We found no significant YopM-related differences in Tnfα message levels at 3 h p.i., perhaps because of the opposing effects on Egr1. It is meaningful to test for Tnfα message this early in infection, because it can be induced within an hour in response to stimuli (Espel et al., 1996; Raabe et al., 1998), and a significant downregulating effect was observed at 3 h by Rüter et al. (2010) in HL60-derived macrophages treated with pure YopM. Here, TNF is linked to infection.