TLR4 and gram-negative bacterial infections: More recently, Zhang et al. show that Gram-negative bacterial infection or LPS stimulation can elevate the expression of VEGFR3 and VEGF-C through TLR4-NF-kB signaling in macrophage, whereas VEGF-C ligation of VEGFR3 forms a negative feedback loop to inhibit TLR4-induced inflammatory responses.