Which of the folloss mg features is not shared between `T cells’ and ‘II cells’
**Core Concept**
T cells and B cells are two main types of lymphocytes that play crucial roles in the adaptive immune response. Both T cells and B cells have unique characteristics and developmental processes, but they also share some common features. Understanding the similarities and differences between T cells and B cells is essential for comprehending the immune system's functioning.
**Why the Correct Answer is Right**
T cells undergo a process called negative selection during their development in the thymus, but not positive selection. Positive selection is a process where T cells are selected based on their ability to recognize self-MHC molecules, ensuring that only T cells with self-tolerant receptors are allowed to mature. In contrast, B cells undergo a process called positive selection in the bone marrow, where they are selected based on their ability to recognize self-antigens. The correct answer is A, as positive selection is not a shared feature between T cells and B cells.
**Why Each Wrong Option is Incorrect**
**Option B:** Class I MHC expression is a shared feature between T cells and B cells. Both types of lymphocytes recognize antigens presented by Class I MHC molecules, which are expressed on the surface of almost all nucleated cells.
**Option C:** Antigen-specific receptors are also a shared feature between T cells and B cells. T cells have T cell receptors (TCRs), while B cells have B cell receptors (BCRs), both of which are responsible for recognizing specific antigens.
**Option D:** All of the above is incorrect because the correct answer is A, positive selection during development, which is not shared between T cells and B cells.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that the immune system has mechanisms to prevent autoimmunity, such as negative selection in T cells and positive selection in B cells. This ensures that the immune system only responds to non-self antigens and not to self-antigens.
**Correct Answer Line**
✓ Correct Answer: A. Positive selection during development.