Applications of the CSF1R-transgenic birds to study the avian respiratory-associated immune responses. Intratracheal application of red carboxlylated fluorescence beads in a MacGreen reporter bird (A–D) and APEC-GFP in a MacRed reporter bird (E–F). Thirty mins post-intratracheal administration, beads (1 µm) are deposited at the openings of the SB (A). At 3 h post administration, the beads are co-located with the capillaries of air sacs (B). Visualisation of binding and phagocytosis of particles in the lung demonstrated by binding of beads to the epithelial cells of the BALT (C; 0.1 µm beads, thirty min post-administration,) and intracellular beads in CSF1R-eGFP+ cells (D; 1 µm beads, 3 h post-administration). An example of host–pathogen interactions is demonstrated in E–F. Thirty min after intra-tracheal administration, bacteria can be found bound to FAE of the lung (E) and APEC-GFP uptake by CSF1R-mApple+ cells in the parabronchus can be visualized 1 day post-infection (F–G–Gi). The epithelial layer is indicated by yellow dashed line.