Biology Reference
In-Depth Information
a number of countries but is still present in tropical zones; therefore, two
general types of associations with allergy may currently be found: in
parasite-free zones, the lack of helminth-induced immunosuppression
may have contributed to the increase of allergic diseases. Besides, in
countries where helminthiases are still prevalent, ascariasis is a risk factor
or a protective factor for allergy; alternatives seem to be related to the
intensity of the infection, which in turn depend not only on the level of
exposure but also on the genetic background of the population. In addi-
tion, the existence of immunological cross-reactivity among molecules
from
Ascaris
and domestic mites, which are very frequent in tropical
zones, has special implications for the pathogenesis and diagnosis of
allergy. Therefore, since ascariasis, whether being present or absent, is, in
some way, related to the allergic responses, its impact is general and not
limited to underdeveloped countries in the tropics.
BASICS CONCEPTS OF THE ALLERGIC
RESPONSE: HOW SIMILAR IS IT TO THE
I
MMUNE RESPONSE TO ASCARIS
?
The allergic response is a complex trait influenced by several genetic
variants and characterized by a Th2-type hyper-responsiveness to envi-
ronmental allergens that may lead to severe inflammation in various
tissues, for example the lung of asthmatic patients. It includes a pro-Th2
immune activation of different cells through a variety of innate receptors
and signaling pathways;
1
the production of a number of cytokines, among
them IL-3, IL-4, IL-5, IL-9, and IL-13 from the cluster of chromosome
5q31-33, and others such as IL-33, IL-25, and thymic stromal lympho-
poietin (TSLP);
2
also the hyper-production of total and specific IgE anti-
bodies
3
and the parallel activation of cellular B and T regulatory
networks.
4,5
Epithelial and dendritic cells are involved from the very
beginning of this process and important in the definition of the Th2 char-
acter of the response.
6
The participation of the Th17
7
and Th9 responses in
this inflammatory process has been also documented
2
and that of Th1 is
mainly related to severe asthma.
8
In addition, some cytokines, such as
tumor necrosis factor alpha (TNFA-
) and IL-13, which are considered
important defense mechanisms against helminths,
9,10
are also activated
during the allergic response and act directly on the bronchial epithelium
and smooth muscle, increasing the effects of the IgE-mast cell-mediated
inflammation in the lung.
11
e
13
This property has been also described for
IL-17A.
14
The participation of innate type 2 cells such as natural helper cells,
nuocytes, and multipotent progenitor type 2 cells, originally described
in association with experimental helminth infections, is under intense
a
