CD95, also known as Fas or Apo-1, is a type I transmembrane protein that plays a critical role in the immune system. It is a member of the tumor necrosis factor receptor (TNFR) superfamily and is expressed on various cell types, including T and B lymphocytes, thymocytes, and some non-lymphoid tissues. It binds to its ligand, CD95L (FasL), which is a type II transmembrane protein primarily expressed on activated T cells and natural killer (NK) cells. The interaction between CD95 and CD95L can induce apoptosis, which is crucial for the elimination of infected or transformed cells and for maintaining tissue homeostasis. This interaction leads to the formation of the death-inducing signaling complex (DISC), which activates caspases and ultimately results in cell death. While CD95 is known for its pro-apoptotic function, it can also transmit non-apoptotic signals that promote inflammation and carcinogenesis. The receptor can switch from an apoptotic function to an inflammatory role, depending on the cellular context and signaling pathways activated.
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