Toxicology of Industrial Compounds

Table 10.1 Chemicals identified as human respiratory allergens
I.KIMBER 139
inhalation of the chemical allergen, it is likely that this is an important
route of exposure in the occupational setting.
It is well established that respiratory sensitization caused by protein
aeroallergens is effected by IgE antibody. This class of antibody in man is
homocytotropic and is able to associate, via specific membrane receptors,
with mast cells, including mast cells in the respiratory tract. Following
subsequent exposure of the sensitized individual to the same allergen, mast
cell-bound IgE is cross-linked and this, in turn, results in mast cell
degranulation and the release of both preformed and newly-synthesized
mediators which provoke acute inflammatory reactions. In the case of
sensitization of the respiratory tract caused by chemicals, however, an
invariable association with the presence of specific IgE antibody has failed
to emerge. Although IgE antibody specific for all recognized chemical
respiratory allergens has been demonstrated, it is not uncommonly the case
that individuals displaying symptoms of pulmonary hypersensitivity have
been reported to lack demonstrable IgE. This may suggest that
immunological processes independent of IgE antibody may play a decisive
role in the induction of respiratory sensitization. An alternative explanation
is that inappropriate or insensitive techniques have been employed for
serological analysis and that IgE antibody may be associated more
commonly than suspected previously with chemical respiratory allergy. In
this context it is relevant that it has been found that positive skin prick
tests can be provoked in patients sensitized to acid anhydrides who, on the
basis of radioallergosorbent tests (RAST), were found to lack measurable
levels of serum IgE antibody (Drexler et al., 1993). Despite the absence of
formal confirmation that there exists a universal causal relationship
between specific IgE and pulmonary hypersensitivity induced by chemicals,