MicroRNAs (miRs) have emerged as useful biomarkers for different disease states, including
allergic inflammatory diseases such as asthma and eosinophilic esophagitis (EoE). Serum miRs are
a possible non-invasive method for diagnosis of such diseases. We focused on microRNA-21 (miR-21)
levels in serum, in order to assess the feasibility of using this gene as a non-invasive biomarker for
these diseases in the clinic, as well as to better understand the expression pattern of miR-21 in allergic
inflammation. We used quantitative PCR (QPCR) to assay miR-21 and other control miRs in esophageal biopsies from
EoE patients and serum samples from EoE and asthma patients. Serum levels of miR-21 were significantly elevated in patients
with asthma, whereas serum miR-21 levels were not associated with the presence of allergen-specific IgE (i.e.
atopy). Esophageal biopsies showed a large elevation of miR-21 in EoE and an increase in miR-21 in EoE serum. Control
U6 miR did not vary between asthma and control patients, however EoE serum had significantly decreased U6 microRNA
compared to controls. The decreased U6 in EoE sera did not completely account for the relative increase in miR-21 in the
sera of EoE patients. We report for the first time that miR-21 is elevated in the sera of both asthma and EoE patients. We
find no relation between serum miR-21 levels and atopy. Our results thus suggest miR-21 is a novel biomarker for human
allergic inflammatory diseases.
Keywords: Asthma, allergic inflammation, eosinophilic esophagitis, microRNA, Th2.
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