Neutralizing antibodies derived from the B cells of 1918 influenza pandemic survivors.

This residue is located at the antigenic region Sb. Two epitope-specific mAbs (1F1 and 1I20) were tested for recognition of HA from a series of representative twentieth century H1N1 viruses. MAb 1F1 bound weakly to HA from A/Weiss/43 and A/USSR/92/77, while none recognized HA from A/FM/1/47 and A/New Caledonia/20/99. The residue at position 200 is Ser in all these virus isolates except for A/New Caledonia/20/99 where the epitope is conserved (P200). MAb 1I20 light chain isotype is kappa.