Affinity-matured late GC B cells bind and neutralize heterologous influenza viruses. (A) Lineage tree of clonal family 05.89107.H1N1 from participant 05. IGHV and IGHJ gene use is indicated. Cells from which mAbs are derived are labeled with the cell of origin and the week isolated. Scale bar indicates mutations per codon. P value is calculated as described in the methods. (B) Optical density (OD) at 490 nm of A/Michigan/45/2015 H1-binding mAbs from clonal family 05.89107.H1N1. (C) Binding of Fabs from clonal family 05.89107.H1N1 to A/Michigan/45/2015 H1 as measured by BLI. K_D, dissociation constant. (D) Binding of mAbs from clonal family 05.89107.H1N1 to the indicated H1, H2, and H5 HA proteins as measured by ELISA. Scale bar is the area under the curve (AUC). (E) Minimum concentration of antibody required to neutralize the indicated viruses. CR9114 was used as a positive control. Each point represents one of two replicates. See also Fig. S3.