Given that GM-CSF promotes cytokine production in monocytes stimulated through TLR2 alone (Fig. 1), we hypothesized that initial TLR signaling is required for GM-CSF to augment cytokine expression during Legionella infection, as Legionella is known to activate TLR signaling (45, –, 52). The gene discussed is TLR2; the disease is legionellosis.