In this task, you are given a sentence. You are expected to recognize the name of gene or protein. Although there might be several correct answers, you need to write one of them.

 Bone resorption is regulated by the immune system , where T - cell expression of RANKL ( receptor activator of nuclear factor ( NF ) - kappaB ligand ) , a member of the tumour - necrosis factor family that is essential for osteoclastogenesis , may contribute to pathological conditions , such as autoimmune arthritis .
nuclear factor