Secondary immune response is mediated by
**Core Concept**
The secondary immune response is a type of immune response that occurs upon subsequent exposure to the same antigen, characterized by a more rapid and effective response due to the presence of memory cells. This response is mediated by T and B lymphocytes that have been activated during the primary immune response and have differentiated into memory cells.
**Why the Correct Answer is Right**
During the secondary immune response, memory B cells (also known as plasma cells) rapidly proliferate and differentiate into antibody-secreting cells, producing large amounts of specific antibodies that can neutralize the pathogen. This is due to the activation of the T-cell dependent pathway, where T helper cells (Th2) activate B cells through the CD40-CD40L interaction, leading to the production of cytokines such as IL-4 and IL-6 that promote antibody production. Additionally, the presence of memory T cells (such as CD4+ and CD8+ T cells) helps to coordinate and amplify the immune response.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect as the primary immune response is mediated by naive T and B cells, which are not yet activated or differentiated into memory cells.
* **Option B:** This option is incorrect as the innate immune response is a non-specific response that occurs immediately upon exposure to a pathogen, and does not involve the activation of memory cells.
* **Option C:** This option is incorrect as the humoral immune response is a specific type of immune response mediated by antibodies, but it does not specifically refer to the secondary immune response.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that the secondary immune response is characterized by a more rapid and effective response, often resulting in the resolution of symptoms within a shorter timeframe compared to the primary immune response.
**Correct Answer:** C.