Which of the following organ is not involved in elicitation of immune response?

Options

A. Thymus
B. Spleen
C. Lymph nodes
D. Brain

Answer

To determine which organ is not involved in the elicitation of immune response, we can analyze the options provided: thymus, spleen, lymph node, and brain.

### Step-by-Step Solution:

1. **Identify the Role of Each Organ:**
- **Thymus:** This organ is a primary lymphoid organ where T-cells mature. It plays a crucial role in the immune response.
- **Spleen:** This is a secondary lymphoid organ that filters blood and helps in the activation of immune responses against blood-borne pathogens.
- **Lymph Node:** These are also secondary lymphoid organs that filter lymph and are sites where immune responses can be initiated.

2. **Assess the Brain's Role:**
- **Brain:** The brain is part of the central nervous system and does not have a direct role in the immune response. It primarily functions in processing information and coordinating body functions.

3. **Conclusion:**
- Since the thymus, spleen, and lymph nodes are all involved in the immune response, while the brain is not, the correct answer to the question is the **brain**.

### Final Answer:
**Brain**

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