Which one among the following organs in humans is not involved in elicitation of immune response?

The immune system consists of primary and secondary lymphoid organs. The thymus is a primary lymphoid organ where T-cell lymphocytes mature and coordinate innate and adaptive immune responses [4]. The spleen and lymph nodes are secondary lymphoid organs that act as filters; the spleen traps blood-borne antigens to initiate immune responses, while lymph nodes filter lymph and trigger antibody production [4]. In contrast, the brain is traditionally considered an "immunologically privileged" organ [2]. It is protected by the blood-brain barrier, which regulates immune cell recruitment and limits the entry of monocytes and lymphocytes [2]. While the brain has resident microglia and specialized neuroimmune interactions at its borders, it is not a lymphoid organ involved in the primary elicitation or generation of systemic immune responses like the thymus, spleen, or lymph nodes [1].

Sources

1. [4] https://www.ncbi.nlm.nih.gov/books/NBK279395/
2. [3] https://pmc.ncbi.nlm.nih.gov/articles/PMC3912742/
3. [2] https://www.nature.com/articles/s41423-023-01043-8
4. [1] https://www.sciencedirect.com/science/article/abs/pii/S1471490606003267