Irf4 is induced in response to CD40L signals, transduced by the node NF-kappaB. Irf4 regulates its own activation and is positively regulated by Blimp1 if its inhibitor Bcl6 is off.

Activation of the IL-2R receptor by IL-2 induces STAT5 activation.

Activation of the CD40 receptor promotes the activation of the transcription factor NF-$\\kappa$B in response to CD40L stimulation.

The CD40 node is activated by the input node CD40L simulating the direct contact of B with T cells mediated by the union of the CD40 receptor with its ligand CD40L.

AID node is positively regulated by the presence of Pax5 in response to CD40 and IL-4 signals, transduced by NF-kappaB and STAT6 respectively. AID is active only if its inhibitor Blimp1 is absent.

XBP1 is activated by Blimp1 if the suppressor Pax5 is absent.

BCR is activated and translocated by the presence of extracellular antigen inducing a intracellular signaling response

The IL-21R receptor is induced by IL-21, a signal required for differentiation toward plasma cells.

The IL-2R node is induced by the input node IL-2, simulating the activation of the IL-2R receptor by IL-2 stimulation, a signal involved in differentiation of germinal center B cells.

The IL-4 input node induces the IL-4R node simulating the activation of the IL-4R receptor activation by the cytokine IL-4 required for GC differentiation.

Pax5 is maintained active by low levels of Irf4 and possibly by a positive regulatory circuit with Ebf1 that plays a key role during early B cell differentiation, included as a positive autoregulatory interaction. Pax5 is inhibited if Blimp1 or ERK are present.

Activation of the IL-4R receptor induces STAT6 in response to IL-4 stimulation.

BCR cross-linking promotes ERK activation after Ag stimulation.

IL-21 signals are transduced by STAT3, represented in the model as a positive interaction of the IL-21R receptor with STAT3.

The node Bcl6 is induced in response to IL-2 and IL-4, transduced by STAT5 and STAT6 respectively. Its activation depends on the presence of Pax5, and on the mechanisms maintaining its own expression. Bcl6 node is repressed if either the nodes Blimp1, Irf4 or ERK are active.

Blimp1 is activated by Irf4 if all its inhibitors, Pax5, Bcl6 and Bach2 are inactive. Blimp1 is induced by Ag and IL-21 which are transduced by ERK and STAT3, respectively.

Bach2 node is activated if its positive regulator Pax5 is active and the suppressor Blimp1 is absent.