Annexin V on non-permeable cell is indicative of.?

Okay, let's tackle this question. The question is about Annexin V and its significance when the cell is non-permeable. First, I need to recall what Annexin V does. I remember that Annexin V is used in apoptosis detection. During early apoptosis, phosphatidylserine (PS) flips from the inner leaflet to the outer leaflet of the cell membrane. Annexin V has a high affinity for PS and binds to it, so when you use Annexin V with a fluorescent marker, you can detect cells undergoing apoptosis.

Now, the question mentions "non-permeable cell." That probably means that the cell membrane isn't compromised, so the cell isn't in late apoptosis or necrosis. In those cases, the membrane would be permeable, allowing propidium iodide to enter. So Annexin V binding to non-permeable cells would indicate early apoptosis. The options are probably something like early apoptosis, late apoptosis, necrosis, or something else. The correct answer is early apoptosis. The other options would be incorrect because late apoptosis and necrosis involve membrane permeability. Necrosis definitely has a broken membrane. Late apoptotic cells might also have some permeability. So the key here is that Annexin V is a marker for PS exposure, which occurs early, and the non-permeable cell means it's not necrotic or in late stages.

**Core Concept**
Annexin V binds to phosphatidylserine (PS) exposed on the cell surface during **early apoptosis**. Non-permeability indicates the cell membrane remains intact, distinguishing apoptosis from necrosis or late apoptosis.

**Why the Correct Answer is Right**
In early apoptosis, PS translocates from the inner to outer leaflet of the plasma membrane due to reduced aminophospholipid translocase activity. Annexin V, a calcium-dependent phospholipid-binding protein, selectively binds to PS. A non-permeable cell (excluded by propidium iodide) confirms the plasma membrane is intact, confirming **early apoptotic stage**.

**Why Each Wrong Option is Incorrect**
**Option A:** Necrosis involves membrane rupture and PS exposure via passive leakage, not regulated PS translocation.
**Option B:** Late apoptosis is marked by membrane permeabilization (e.g., by caspase-activated scramblase) and propidium iodide uptake.
**Option C:** Necrosis lacks PS translocation; PS exposure is secondary to cell lysis.

**Clinical Pearl / High-Yield Fact**
Annexin V flow cytometry combined with propidium iodide staining is the gold standard to differentiate **early vs. late apoptosis**. Remember: **"Annexin V + PI- = early apoptosis; Annexin V + PI+ = late apoptosis/necrosis."**

**Correct Answer: C. Early apoptosis**

✓ Correct Answer: A. A. Apoptosis