Vet. Res. 37 (2006) 311-324
DOI: 10.1051/vetres:2006003

The avian lung-associated immune system: a review

Sven Reese^a, Grammatia Dalamani^a and Bernd Kaspers<sup>b

a</sup>  Institute for Animal Anatomy, Faculty of Veterinary Medicine, University of Munich, Germany
^b  Institute for Animal Physiology, Faculty of Veterinary Medicine, University of Munich, Veterinärstr. 13, 80539 München, Germany

(Received 13 June 2005; accepted 21 November 2005; published online 9 March 2006)

Abstract - 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 BALT-regions should be taken into account in studies on the host-pathogen interaction since these structures may have distinct functional properties during an immune response.

Key words: chicken / lung / BALT / avian respiratory phagocytes / IgA

Corresponding author: Bernd Kaspers Kaspers@tiph.vetmed.uni-muenchen.de

© INRA, EDP Sciences 2006