**Question:** Typical cell in lymphoid tissue of a case of measles shown in the illustration is:

A. Germinal center cell
B. T cell
C. B cell
D. Plasma cell

**Correct Answer:** C. B cell

**Core Concept:** In infectious diseases like measles, lymphocytes play a crucial role in mounting a specific immune response against the causative pathogen. Measles is caused by the measles virus, which belongs to the Paramyxoviridae family. The immune response involves both B cells (B lymphocytes) and T cells (T lymphocytes).

**Why the Correct Answer is Right:** In lymphoid tissue during measles infection, B cells differentiate into plasma cells and antibody-secreting cells. These cells produce measles-specific antibodies that neutralize the virus and help eliminate infected cells. In contrast, T cells primarily participate in cell-mediated immunity, helping to eliminate infected cells and prevent viral replication. Germinal center cells represent a specialized B cell area within lymphoid tissue where their activation, proliferation, and affinity maturation occur. Plasma cells are responsible for producing high-affinity antibodies but are not the primary cell type in the lymphoid tissue of a case of measles. T cells are not the primary cell type in the lymphoid tissue of a case of measles; their role is more relevant to cell-mediated immunity and not directly involved in neutralizing the virus.

**Why Each Wrong Option is Incorrect:**

A. Germinal center cell: Although germinal center cells are involved in the immune response, they do not represent the primary cell type in lymphoid tissue during measles infection. B cells are the primary cell type responsible for neutralizing the virus.

B. T cell: T cells are crucial for cell-mediated immunity, helping to eliminate infected cells, but they are not the primary cell type in the lymphoid tissue of a case of measles. B cells are the primary cells involved in neutralizing the virus.

C. B cell: B cells are the primary cells involved in the production of measles-specific antibodies and neutralizing the virus within the lymphoid tissue. They differentiate into plasma cells that secrete measles-specific antibodies.

D. Plasma cell: Plasma cells are responsible for producing high-affinity antibodies but are not the primary cell type in the lymphoid tissue of a case of measles. B cells are the primary cells involved in neutralizing the virus.

**Clinical Pearls:**

Measles infection is characterized by the presence of B cells and plasma cells within the lymphoid tissue, producing measles-specific antibodies. These cells are the primary effectors in neutralizing the virus and clearing the infection. T cells, while crucial for cellular immunity, are not the primary cell type involved in neutralizing measles virus.