Reese, Sven; Dalamani, Grammatia; Kaspers, Bernd
(9. March 2006):
The avian lung-associated immune system. A review.
In: Veterinary Research, Vol. 37, No. 3: pp. 311-324
The lung is a major target organ for numerous viral and bacterial diseases of poultry. To
control this constant threat birds have developed a highly organized lung-associated immune
system. In this review the basic features of this system are described and their functional properties
discussed. Most prominent in the avian lung is the bronchus-associated lymphoid tissue (BALT)
which is located at the junctions between the primary bronchus and the caudal secondary bronchi.
BALT nodules are absent in newly hatched birds, but gradually developed into the mature structures
found from 6–8 weeks onwards. They are organized into distinct B and T cell areas, frequently
comprise germinal centres and are covered by a characteristic follicle-associated epithelium. The
interstitial tissue of the parabronchial walls harbours large numbers of tissue macrophages and
lymphocytes which are scattered throughout tissue. A striking feature of the avian lung is the low
number of macrophages on the respiratory surface under non-inflammatory conditions. Stimulation
of the lung by live bacteria but not by a variety of bacterial products elicits a significant efflux of
activated macrophages and, depending on the pathogen, of heterophils. In addition to the cellular
components humoral defence mechanisms are found on the lung surface including secretory IgA.
The compartmentalisation of the immune system in the avian lung into BALT and non BALTregions
should be taken into account in studies on the host-pathogen interaction since these
structures may have distinct functional properties during an immune response.