Introduction
Asthma is a chronic airway disease characterized by bronchial
inflammation, airway hyperreactivity, and reversible airflow limitation;
it is often caused by inhalation of
allergens[1].Pollens
are important outdoor allergens associated with allergic asthma and
seasonal rhinitis[2].Humulus scandens(H.scandens ,
also known as Humulus japonicas or Lücao in Chinese) is a
widespread weed in East Asia[3].In
Korea, Humulus pollen constitutes approximately 18% of total
pollen during the pollination
period[4]. In China, Jia
et
al. first discovered that Humulus pollen is an important allergen
in summer and autumn, second only to Artemisiapollen[5].Among individuals with fall
hay fever, 59% were positive for H.scandens -specific serum
IgE[6]. The symptoms of asthma
triggered by H.scandenspollen are reportedly more serious than those induced byArtemisia pollen, although the mechanism underlying this effect
has not been elucidated[7].
Subcutaneous immunotherapy(SCIT) with
crudeH. scandens pollen extract
(HSE) has been used in China for
many years; this type of therapy can effectively reduce the symptom
scores and medication scores of patients with rhinitis and
asthma[8].However,
the mechanisms underlying immunotherapy with HSE have remained unclear,
thereby limiting the applications of this treatment method. Thus far,
most patients with allergic asthma induced byH.scandenspollen are treated with inhaled and oral corticosteroids, despite the
considerable side effects associated with long-term use of
corticosteroids[9]. Therefore, it is
necessary to establish an animal model of asthma with HSE and to study
the mechanisms underlying successful SCIT.
Murine models of allergic asthma
induced by Humulus pollen were previously established by Ya-li et
al.[10] and Kong et
al.[11]through intraperitoneal (IP)
injection and nasal drip
stimulation. We originally planned to study the mechanisms underlying
immunotherapy with HSE by using this model. However, A fair
number of mice died after two
nasal drops. We repeated the experiment more than three times with
different anesthesia methods that used for nasal drip stimulation,
including IP injection with 1% pentobarbital, inhalation of ether, and
inhalation of isoflurane. Our results were similar, in that most mice
died. The lung histopathology of surviving mice showed acute lung injury
(see Supplementary Material for representative experimental results). We
speculated that these results may be attributed to direct stimulation of
lung tissues with high concentrations of HSE during nasal drip
challenge. Whether this is related to the fact that H.scandens is
a kind of Chinese herbal medicine with heat-clearing and detoxifying
effects[12] is unclear. Therefore, we
attempted to use atomized inhalation for challenge, which is considered
to be milder and has a lower fatality
rate[13]. In addition, IP injection
is the most commonly used sensitization route, but some studies have
suggested that sensitization by subcutaneous (SC) injection is more
effective for eliciting high IgE levels and Th2 cytokines and for
inducing allergic airway
inflammation[14]. For instance,
Conejero et al.[15] established a
murine model of olive pollen allergic asthma through SC sensitization.
In the present study, we compared the IP and SC sensitization routes,
with respective reference to previously established sensitization
methods and allergen dosing[10,
15], to develop an optimized model of
allergic asthma induced by HSE that can better simulate the
immunological and pathological features of human allergic
asthma[16].
Using our asthma model, we then developed a model of rapid SCIT to
simulate the process of clinical SCIT and explore the mechanisms ofHumulus immunotherapy.