Elevated levels of interleukin-1β (IL-1β), interleukin-6 (IL-6), interleukin-8 (IL-8), tumor necrosis factor α (TNF-α), soluble interleukin-2 receptor (sIL-2R), and nitric oxide (NO) correlating with both the presence and the severity of DR were found in the serum of patients with type 2 diabetes [26,40,41]. Here, TNF is linked to type 2 diabetes mellitus.