Papillomavirus virus-like particles induce cytokines characteristic of innate immune responses in plasmacytoid dendritic cells

Human papillomavirus (HPV) virus-like particles (VLP) are being extensively tested as vaccines for the prevention of HPV-associated cervical cancer. Dendritic cells (DC) acquire and present antigens, initiating innate and adaptive immune responses. It has been shown previously that DC of the myeloid lineage are capable of generating adaptive immune responses to HPVVLP in vitro. However, the capacity of plasmacytoid DC (pDC) to acquire HPV VLP and the nature of the immune response generated have not been reported. In this study we found that freshly isolated as well as CpG-matured pDC bind papillomavirus VLP and that internalization occurs preferentially in the immature pDC. In contrast to myeloid DC, pDC did not undergo phenotypic maturation upon exposure to HPV16 VLP. However, HPV16 VLP induced pDC to secrete of IFN-alpha and IL-6, both cytokines that play a role in the generation of antibody responses, as well as TNF alpha and IL-8. Given that VLP do not contain viral nucleic acids, these results indicate that viral capsids alone may be capable of inducing cytokine production by pDC. Finally, CpG-activated pDC, but not pDC exposed to HPV16 VLP, activated lymphocytes to secrete IL-10 and low levels of IFN-gamma. Together these findings suggest a possible immunogenic effect of pDC in the setting of VLP vaccination.