian celiac disease cohort.[26*] Whilst two
individual SNPs showed significant association, the combination of alleles in one particular haplotype showed
strong celiac disease linkage (odds ratio 1.41, P < 0.001). Other linkage studies this year demonstrated a
correlation between mannose binding lectin polymorphisms and celiac disease, although this linkage was
strongest in the very rare DQ2/DQ8 negative subgroup,[27] whilst a Spanish group failed to find an association
between interleukin (IL)-10 haplotypes and celiac disease.[28]
The exact role of poly (ADP-ribose) polymerase-1 (PARP-1) in inflammation is unclear, but a microsatellite in
the promoter region of PARP-1 has been shown to have a significant association with celiac disease in a cohort of
4
120 Spanish children,[24] and the authors suggest that this haplotype could result in low levels of PARP-1
expression and subsequently increased enterocyte apoptosis.
Pathogenesis
Prolamins, namely gliadin from wheat, hordeins from barley and secalins from rye, have been identified as the
trigger for celiac disease. The key characteristic of these peptides is their high glutamine and proline content,
rendering them resistant to much of the activity of intestinal chymotrypsin and pepsin.[29-31]
Toxic Gliadin Peptides
Poorly digested gluten peptides appear to trigger both an innate, early immune response and an adaptive response.
Shan et al.[31] have previously identified an exceptionally immunoreactive, digestion-resistant, 33-mer α-2 gliadin
peptide and they confirmed the importance of this peptide by using deletion mutations to remove it from the α-2
gliadin epitope.[32**] The mutant peptide digestion mixture elicited virtually no response from four polyclonal Tcell lines from celiac disease patients compared with a vigorous response with the wild-type peptide. The group
then attempted to identify further immunodominant peptides. Using recombinant ?-5 gliadin, a 26-mer peptide
was identified that was resistant to proteolysis and was a good TG2 substrate. The group then used computational
proteome analysis of 157 gluten proteins from the National Center for Biotechnology Information (NCBI)
proteomic database to predict residues likely to survive digestion and act as toxic peptides in celiac disease. A
total of 128 such peptides, all with 18 or more amino acids, were identified. Interestingly, the in-silico analysis of
other control proteins, including avenins from oats, predicted that these proteins will break down into fragments
no longer than 10 amino acids long, perhaps explaining their tolerability in celiac disease patients.
Anderson et al.[33] have previously described their use of interferon (IFN)-γ ELISPOT to detect HLA-DQ2
restricted CD4+ T cells in peripheral blood following gluten challenge. They used this technique to identify
amino-acid substitutions in the immunodominant p57-73 epitope which would diminish IFN? responses whilst
retaining IL-10 immunoregulatory activity.[34*] A core sequence of four amino acids at positions 64-67 within this
epitope was identified. Several substitutions, in particular threonine for glutamic acid at p65, resulted in inhibition
of IFN-γ activity whilst retaining the capacity to stimulate IL-10. The next step will be to attempt to modify grains
with these substitutions to produce less toxic wheat varieties.
Intestinal Barrier Disruption
In order for gliadin peptides to activate antigen-presenting cells (APCs), they must cross the intestinal barrier to
the lamina propria. It is suspected that celiac disease patients have compromised epithelial function secondary to
impaired tight junction protein function and increased zonulin release. Sander et al.[35*] used the Caco-2 cellular
model of enterocytes to measure transepithelial resistance (TER) following the addition of gliadin to the luminal
surface, and demonstrated a reversible, 60% reduction in TER by 100 min. This appeared to be due to a selective
increase in paracellular permeability, particularly to molecules of similar size (4 kDa) to gliadin peptides, whereas
100 kDa molecules failed to pass. The discovery of a genetic link between celiac disease and a myosin IXB
variant involved in tight junction assembly and cytoskeleton remodeling further emphasizes the potential
importance of disrupted intestinal barrier function as a primary process in celiac disease pathogenesis. [36*]
Initial Inflammatory Responses
Evidence that IELs may contribute directly to villous atrophy was gained by an in-situ hybridization study of
duodenal biopsies from 11 children with celiac disease which demonstrated an increase in epithelial cells
expressing perforin mRNA, particularly amongst those with florid disease.[37] Gluten challenge led to a further
dose-dependent increase in perforin mRNA expression, suggesting a potential direct effect of gluten upon IEL
stimulation.
5
A dual role for the cytokine IL-15 has recently been suggested.[38**] IL-15 overexpression is known to be
associated with several inflammatory intestinal disorders including celiac disease and is important for IEL
function. This group used enzyme-linked immunosorbent assay (ELISA) of cell culture supernatant to assess IL15, IFN-γ and tumor necrosis factor-a (TNF-a) production in 46 celiac disease patients (25 untreated) and 22
controls. They managed to separate enterocytes from lamina propria cells in order to examine site-specific IL-15
expression and demonstrated significantly higher IL-15 levels in enterocytes of untreated celiac disease patients
compared with either treated patients or the control group. IEL proinflammatory cytokine production, IEL
cytotoxicity towards cocultured Caco-2 cells and proliferation of untreated IELs were all significantly increased in
the untreated celiac disease group compared with treated and control groups after further IL-15 stimulation of
IELs. Treatment with IL-15 reduced apoptosis in both control and untreated IELs in a dose-dependent manner.
Lamina propria mononuclear cells from untreated patients also showed significantly higher IL-15 production
compared with cells from patients on GFD or controls, and were significantly more reactive to stimulation from
lipopolysaccharide or IFN-γ. Since IL-15 is also known to promote dendritic cell and macrophage maturation,
there appears to be a key role for IL-15 in both innate and adaptive immune responses in celiac disease.
Tissue Transglutaminase
The major role of the ubiquitous TG2 is to catalyze the deamidation of key glutamine residues to negatively
charged glutamic acid, improving binding of the peptide with DQ2 restricted APCs. Maiuri et al.[39*] used a
monoclonal antibody (6B9 mAb) against surface TG2 to block its actions. They demonstrated that TG2 is
upregulated by innate gluten peptides but not by already deamidated forms, and then showed that blocking TG2
with 6B9 mAb prevented gliadin fragment induced apoptosis in biopsies from celiac disease patients. 6B9 mAb
also significantly inhibited stimulation of CD3+, CD25+ and CD69+ cells in the lamina propria. The use of 6B9
mAb was highly effective at reducing gliadin-induced infiltration of the epithelium by CD8+ lymphocytes. The
results suggest that in addition to its role in the deamidation of glutamine residues, TG2 influences both the innate
immune response and lymphocyte migration during the adaptive phase. TG2 has been shown to be expressed
preferentially in the basement membrane and lamina propria in active celiac disease compared with control
patients,[40] and this, combined with evidence that TG2 binds deamidated gliadin peptides to interstitial collagen in
the intestinal extracellular matrix,[41*] suggests TG2 may haptenize collagen to gliadin and may start to explain the
association of celiac disease with connective tissue disorders.
Dendritic Cell Maturation
Dendritic cells play a key role in antigen presentation to DQ2 or DQ8-restricted CD4+ T cells. In a study on blood
from healthy donors, dendritic cells, when treated with gliadin digests, were shown to markedly increase their
release of the proinflammatory cytokines IL-6, IL-8 and TNF-α.[42*] Gliadin-treated dendritic cells were able to
stimulate allogenic T cells more effectively than untreated dendritic cells and the stimulation of dendritic cells by
gliadin appeared to involve nuclear factor κB and mitogen-activated protein kinases. It is still unclear how gliadin
epitopes interact with dendritic cells, and the work needs to be extended in celiac disease patients. Statins are
thought to have effects upon immune responses, including T-cell proliferation, and atorvastatin has recently been
shown to increase dendritic cell apoptosis and, at lower doses, to impair maturation of lipopolysaccharidestimulated dendritic cells from seven celiac disease patients on a GFD.[43*] Unfortunately, in this same study, invitro attempts to use atorvastatin to limit production of proinflammatory cytokines IFN-γ, IL-5 and IL-4 from
the biopsy specimens failed to show any benefit.
T-cell Receptor Binding With Presented Peptides
The binding of T cells to gliadin peptides presented by DQ2 restricted APCs has been further investigated in vitro
this year.[44,45] Polyclonal T-cell lines derived from 13 celiac disease patients were used to carry out detailed
mapping of T-cell stimulatory sequences from a and γ-gliadin peptides, and the binding of these epitopes was then
reanalyzed using lysine substitutions at positions 4 and 6. The γ-gliadin epitopes were all less strongly recognized
than the 33-mer α-gliadin epitope but did demonstrate a core region of nine amino acids where glutamate residues
at positions P4 and P6 appear critical. The positioning of proline residues within these residues are more variable,
6
but appear favorable at positions P1, P3, P6 and P8.[44] The P1 residue points towards the T-cell receptor, and
Stepniak et al.[45] further confirmed the importance of proline residues in this position.
Treatment
The cornerstone of treatment for celiac disease remains a GFD, but compliance problems due to palatability,
variations in food labelling and possible cross-contamination of other foodstuffs by gluten are common.[12*]
Attempts to quantitatively reduce the immunogenic burden by developing less 'toxic' cereals are ongoing. SpaenijDekking et al.[46*] analyzed 16 different wheat strains using T-cell clones from celiac disease patients and mAbs
against known stimulatory T-cell sequences in gliadin and glutenin. Whilst all the varieties did contain some
stimulatory epitopes, three grains were identified which demonstrated very low T-cell and IFN-γ stimulation,
suggesting low immunogenicity. This same group has similarly demonstrated that the Ethiopian cereal tef lacks
T-cell stimulatory epitopes.[47] The next challenge will be to attempt commercial production of these less toxic
cereals and to ensure they have similar baking qualities to cereals containing both high molecular weight
glutenins and gliadins.[48,49]
The main toxic celiac disease gluten epitopes appear to be generated by subtotal digestion of prolamins by
pancreatic enzymes. The use of animal enzyme therapy to 'detoxify' gluten could increase the range of a GFD.
Cornell et al.[50] carried out a small randomized, double-blinded trial of an encapsulated peptidase extract on 21
adult celiac disease patients in remission. Symptom scores, in particular for abdominal pain and bloating, were
worse in the placebo arm and reached statistical significance amongst the 12 worst affected patients. There was no
beneficial effect, however, upon anti-TG2 titers or histology from enzyme therapy, and although this may have
been due to the small sample size, it raises doubts about the efficacy of this therapy. Attempts to modify gluten
with bacterial prolyl-endopeptidase (PEP) have previously looked promising, with Shan et al.[31] using PEP to
digest an α-gliadin 33-mer peptide strongly resistant to normal intestinal digestion. Matysiak-Budnik and
colleagues,[51*] however, observed PEP degradation of this same peptide and also a 19-mer peptide known to
stimulate IL-15. Both peptides, however, in particular the 33-mer peptide, required very high, prolonged PEP
exposure to ensure complete degradation. At lower concentrations, the peptides were simply cleaved into smaller
fragments still containing T-cell immunostimulatory sequences. Ex-vivo analysis from duodenal biopsies from
seven patients with active celiac disease using high-performance liquid chromatography demonstrated that PEP
treatment, unless at very high concentrations, still permitted transmucosal residues at positions P4 and P6 appear
critical. The positioning of proline residues within these residues are more variable, but appear favorable at
positions P1, P3, P6 and P8.[44] The P1 residue points towards the T-cell receptor, and Stepniak et al.[45] further
confirmed the importance of proline residues in this position.
Conclusion
The high prevalence of silent celiac disease amongst the general population is becoming increasingly well
recognized, and the use of increasingly accurate serological testing in primary care will help identify these
patients earlier. The pathogenesis of this fascinating disorder is becoming clearer, with genetic, dietary, innate and
adaptive immunological factors all contributing, but effective treatments other than dietary restrictions are still
some way off.
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Abbreviation Notes
anti-TG2 = Anti-tissue Transglutaminase II Antibody; APC = Antigen-presenting Cell;
EMA = Endomysial Antibody; GFD = Gluten-free Diet; HLA = Human Leukocyte Antigen;
IEL = Intraepithelial Lymphocyte; IL = Interleukin; PEP = Prolyl-endopeptidase;
POCT = Point-of-care Testing; TG2 = Tissue Transglutaminase II.
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