20
Dec
2018
F
Cr
Feature Review
Clinical
ALLERGIC
RHINITIS
Closely related to asthma,
hay fever has a clear genetic
aspect. What are the key steps
for diagnosing this condition?
PATHOGENESIS
Allergic rhinitis is a type I hypersensitivity
reaction, closely related in its pathogenesis
to asthma and atopic dermatitis.
Cellular pathogenesis
As in other atopic conditions, the development
of allergic rhinitis begins with initial
sensitisation followed by a subsequent allergen
challenge that produces the typical symptoms
of hay fever.
Sensitisation
Turbulent airflow during nasal inspiration
promotes deposition of particulate matter
(including aeroallergens) in the nasal mucosa,
where it is imbibed by antigen-presenting cells
(such as macrophages, CD1+ dendritic cells
and B lymphocytes).
Antigens are processed and their
fragments are presented with class II major
histocompatibility matrix (MHC II) proteins
to T-helper 2 (TH2) cells. 6
Secretion of interleukins and cell surface
protein interactions promote isotypic
transformation of B lymphocytes and results
in the production of large quantities of
allergen-specific IgE (see figure 1).
This abundant IgE binds high-affinity
receptors on mast cells and basophils that are
concentrated in the nasal lamina propria.
Antigen challenge
Subsequent exposure to an allergen to
which an atopic individual is sensitised
invokes a two-phase immune response
in allergic rhinitis.