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. 2021 Feb 5;11:620716. doi: 10.3389/fimmu.2020.620716

Figure 1.

Figure 1

(A) Overview of cellular processes in the ABM. In an established GC a dark zone (DZ) and a light zone (LZ) are distinguished. CBs and CCs prefer to move in the direction of the CXCL12 and CXCL13 chemokines produced by the CRCs and FDCs respectively. Tfh cells prefer to move towards the LZ. FDCs carry Ag that can be captured by CCs. CCs may be positively selected through interaction with Tfh cells after which they can recycle to the dark. In the DZ the CB will (a)symmetrically divide. After cell division, an output cell is produced, or the cell differentiates to a CC. Cells die through apoptosis if they do not interact with the FDC and Tfh cells. (B) Schematic overview of the BcR and CD40 signaling events during the GC reaction. Durations t indicate non-fixed time intervals (cell states). At the end of each interval the concentrations of BCL6, IRF4, and BLIMP1 are updated using the differential equations. A CB (Ag−; blue cell) differentiates to a CC (Ag−; yellow cell) within a time duration t0. The CC interacts with the FDC for a time duration t1 during which BcR signaling occurs. Subsequently, CD40 signaling is active for duration t3 during B-cell – Tfh interaction. Successful interaction will result in an Ag+ cell. Asymmetric division occurs with a probability p=0.72. Differentiation of CB to a CC always initializes the CC to Ag−.