A laboratory measures antibody affinity maturation in germinal centres. The process that selects B cells with progressively higher affinity antibodies after somatic hypermutation involves competition for which limiting resource?
- A IL-2 from follicular dendritic cells
- B CD28 co-stimulatory signals from plasmablasts
- C Antigen presented on follicular dendritic cells (FDC) ✓
- D T-cell receptor diversity from naive T cells
Explanation
During the germinal centre reaction, centrocytes (B cells that have undergone somatic hypermutation) compete for limiting antigen displayed on follicular dendritic cells. Only B cells with high-affinity BCR can capture sufficient antigen and present it to follicular helper T cells (Tfh) to receive CD40L and IL-21 survival signals; low-affinity variants die by apoptosis. This selection process drives progressive affinity maturation, culminating in memory B cells and long-lived plasma cells. IL-2 is primarily a T-cell growth factor, and CD28 is expressed on T cells, not B cells at this stage.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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