In vivo, the levels of expression of GM-CSF in the lungs during Mtb infection increase steadily during the acute and chronic stage of infection (Higgins et al., 2008) whereas lack of GM-CSF results in uncontrolled replication of Mtb in the lungs but not in spleen (Gonzalez-Juarrero et al., 2005; Szeliga et al., 2008). Here, CSF2 is linked to infection.