Bronchoalveolar lavage fluid collection and measurement
The chickens were euthanatized and the cavity was opened by a midline incision. Then, the bronchoalveolar lavage fluid (BALF) were lavaged with sterile and ice of PBS (0.4 ml each time) for three times. After centrifuged at 2,000 g for 10 min at 4 °C, the supernatant was gathered to measure the concentration of total protein by BCA kits (Thermo, MA, USA).