Spleen and bone marrow cells were blocked with blocking solution (PBS with 10% goat serum and 20% FBS) containing anti-CD16/32 for 10 min at 4 °C and then stained with surface antibodies against CD11b and Ly6G for 30 min. Cells were then fixed and permeabilized using the Cytofix/Cytoperm Fixation/ Permeabilization solution kit (BD) and methanol and stained with PE Mouse Anti-ERK1/2 (pT202/pY204) for 30 min at room temperature (BD). Cells were then acquired on a BD LSRFortessa.