TLR4 and infection: These results suggest E. coli infection upregulates Siglec-E expression in neutrophils via the TLR4/MyD88/JNK/NF-κB/AP-1 signaling pathway, whereas infection with L. monocytogenes downregulates Siglec-E expression in neutrophils via the TLR2/RANKL/TRAF6/Syk signaling pathway.