**Question:** EAC rosettes are formed by

A. B cells
B. T cells
C. Lymphocytes
D. Monocytes

**Core Concept:** EAC rosettes are a technique used in haematology to study the interaction between erythrocytes (red blood cells) and immune cells, particularly B cells.

**Why the Correct Answer is Right:** EAC rosettes are formed when sheep red blood cells (SRBCs) are incubated with human peripheral blood mononuclear cells (PBMCs), which contain B cells. The SRBCs are coated with antibodies specific to human immunoglobulin (IgG or IgM) produced by the B cells. The B cells bind to the SRBCs, forming rosettes.

**Why Each Wrong Option is Incorrect:**

A. B cells are correct, but they are not the only cell type capable of forming rosettes.
B. T cells do not form rosettes with SRBCs, as they lack the necessary antibodies on their surface.
C. Lymphocytes are a general term for white blood cells, not specific to the cell type forming rosettes.
D. Monocytes are a subset of white blood cells, not involved in forming rosettes with SRBCs.

**Why EAC Rosettes are Clinically Relevant:** EAC rosettes have clinical applications in understanding the immune system and diagnosing certain disorders, such as agammaglobulinemia and common variable immunodeficiency. These conditions involve reduced B cell numbers or function, leading to decreased formation of EAC rosettes. Understanding the role of EAC rosettes in diagnosing these immunodeficiencies highlights the importance of this technique in clinical immunology.

**Core Concept:** Erythrocytes (red blood cells) are the core component of an EAC rosette. Antibodies produced by B cells bind to the SRBCs, and the B cells are the binding partner.

**Why the Correct Answer is Right:** The correct answer is B cells, as they are the cells that produce antibodies and bind to the SRBCs, forming the rosettes. The other options are not involved in the rosette formation process.

**Why Each Wrong Option is Incorrect:**

A. T cells do not form rosettes with SRBCs, as they lack the necessary antibodies on their surface.
B. Monocytes are a subset of white blood cells but are not involved in forming rosettes with SRBCs.
C. Lymphocytes are a general term for white blood cells, not specific to the cell type forming rosettes with SRBCs.
D. Neutrophils are a type of white blood cell, but they are not involved in forming rosettes with SRBCs.

**Clinical Application:** Erythrophagocytosis is the process by which neutrophils engulf and destroy SRBCs, not form rosettes with them. Understanding the role of EAC rosettes in diagnosing immunodeficiencies highlights the importance of this technique in clinical immunology.