TLR4 and Behcet disease: Another study showed that NE activates the epidermal growth factor receptor [27] and induces the expression of IL-8 via toll-like receptor 4 [28] One of the studies showed that the elevated level of homocysteine in BD patients [29] is responsible for overproduction of nitric oxide from endothelial cells, induces expression of chemoattractants by oxygen free radicals, and induces IL-6, IL-8, and TNF-α [30, 32].