It is possible that the protective role of GM-CSF in the murine pneumonia model could be facilitated by the presence of opsonins such as antibodies specific for P. aeruginosa or lung collectins, such as SP-A, which could promote phagocytic uptake and cellular activation, or the accumulation of monocytes/macrophages in the infected lungs of vaccinated animals [60]. This evidence concerns the gene CSF2 and susceptibility to pneumonia measurement.