Allergic rhinitis
AR also known as hay fever, represents the most common allergic disease
and is characterized by increased circulating IgE levels and/or positive
skin prick test. This is triggered by various environmental allergens
including pollen, molds, house dust mite and animal dander, and results
in a cascade of type 2 immune response in which type 2 cytokine
production and eosinophil numbers are increased . AR manifests in the
upper airways and often coexists with
asthma44. Indeed, an
estimated 10-40% of AR patients suffer from
asthma45. Mucosal
inflammation in AR and asthma shares many features, which has led to the
“united airway concept”46 and the idea that
inflammation in AR can progressively extend to the lower
airways47. Even though
AR and asthma often co-exist, many studies examining AR subjects aimed
to uncover unique AR-specific miRNA signatures (Table 2 ).
Indeed, a subset of circulating miRNAs in plasma, miR-206, -338-3p, -329
and -26a, were found to be differentially expressed in patients with AR,
but not in healthy individuals or those with non-allergic asthma. Random
forest model prediction suggested that a subset of six miRNAs allowed
for high accuracy in distinguishing between these three
groups48.
In nasal biopsies, out-off-season AR patients displayed higher miR-7 and
miRPlus-E1194 expression, whereas let-7, miR-498,-187, -874, -143, -886,
-224, and -767 were decreased compared to non-allergic patients
undergoing inferior turbinate
surgery49,50.
The reduced levels of let-7e were confirmed by an additional study,
which also showed increased levels of miR-155, a miRNA involved in type
2 immune responses (see
above51,52),
miR-205 and miR-498 in nasal biopsies of patients with current AR
symptoms50. miR-498 was
also increased in the nasal mucosa of subjects suffering from perennial
allergy, while miR-18a expression was significantly lower in subjects
with perennial allergy compared to subjects with sensitization to
seasonal allergens48.
The correlation of miRNAs with AR symptom severity (Total Nasal Symptoms
Score) revealed 3 down-regulated (miR-572, -1228-, -483) and 9
up-regulated miRNAs in nasal mucosa (miR-1908, -126, -92a, -125a, 19a,
26a, 106a, -181c, -3177). Of the identified miRNAs, miR-126, -19a and
-26a specifically and sensitively predicted AR disease activity in a
receiver operating characteristic (ROC)
analysis53, thus
suggesting that miRNAs may be potential biomarkers in the prognosis of
AR.