CD-95 has a major role in :
**Core Concept**
CD-95, also known as Fas or APO-1, is a receptor that plays a crucial role in the regulation of apoptosis, or programmed cell death. It is a member of the tumor necrosis factor receptor (TNFR) superfamily and is involved in the activation of caspase-8, leading to the initiation of the apoptotic cascade.
**Why the Correct Answer is Right**
The correct answer is related to the role of CD-95 in inducing apoptosis in response to binding with its ligand, FasL. This binding activates a series of downstream signaling events, including the activation of caspase-8 and the cleavage of various cellular substrates, ultimately leading to cell death. CD-95 is expressed on the surface of various cell types, including T cells, and its activation is a key mechanism of immune regulation and tolerance.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because CD-95 is not primarily involved in the regulation of cell proliferation. While CD-95 may have some indirect effects on cell growth, its major role is in the induction of apoptosis.
**Option B:** This option is incorrect because CD-28 is a costimulatory receptor that plays a role in T cell activation and proliferation, rather than apoptosis. CD-28 binds to its ligand, B7-1 or B7-2, to enhance T cell activation and proliferation.
**Option C:** This option is incorrect because CD-40 is a costimulatory receptor that plays a role in B cell activation and proliferation, rather than apoptosis. CD-40 binds to its ligand, CD-154, to enhance B cell activation and proliferation.
**Clinical Pearl / High-Yield Fact**
One important clinical correlation is that defects in the CD-95/Fas pathway have been associated with autoimmune diseases, such as autoimmune lymphoproliferative syndrome (ALPS). This highlights the importance of the CD-95 pathway in regulating immune tolerance and preventing autoimmune disease.
**Correct Answer:** C.