Figure 2.

Nature of the “long-lived” germinal center (GC) response. A response in which GCs are observable several months after induction could result from different GC formation and disappearance kinetics. The figure illustrates three possible models. (A) Long-lived GCs: Individual GCs appear simultaneously close to the induction of the response and last until the GC reactions resolve several months later. Somatic hypermutation (SHM) load increases and clonal diversity decreases continuously as the reaction progresses. (B) Recurrent GCs: Individual GCs are short-lived, but as a GC disappears, a new one appears in the same follicle but with a different clonal composition, and possibly lower SHM load. (C) Long-lived GCs as in A are constantly being seeded by B-cell clones recruited from the outside, either from the memory or naïve pools. Diversity remains high throughout the course of the response. Importantly, cross-sectional analysis at a given time point does not allow for a clear distinction between these models.