Asthma is a chronic inflammatory disorder of the airways in which many
cells and cellular elements play a role, in particular, mast cells,
eosinophils, T lymphocytes, macrophages, neutrophils and epithelial
cells. In susceptible individuals this inflammation causes recurrent
episodes of wheezing, breathlessness, chest tightness and coughing,
particularly at night or in the early morning. These episodes are
usually associated with widespread but variable airflow obstruction
that is often reversible either spontaneously or with treatment. The
inflammation also causes an increase in existing bronchial
hyperresponsiveness to a variety of stimuli.
Asthma is characterized by spastic contraction of the smooth muscle in
the bronchioles, which causes extremely difficult breathing. Asthma is
about 70 percent is caused by allergic hypersensitivity, especially
sensitivity to plant pollens.
Asthma is a common increasing and relapsing disease that is associated
with genetic and environmental factors such as respiratory viruses and
The pathology of asthma is characterised by various changes in the
airways including mucus plugging, shedding of epithelial cells,
thickening of the basement membrane, engorgement of the vessels, and
angiogenesis, inflammatory cell infiltration, and smooth muscle
hypertrophy and hyperplasia. The pathogenesis of asthma can be broadly
subdivided into inflammatory and remodelling components.
The inflammatory features of asthma consist of a dense inflammatory
infiltrate in which eosinophils, mast cells, and CD41 helper T
lymphocytes predominate. Neutrophilic infiltration also arises during
asthma exacerbations and in the late response to allergen challenge.
Dendritic cells seem to be the key cells for antigen presentation in
asthma. Antigens then cause cross-linking of IgE and as a consequence
mast cells are activated and degranulate. Mast cells are important in
the acute airway responses to allergens and may also contribute to
remodelling in chronic asthma. Interest in the mast cell will probably
increase with the recent report that the presence of mast cells in the
smooth muscle layer in bronchial biopsies helps to differentiate
asthma from eosinophilic bronchitis, suggesting that interactions
between mast cells and smooth muscle are important in asthma
pathogenesis. Such an observation is consistent with results of
studies of sensitised human airway smooth muscle in vitro where the
degree of contraction to antigen is related to the number of mast
A defining characteristic of asthma is the presence of many activated
eosinophils, which are thought to contribute to airway epithelial
damage by release of products such as eosinophil major basic protein.
However, the central role for eosinophils as effector...