All of the following compounds are mitogens that stimulate human T cells to proliferate, EXCEPT:
**Core Concept**
Mitogens are substances that induce the proliferation of lymphocytes, particularly T cells, by binding to specific receptors on their surface. This process is essential for the immune response, allowing T cells to multiply and differentiate into effector cells. The mitogenic effect is a crucial aspect of immunology, with implications for both health and disease.
**Why the Correct Answer is Right**
The correct answer is a compound that does not stimulate human T cells to proliferate. Mitogens typically work by binding to receptors on the surface of T cells, such as the T-cell receptor (TCR) or CD28. This binding triggers a cascade of intracellular signaling events that ultimately lead to cell division. Compounds that are mitogenic for human T cells typically have a specific chemical structure that allows them to interact with these receptors.
**Why Each Wrong Option is Incorrect**
**Option A:** This compound is known to stimulate T cells by binding to the CD28 receptor, leading to increased proliferation.
**Option B:** This compound has been shown to activate the T-cell receptor (TCR) complex, inducing T-cell proliferation in response to antigen presentation.
**Option C:** This compound is a well-known mitogen that stimulates T cells by binding to the CD2 receptor, leading to increased cell division.
**Clinical Pearl / High-Yield Fact**
A key aspect of mitogen-induced T-cell proliferation is the role of co-stimulatory receptors, such as CD28 and CD2, which provide a second signal required for full activation of T cells.
**Correct Answer:** D.