Extended Data Fig. 8: Negative-stain electron microscopy analysis of H1 HA complexed with polyclonal antibody Fabs prepared from NHPs immunized with qsCocktail-I53_dn5 or qsMosaic-I53_dn5.

a, Negative-stain electron microscopy analysis of Fabs obtained from NHPs immunized with qsCocktail-I53_dn5 in complex with recombinant H1 MI15 HA trimers. Two-dimensional classifications were generated using 847,873 particles collected from 4,112 micrographs. The frequencies of complexes containing Fab fragments bound to RBD (81%), vestigial esterase (18%), or stem (1%) domains are presented as pie charts in Fig. 5c. b, Negative-stain electron microscopy analysis of Fabs obtained from NHPs immunized with qsMosaic-I53_dn5 in complex with recombinant H1 MI15 HA trimers. 2D classifications were generated using 997,557 particles collected from 3,237 micrographs. The frequencies of complexes containing Fab fragments bound to RBD (69%), vestigial esterase (24%), or stem (7%) domains are presented as pie charts in Fig. 5c. The top part of each panel shows representative reference-free 2D class averages. Scale bars, 20 nm. The bottom part of each panel shows seven representative 3D reconstructions of HA–Fab complexes. Single complexes containing Fabs of multiple specificities were counted once against each specificity. The coordinates of an H1 HA crystal structure (PDB 1RUZ) and a Fab fragment (PDB 3GBN) were fitted into the electron microscopy densities. Light blue ribbons, H1 HA; cyan or magenta ribbons, Fabs. All experiments were performed once.