Presence of DNA extracellular traps but not MUC5AC and MUC5B mucin in mucoid plugs/casts of infectious laryngotracheitis virus (ILTV) infected tracheas of chickens

Although it has been speculated that the tracheal obstructions and asphyxiation during acute infectious laryngotracheitis (ILT) are due to mucoid plugs/casts formed by mucus hypersecretion, there are no reports demonstrating this. Hence, in the present study, we first examined if the main respiratory mucins, MUC5AC and MUC5B, are expressed in the mucosae of larynx, trachea and bronchi of mock-inoculated and ILTV infected chickens. Second, the tracheas with plugs/casts were stained for mucins (MUC5AC and MUC5B) and nuclear material (traps). MUC5AC and MUC5B were produced by the mucosae of larynx, trachea and bronchi of mock-inoculated chickens. Interestingly, MUC5AC and MUC5B were exclusively present in the dorsal tracheal region of the cranial and middle part of trachea of mock-inoculated chickens. In ILTV infected chickens, the tracheal lumen diameter was almost 40% reduced and was associated with a strongly increased tracheal mucosal thickness. MUC5AC and MUC5B were scarcely observed in larynx, trachea and bronchi, and in tracheal plugs/casts of ILTV infected birds. Surprisingly, DNA fibrous structures were observed in connection with nuclei of 10.0 ± 7.3% cells, present in tracheal plugs/casts. Upon inoculation of isolated blood heterophils with ILTV, DNA fibrous structures were observed in 2.0 ± 0.1% nuclei of ILTV inoculated blood heterophils at 24 hours post inoculation (hpi). In conclusion, the tracheal obstructions and suffocation of ILTV infected chickens are due to a strong thickening of the mucosa (inflammation) resulting in a reduced tracheal lumen diameter and the presence of mucoid plugs/casts containing stretched long DNA-fibrous structures (traps) but not MUC5AC and MUC5B mucins.