**Question:** Russell body is found in -

**Core Concept:** Russell bodies are specific subcellular structures that play a crucial role in the immune response. They are primarily composed of immunoglobulin light chains and are associated with plasma cells and B cells.

**Why the Correct Answer is Right:**

Russell bodies are mainly found in plasma cells and B cells, which are immune cells that produce antibodies. These cells are part of the adaptive immune system, responsible for responding to specific pathogens. The presence of immunoglobulin light chains within Russell bodies indicates their connection to the immune response.

**Why Each Wrong Option is Incorrect:**

A. Neurons (A) and glial cells (B) are not involved in the immune response, making options A and B incorrect. Neurons are part of the peripheral nervous system, while glial cells support neurons. In contrast, plasma cells and B cells are involved in the adaptive immune response.

C. T cells (C) are a different type of immune cell, involved in cell-mediated immunity, not producing antibodies or forming Russell bodies.

D. Macrophages (D) are part of the innate immune system, scavenging pathogens and cellular debris. Although they can engulf foreign substances, they do not form Russell bodies containing immunoglobulin light chains, which are exclusive to plasma cells and B cells.

**Clinical Pearl:**

Understanding the correct cellular context of Russell bodies is essential for proper interpretation of their presence in clinical settings. For example, the detection of Russell bodies in tissue biopsies may indicate plasma cell dyscrasias (e.g., myeloma, monoclonal gammopathy) or certain lymphoproliferative disorders. Detecting these structures can help differentiate between benign and malignant plasma cell disorders, guiding diagnostic and treatment decisions.

**Correct Answer:** D. Macrophages

**Core Concept:** Macrophages are part of the innate immune system, playing a crucial role in phagocytosis (engulfing pathogens and cellular debris) and antigen presentation. In the context of Russell bodies, macrophages do not form these structures containing immunoglobulin light chains, which are exclusive to plasma cells and B cells. Hence, option D is the correct answer.