Fig. 4

Example of the use of a stochastic transition to model interaction among entities. The guard on the stochastic transition randomly selects only tokens that represent TH cells that are in the active state (th:1=“active”) and B cells that are in the presenting state (b:1=“presenting”). Moreover the activation of the transition is achieved only if both the cells have the same receptor specificity (b:4 = th:4). As a result of the activation of the transition we will obtain duplication of TH cells by giving back 2 identical TH cells to the TH place (2’th), a memory B cell with the same position and specificity, but with renewed life (1’(“memory”,b:2,10,b:4))) and, as a result of a asymetrical division, a new plasma cell (PB) with same receptor and characteristics of the progenitor B cells (1’(“plasma”,b:2,b:3,b:4))