Immunology checkpoint — Which signaling molecule specifically triggers clonal expansion (division) of activated T lymphocytes?
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AFGF (Fibroblast growth factor)
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BInterleukin-2 (IL-2)
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CPDGF (Platelet-derived growth factor)
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DErythropoietin (EPO)
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ETNF-alpha (Tumor necrosis factor alpha)
Answer
Correct Answer: Interleukin-2 (IL-2)
Explanation
Introduction / Context:Following antigen recognition and costimulation, T cells require cytokine signals to proliferate. Identifying the principal autocrine growth factor for T cells is a staple concept in basic immunology and vaccine science.
Given Data / Assumptions:
- Activated T cells upregulate the high-affinity IL-2 receptor (CD25).
- IL-2 promotes clonal expansion and survival of effector and regulatory T cells.
- Other growth factors primarily target non-lymphoid cells.
Concept / Approach:Interleukin-2 (IL-2) acts in an autocrine and paracrine manner to drive T-cell proliferation. The IL-2/IL-2R axis is central to adaptive immune responses and is targeted therapeutically in transplantation and cancer immunotherapy.
Step-by-Step Solution:
Determine which listed factor is a T-cell growth cytokine.Match IL-2 to T-cell clonal expansion after activation.Exclude growth factors mainly affecting fibroblasts, platelets, erythroid cells, or proinflammatory signaling without primary mitogenic effect on T cells.Verification / Alternative check:Classical experiments show exogenous IL-2 drives T-cell proliferation in culture; blocking IL-2/IL-2R signaling impairs clonal expansion in vivo.
Why Other Options Are Wrong:
- a/c: FGF and PDGF stimulate mesenchymal and vascular cells rather than T cells.
- d: EPO acts on erythroid progenitors in bone marrow.
- e: TNF-alpha is proinflammatory but not the primary mitogen for T-cell clonal expansion.
Common Pitfalls:Confusing general growth factors with lymphocyte-specific cytokines; overlooking the requirement for IL-2 receptor upregulation (CD25) after activation.
Final Answer:Interleukin-2 (IL-2)