THE CHALLENGES FOR IMMUNOLOGY
Although great advances have been achieved in the field of porcine immunology
during the last years, there are still some important issues that require more
research and development.
What is still not known?
What we know about immunology, as in most sciences, is constantly moving forward together
with improvements in technology. Although important progress has been achieved in the last
years, there are still many issues that are not yet well known about this science. In this chapter we
will review some of these challenges, starting with the cells of the immune system and ending
with the protective mechanisms.
There are still some unknown areas that need
to be cleared up in the field of the cells of the
immune system. this is true regarding the
receptors of lymphocytes  and , and
antigen presenting cells APC), especially
dendritic cells, that may help us to better
understand the mechanisms of the cell
cooperation during the development of the
immune response.
Diagram of the cellular collaboration during the adaptive immune
response.
Another challenge for porcine immunology is the better
understanding of the mechanisms involved in the
immunity of the mucosa, regarding to the infection
routes and the transportation of antigens that allow an
enhanced immune response.
Regarding the porcine immunoglobulins; a better
knowledge of the immunoglobulin IgE is necessary. Up
til now it has only been identified in an indirect way. Also,
the existence of porcine IgD needs to be confirmed, and
the available information about the protective role of
immunoglobulin IgA must be enlarged.
Porcine immunology needs a better understanding of
cytokines; only 19 porcine cytokines have been
cloned. One of the aspects requiring more research is
their role in the innate and adaptive immune response, in
the hematopoiesis and in lymphocyte activation.
ANTIGEN PRESENTATION IN THE INDUCING AREA OF
THE MUCOSA. Antigens entering the gut epithelial cell are
readily destroyed by the lysosomes. However, those antigens
that are captured by the M cells are transported, without
being destroyed, and later presented to the intra-epithelial
lymphocytes. Then, they are transported to the lymphatic
nodes.
Cytokines play a mayor role in the innate immune
response due to the mechanisms of direct action against
the infectious agent (they prevent the infection of the
cells by the viruses) or by mechanisms of cell activation
(NK and macrophages) which at the same time induces
the release of more cytokines.
One of the functions of cytokines is the attraction of the different cells
of the immune system.
Finally, there is a need to improve what we
know about the immune mechanisms that
work against infectious and parasitic
agents. Parasites, due to their complex
antigenic structure and their different life
cycles, use different strategies to evade the
immune response by using intracellular
infections or antigenic variations that are not
yet well understood. Parasite immunology is
one of the pending subjects. In addition, more
effective vaccines against bacterial and
viral agents must be achieved, which means
more research should be performed in this
area. DNA vaccines will in the near future,
represent an excellent option.
Diagram showing the different types of new generation vaccines.
Which way will immunological studies go?
The development of new technologies will allow a better understanding of the subjects mentioned above.
The development of genetic engineering, that allow the cloning and expression of different genes (thus
knowing the role of the proteins that they codify), as well as new transgenic experimental animals,
either knock-out animals (which have some of their genes suppressed and thus do not express certain
proteins)
or animals in which a new gene has been
incorporated, are some of the new
technologies now available that will help to
better understand the immune response.
We must not forget the essential role that
monoclonal antibodies play in the study of
populations and subpopulations of
lymphocytes and in the study of epitopes from
different antigens. Also, syngenetic animals
are important when studying the
histocompatibility system. Thanks to all
these new techniques the advances in the
knowledge of porcine immunology will keep
moving forward.
Diagram showing the production of monocolonal antibodies.
Which will be the future role of pigs?
Nowawdays, porcine production is one of the main sources of material for the meat industry in the
European Union, and is an important part of the total agricultural production. This production will be
increased in the future thanks, among other factors, to increased production in Spain. All this makes the
pig a strategic animal in future economic development; therefore research on this species is of
vital importance. Moreover, pigs are not only considered as a source of protein, but also as a source of
organs for transplants in the humans species.
Xenografts (grafts between xenogeneic members of different species) are an alternative due to low
numbers of available human organs for transplants. Donations are insufficient even in Spain, which
has one of the highest organ donation rates in the world. Among the different animal species
considered as possible donors (primates, baboons), pigs have some important advantages.
Some of these advantages are: they breed
easily, their size is compatible to human
size, There is a smaller risk of crossinfections (excepting endogen porcine
retroviruses; the sanitary consequences
are now being studied) and the possibility
exists of producing poly-transgenic pigs
that express different genes in order to
avoid the acute rejection of the vascular
rejection, which are nowadays the main
problems of xenografts. There already are
transgenic pigs regarding DAF (Decay
Accelerating Factor). DAF inhibits the
production of cobertasas of C3 and C5,
avoiding the activation of the complement
by both pathways during the hyperacute
rejection.
Electronic microscopy image of retrovirus.
From what has been explained above, we can suggest that research on pigs will be, during the following
years, one important issue in the scientific strategy in most developed countries.
It seems that transgenic pigs and especially poly-transgenic ones
seem to be the candidate donors of xenografts for the human species.
Picture of a baboon. This species was considered as the
main candidate for xenografts in humans.