I firmly believe that a full understanding of the immune system will be acquired only through comparative analysis of its structure, function and physiology in a multitude of different species.,
Immunology is not just restricted to investigations on the immune systems of mice and humans.
Historically, studies on other species have contributed greatly to the development of immunological understanding. Amongst these other species, birds have provided an invaluable model
for investigating basic immunological mechanisms. Birds have also played a crucial role in the
development of vaccinology, and they still do to this day. The fi rst attenuated vaccine discovered by Pasteur was directed against fowl cholera, a poultry disease. Likewise the first widely used vaccine against a naturally occurring cancer, Marek’s disease, was developed for the poultry industry. The current threat from avian infl uenza reminds us of the necessity for gaining a
thorough understanding of the avian immune system in order to develop novel and effective strategies for control.
Birds have many immunological mechanisms in common with mammals but have evolved
a number of quite distinct strategies; they achieve the same goal through use of different mecha-
nisms. Some of their different physiological characteristics such as their lung ventilation system, significantly different from the mammalian one, may partly explain the pressures for the evolution of different mechanisms.
One key feature of research on the avian immune system has been the seminal contributions
it made on the key role of lymphocytes in adaptive immunity, graft-versus-host responses, delineation of the two major lymphocyte lineages – B cells and T cells – and gene conversion for developing the immunoglobulin repertoire. In addition the chicken major histocompatibility complex
(MHC) – the fi rst non-mammalian MHC to be sequenced – is compact, considerably smaller than
its mammalian counterpart, and strongly associated with resistance to certain infectious diseases.
No doubt the availability of the entire chicken genome sequence will help provide us with a more
precise picture and a better understanding of the avian immune system.
Birds have been described as living dinosaurs, as exemplifi ed by the discovery of dinobirds,
mainly in China. This discovery provides a major incentive to carefully study the avian immune
system and gain a better understanding of the rules of evolution. At the same time, we should
bear in mind that infections provide an important selection pressure and immunocompetence
is a valuable trait for the survival of a species.