To the Editor
In allergic diseases, not only ‘allergic inflammation’, but also
‘epithelial barrier impairment’ play important roles in their
development1. Allergen penetration through epithelium
to the body is essential for allergen sensitizations, which are the most
critical risk factors for the development of allergic diseases. In
children with atopic dermatitis (AD), in which epithelial barrier
impairment is one of its famous features, the prevalences of allergen
sensitization and food allergy (FA) are known to be very
high1. Concerning about the assessment of epithelial
barrier function, while transepidermal water loss (TEWL) is a clinically
useful marker in AD skin, it is quite difficult to evaluate barrier
function in gastrointestinal tracts.
Zonulin (pre-haptoglobin 2), an epithelial tight-junction regulator,
plays an important role in the regulation of epithelial barrier
function2,3.
Recently, zonulin was reported to play a pathogenic role in celiac
disease and other chronic inflammatory diseases23. Sturgeon et al
reported that zonulin transgenic mice, as a result of zonulin-dependent
small intestinal barier impairment and altered gut permeability,
increased morbidity and mortality in the DSS colitis model4.
Because allergen sensitization and chronic inflammation are important in
the pathogenesis of allergic diseases, zonulin has potential to play
significant roles in allergic diseases. However, there are few reports
about zonulin levels in pediatric allergic patients. So, the objectives
of this study are to assess whether i) serum zonulin levels in allergic
children are higher than those in children without allergic diseases and
ii) serum zonulin levels are different among allergic diseases.
To evaluate them, we measured serum zonulin levels in infants and
school-age children (with or without allergic diseases) using zonulin
enzyme-linked immunosorbent assay kit. All infants (9 months old) were
selected from Katsushika cohort study5. Allergic
infants (‘AD infants’) were defined as infants who had doctor-diagnosed
AD, and whose total IgE levels were above normal levels and Eczema area
and severity index (EASI) were above zero. ‘Healthy infants’ were
defined as infants who did not have AD, FA, bronchial asthma (BA), nor
allergic rhinitis (AR), and whose serum total IgE levels were below
measureable limits and EASI were zero. There were significant
differences in total IgE levels and EASI score between groups (AD
infants vs. healthy infants) (Table S1). Allergic school-age children
were recruited in our outpatient clinic in Chiba University hospital and
were defined as children who had doctor-diagnosed FA or BA or both, and
whose total IgE levels were above normal levels. ‘healthy school-age
children’ 6 were defined
as school-age children who did not have AD, FA, nor BA and their serum
total IgE levels were below measureable limits. The details of study
subjects are shown in online supplementary methods and table S1-S3.
Our first question was whether or not serum zonulin levels in allergic
children are higher than those in children without allergic diseases. In
infants, median zonulin levels in AD infants and healthy infants were
28.1 ng/ml (interquartile range (IQR): 23.8-32.3) and 15.3 ng/ml (IQR:
10.0-23.7), so serum zonulin levels were significantly higher in
allergic infants than those in healthy infants (p<0.01)
(Figure 1). To confirm this result in other age group, we evaluated
zonulin levels in school-age children. Same as in infants, serum zonulin
levels in school-age children were significantly higher in allergic
children with FA and BA than those in healthy children without FA, BA,
nor AD (Median (IQR): 29.5 ng/ml (22.6-41.9) and 10.6 ng/ml (9.4-12.2),
p<0.001) (Figure 2a). Those results suggest that zonulin
levels are higher in allergic children than in non-allergic children,
regardless of their age.
To assess our second question, we compared serum zonulin levels in BA
patients with those in FA patients. In this analysis, we selected
asthmatic patients as children who had BA but not FA, and FA patients as
children who had FA but not BA, and there were no significant
differences in total IgE and age between groups (Table S3). Serum
zonulin in FA patients was significantly higher than those in BA
patients (Median (IQR): 38.5 ng/ml (35.0-46.7) and 31.0 ng/ml
(13.6-34.0), p<0.05) (Figure 2b). Those results suggest that
zonulin levels are higher in FA patients than those in BA patients.
Sheen et al reported that Serum zonulin levels were elevated in children
with AD7, and this result was confirmed in our present
paper. On the other hand, zonulin primarily reflects epithelial
permeability in the gastrointestinal tract, it is important to examine
Zonulin levels in other age groups and in patients with other allergic
diseases. As we showed in this paper, in school-age children, zonulin
levels are higher in allergic children than in healthy children, and
higher in food allergy children than in asthmatic children. In general,
many AD infants also have FA and intestinal permeability is repoted to
be increased in younger children with AD but not in older children with
AD 8. Those facts might
influence the serum zonulin levels in infants with AD.
Zonulin regulates intestinal barrier function through the regulation of
tight junctional 2. This
suggests that zonulin may affect allergen permeability in epithelia of
the intestinal tract. Zonulin may contribute to the development of
allergic diseases through allergen sensitization and affect the
appearance of allergic symptoms via their effect on allergen exposure.
There were several limitations in this study. First, the number of study
subjects was small. And secondly, we did not compare zonulin levels in
allergic children to those in children with other non-allergic diseases.
So it is not clear whether serum zonulin is an “allergic marker”, and
zonulin plays a role in the “development” of allergic diseases.
In conclusion, serum zonulin levels are significantly higher in allergic
children than in healthy children. In addition, those levels are
significantly higher in food allergy patients than in asthmatic
patients. Based on the knowledge about the role of zonulin in the
intestinal epithelial barrier regulation, zonulin may play a role in the
development of allergic diseases, especially in FA.