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Tissue Transglutaminase,
Endomysial Antibodies, and
Celiac Disease
David Lucas, M.D.
CP Conference, January 18, 2008
Celiac Disease
Celiac disease is characterized by small intestinal
damage with loss of absorptive villi and
hyperplasia of crypts typically leading to
malabsorption
 Associated with nutrient deficiencies and
increased risk of malignancy (especially
intestinal T-cell lymphoma) with chronic disease
 Precipitated by ingestion of the protein gliadin
(component of wheat gluten) and resolves with
withdrawal of protein
 Gliadin initiates mucosal damage via an
immunological process in individuals with a
genetic predisposition

Celiac Disease
Mechanism responsible for damage is still under
debate
 Small intestinal biopsy is “gold standard” and
reveals flattened/blunted villi
 IgA antibodies against gliadin and endomysium
(a smooth muscle connective tissue) have been
the sole serological test used for both diagnosis
and therapy control
 IgA antibodies to endomysium are very specific
indicators of celiac disease, suggesting one or
more target autoantigens

Tissue Transglutaminase Identification
In 1997, tissue transglutaminase (tTG) as the
unknown endomysial autoantigen was identified
 tTG – otherwise known as erythrocyte, cellular,
endothelial, cytoplasmic, Type II, or liver TG
 Family of calcium-dependent enzymes that
catalyze the crosslinking of proteins resulting in
the formation of epsilon-lysine bonds
 Normally localized within the cytoplasm and
released during wound healing, where it
interacts with cell surfaces or certain
extracellular matrix molecules

Tissue Transglutaminase Identification
tTG can also crosslink with fibronectin,
osteonectin, collagen II, V, and XI,
procollagen III, and nidogen
 Thought to stabilize the provisional
extracellular matrix in granulation tissue
 Also enhanced during apoptosis leading to
irreversible crosslinking of intercellular
proteins
 Gliadin proved to be an excellent substrate
for tTG

Tissue Transglutaminase Identification
Indirect immunofluorescence performed
with high titer Celiac disease serum placed
on monkey esophagus with or without tTG
pretreatment
 Untreated serum revealed a characteristic
endomysial immunofluorescence pattern
consistent with disease whereas the
treated serum pattern nearly completely
abolished endomysial immunofluorescence

Tissue Transglutaminase Identification
This demonstrated that tTG was the
predominant, if not sole, endomysial
autoantigen
 An ELISA for the detection of IgA anti-tTG
was established

Pathogenesis
Fundamental disorder is sensitivity to gluten,
which is the alcohol-soluble, water-insoluble
protein component (gliadin) of wheat and
closely related grains (oat, barley, and rye)
 T-cell mediated chronic inflammatory reaction
with autoimmune component
 Most likely develops as a consequence of a loss
of tolerance to gluten
 Interplay between genetic predisposing factors,
the host immune response, and environmental
factors is central to disease pathogenesis

Pathogenesis
When exposed to gluten, the small intestine
accumulates intraepithelial CD8+ T cells and
large numbers of lamina propria CD4+ T cells,
which are sensitized to gliadin
 Also major histocompatibility complex class II
HLA-DQ2 or HLA-DQ8 haplotype
 Recognition of these peptides by CD4+ T cells
leads to secretion of interferon γ, which
damages the intestinal wall
 Epithelial cells secrete large amounts of IL-15
that activates CD8+ T cells and increases the
risk of lymphoma development.

Thoughts regarding EMA and tTG
EMA is nearly 100% specific and is the gold
standard in serologic testing for celiac disease
 The ease of the assay for anti-tTG (ELISA) as
opposed to EMA (immunofluorescence) has
influenced many reference labs
 In celiac disease, there are EMA and anti-tTG
negative patients, as well as lack of concordance
between anti-tTG and EMA in up to one-third of
patients
 A celiac panel for celiac disease should include
both EMA and anti-tTG serology

Thoughts regarding EMA and tTG
IgA EMA using human umbilical cord had a
sensitivity of 90% and a specificity of 99%
 ELISA anti-tTG antibodies using guinea pig liver
tTG has shown a sensitivity of 93% and
specificity of 95%
 The introduction of human recombinant tTG has
shown to enhance the sensitivity of the anti-tTG
test
 A combination of antibodies should be used – to
include anti-tTG and EMA antibodies, with at
least one being IgG based (IgA deficient
patients)

Additional Points

2.6% of patients with celiac disease have
selective IgA deficiency
– Should have both IgA and IgG base
serological screening tests and total IgA if the
above is suspected

Two further subgroups:
– Patients with only IgG-type antibodies to both
tTG and EMA, but with normal IgA
– Patients with anti-tTG and anti-R1 reticulin
antibodies, but lacking typical EMA
References
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Dieterich W, Ehnis T, Bauer M, Donner P, Volta U,
Riecken EO, Schuppan D. Identification of tissue
transglutaminase as the autoantigen of celiac disease.
Nat Med 1997;3:797–801
Dickey W, Hughes DF, McMillan SA. Reliance on serum
endomysial antibody testing underestimates the true
prevalence of coeliac disease by one fifth. Scand J
Gastroenterol 2000;35:181–183
Stern M. Comparative evaluation of serologic tests for
celiac disease: a European initiative toward
standardization. J Pediatr Gastroenterol Nutr
2000;31:513–519