The avian respiratory immune system

The respiratory tract is continuously challenged by aerosols which contain particulate material and nonpathogenic microorganisms and may also carry pathogens of significant economic importance for the poultry industry such as MDV, avian influenza virus, or avian pathogenic Escherichia coli. To control such pathogens, several layers of nonspecific and specific defense mechanisms develop shortly before and after hatch. Cells of the myeloid lineage are the first cells to be found throughout the respiratory tract while the appearance of lymphocytes follows the release pattern of the thymus and bursa of Fabricius. In addition, several organized lymphoid structures exist in the paraocular, nasal, and lung tissues. The morphological features of this system have been described in recent years, but their functional features are still poorly understood. © 2022 Elsevier Ltd. All rights reserved.