<prompt> The main cytokine, involved in erythema nodusum leprosum ENL reaction is:Interleukin-2Interferon-gammaTumor necrosis factor-alphaMacrophage colony stimulating factor  <response>: Ans is c i.e. Tumor necrosis factors Ref: Harrison 16the p 968,969Erythema nodosum leprosum or Type II lepra reaction occurs exclusively in patients near the lepromatous end of leprosy spectrum. In about 90 cases Erythema nodosum leprosum follows institution of chemotherapy. Immunopathology of Erythema Nodosum LeprosumENL is thought to be a consequence of immune complex reaction. Elevated levels of tumor necrosis factor TNF have been demonstrated in erythema nodosum leprosy.It is thought that TNF plays a central role in the pathobiology of this syndrome. 