When germ-free mice are inoculated with respiratory symbiotic microbes such as Staphylococcus aureus and Staphylococcus epidermidis, the granulocyte macrophage colony stimulating factor (GM-CSF) signaling pathway and NLRs are activated, and the NLRs signaling pathway improves resistance to infection (Brown et al., 2017). Here, CSF2 is linked to infection.