Gardasil-immunized sera or IgG possesses strong extracellular neutralization.
FcRn expressed on primary human keratinocytes (PHKs) mediates the uptake of IgG.
Bound or intracellular Gardasil-immunized IgG does not neutralize HPV virions.
Neutralization window of the immune sera is limited to 4 h in early passage PHKs.
Growth characteristics of PHKs affect the neutralization window from 4 h to 16 h.