Abstract
The respiratory tract is a key organ for many avian pathogens as well as a major route for vaccination in the poultry industry. To improve immune responses after vaccination of chickens through increased uptake of vaccines and targeting to antigen presenting cells, a better understanding of the avian respiratory immune system is required. Transgenic MacReporter birds were used expressing a reporter gene (eGFP or mApple) under the control of the CSF1R promoter and enhancer in cells of the mononuclear phagocyte (MNP) lineage to visualize the ontogeny of the lymphoid tissue, macrophages and dendritic cells, in the trachea, lung and air sac of birds from embryonic day 18–63 weeks of age. Small aggregates of CSF1R-transgene+ cells start to form at the openings of the secondary bronchi at 1 week of age, indicative of the early development of the organised bronchus-associated lymphoid tissue. Immunohistochemical staining revealed subpopulations of MNPs in the lung, based on expression of CSF1R-transgene, CD11, TIM4, LAMP1, and MHC II. Specialised epithelial cells or M cells covering the bronchus-associated lymphoid tissue expressed CSF1R-transgene and type II pneumocytes expressed LAMP1 suggesting that these epithelial cells are phagocytic and transcytose antigen. Highly organised lymphoid tissue was seen in trachea from 4 weeks onwards. Throughout the air sacs at all ages, CSF1R-transgene+ cells were scattered and at later stages, CSF1R-transgene+ cells lined capillaries. These results will serve as a base for further functional characterization of macrophages and dendritic cells and their role in respiratory diseases and vaccine responses.
Highlights
In the poultry industry, vaccines are frequently delivered via spray and aerosol, providing an economical, efficient and reliable method for immunisation of a large number of birds
Development and distribution of mononuclear phagocytes and germinal centers in the lung of colony stimulating factor 1 receptor (CSF1R)‐transgenic birds The distribution of CSF1R-transgene expressing cells was examined in lungs of MacReporter birds of different ages by whole mount microscopy
From 4 weeks of age onwards, germinal center (GC) are observed within these lymphoid follicles, and they are characterized by tightly packed aggregates of CSF1Rtransgene+ cells (Figures 2E–H)
Summary
Vaccines are frequently delivered via spray and aerosol, providing an economical, efficient and reliable method for immunisation of a large number of birds. The respiratory tract is a major portal of entry of pathogens that are of economic or zoonotic importance, such as avian influenza virus (AIV), infectious bronchitis virus (IBV), Newcastle Disease virus and avian pathogenic Escherichia coli (APEC). Little is known about the ontogeny and function of the immune cells in the avian respiratory tract. Nonspecific defense mechanisms, such as aerodynamic filtration, mucociliary clearance and antimicrobial substances are the first line of defense of the avian respiratory tract [1,2,3]. The avian respiratory system differs significantly from mammals. Birds have relatively rigid lungs, lack a diaphragm and the lung opens into 9 air sacs that function as bellows, with a unidirectional air flow pattern that affects the deposition of particles [4,5,6]
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