Okay, let's tackle this question. The question is about EAC rosette formation and which immune cell it's associated with. First, I need to recall what EAC rosettes are. EAC stands for Erythrocyte-antibody-complement rosettes. So, this is probably a test for certain cell surface markers.

I remember that T cells and B cells have different markers. EAC rosettes are formed when sheep red blood cells bind to T cells via CD2 (LFA-3 interaction). Wait, but EAC rosettes specifically involve complement. Oh right, maybe it's about the Fc receptors. B cells have Fc receptors for IgG, so when there's an antibody and complement involved, maybe B cells form EAC rosettes. Wait, but T cells form E rosettes (just erythrocytes), while EAC would involve complement. Let me check.

E rosettes are T cells binding to sheep RBCs via CD2. EAC rosettes involve IgG antibodies and complement, so the cell must have both Fc and C3b receptors. Macrophages and B cells have these. But B cells primarily. Wait, B cells have Fc receptors for IgG, so when the RBCs are coated with antibody and complement, B cells can bind them. So EAC rosette formation is a property of B cells. Therefore, the correct answer would be B cells. The options probably list B cells as one of the choices. The distractors might be T cells, NK cells, or macrophages. Let me make sure. T cells would form E rosettes, not EAC. Macrophages might have Fc and complement receptors but are not typically tested this way in rosette assays. So the answer is B cells.

**Core Concept**
EAC (Erythrocyte-Antibody-Complement) rosette formation identifies immune cells expressing **Fcγ receptors** and **complement receptors (CR1/CD35)**. This assay detects cells capable of binding antibody-coated erythrocytes via these receptors, a hallmark of **B lymphocytes** due to their role in antibody production and complement interaction.

**Why the Correct Answer is Right**
B cells express **FcγRII (CD32)** and **CR1 (CD35)**, allowing them to bind IgG-coated erythrocytes (EAC rosettes). This binding is critical for B-cell activation via antigen-antibody-complement complexes. T cells lack these receptors and form simple E rosettes (via CD2/LFA-3), while macrophages and NK cells do not demonstrate this specific rosette formation in standard assays.

**Why Each Wrong Option is Incorrect**
**Option A:** T cells form E rosettes (CD2-mediated), not EAC rosettes.
**Option C:** Macrophages express Fc and CR1 but are not EAC rosette-positive in standard assays.
**Option D:** NK cells lack FcγRII and CR1 required for EAC rosette formation.

**Clinical Pearl / High-Yield Fact**
EAC rosette assays distinguish **B cells** (positive) from **T cells** (E rosette-positive

✓ Correct Answer: A. T cells