CTTN and infection: Fig. 4A shows that the maximal level of phospho-Tyr421 cortactin was observed at 1 h of infection with live bacteria. Similar cortactin phosphorylation levels were observed during infection of a phagocytic cell (Fig. S2B). In contrast, the level of this form of phosphorylated cortactin did not change significantly when the infection was carried out with heat-killed C. burnetii (Fig. 4B). These results suggest that C. burnetii induces phosphorylation of cortactin on Tyr421 early during infection.