Clonal diversity by asymmetry

When challenged by an intruder, the immune system generates a bewildering array of different T lymphocyte subsets. Cells in functionally distinct subsets somehow share specificity for an identical antigen. A mechanism for generating this clonal diversity is now explained by John Chang, Vikram Palanivel, Steven Reiner (University of Pennsylvania, Philadelphia, PA), and colleagues.

The subsets, say the researchers, arise from the first, asymmetric division that a naive T cell makes after being stimulated by antigen. The source of the asymmetry is the immune synapse—the connection of the naive T cell to the antigen-presenting cell (APC) that is stimulating it. As the T cell divides, the synapse-proximal T cell becomes an effector cell responsible for immediate fighting, whereas the synapse-distal cell becomes a memory T cell.

The model stands...