Fig. 2.

Hysteretic behavior of IRF4 for different values of β. The blue line shows the evolutionary steady states reached by a cell stimulated through the CD40 pathway. (A and B) After the signaling process is over, the cell reverts back to the initial GC steady state. (C) Above a critical ratio of production and degradation of IRF4, the GC state is no longer accessible and the GC B cells differentiate into a plasma cell. Therefore, the differentiation process has become a terminal, irreversible event.