We performed adoptive transfer experiments with KL25HL-AIDrep B cells on day 20 after infection and sorted GL7+ GC B cell progeny on day 35, as outlined in Figure 4A. We determined both intronic sequences downstream of JH as a readout of overall AID activity in the transferred KL25HL-AIDrep B cells and also KL25 VH sequences as an indicator of affinity maturation. Here, AICDA is linked to infection.