Clonal Selection: How the Adaptive Immune System Picks a Fighter (2D)

Timeline

Simulation speed 1.0×

Repertoire diversity 48 clones/pool

Affinity threshold 0.62

A dendritic cell is about to present a pathogen fragment. Each dot below is one lymphocyte clone with its own receptor shape and colour — only clones whose receptor fits the antigen will respond.

Live Readout

Model hour

0.0

Phase

Presentation

T-clone(s) matched

0 / 0

B-clone(s) matched

0 / 0

Winning T population

Winning B / plasma

How it works

The body carries a huge, pre-existing repertoire of T-cell and B-cell clones, each with a slightly different, randomly-generated receptor shape. No single clone is built to fight every pathogen — instead, whichever clone's receptor happens to fit the invader is selected.

Antigen presentation — a dendritic cell (antigen-presenting cell) breaks the pathogen down and displays one fragment on its surface.
Clonal selection — every T-cell clone in the repertoire is screened for receptor affinity to that fragment. Only clones above the affinity threshold respond; higher-affinity clones expand faster.
T-cell clonal expansion — the winning T-cell clone divides repeatedly (logistic growth, not a fixed rate), turning a handful of specific cells into a large army in days.
T-cell help → B-cell activation — once enough helper T-cells exist, they hand off activation signals to the B-cell clone whose receptor also fits the same antigen.
B-cell expansion & differentiation — the matched B-cell clone proliferates and differentiates into antibody-secreting plasma cells, then the response contracts, leaving a small pool of long-lived memory cells behind.

Presentation

Matched, expanding clone Non-matching clone (dormant) Antigen / plasma output