Nanoparticles modify dendritic cell homeostasis and induce non-specific effects on immunity to malaria.

BACKGROUND: Many current vaccines to a specific pathogen influence responses to other pathogens in a process called heterologous immunity. We propose that their particulate nature contributes to non-specific effects. Herein, we demonstrate polystyrene nanoparticles modulate dendritic cell (DC) homeostasis, thereby promoting a persistent enhanced state of immune readiness to a subsequent infectious challenge.

METHODS: Particles (approximately 40 nm and 500 nm carboxylated polystyrene nanoparticles; PSNPs) alone or conjugated to a model antigen were injected in mice, and DCs in draining lymph nodes (dLNs) and bone-marrow (BM) quantified by flow cytometry. BM cells were tested for capacity to generate DCs upon culture with granulocyte and macrophage colony stimulating factor. Mice were challenged with Plasmodium yoelli. Blood parasitaemias were monitored by GIEMSA. Sera was analyzed for antibodies by ELISA.

RESULTS: Intradermal administration of 40 nm PSNPs induced anti-inflammatory cytokines, chemokines and growth factors, increased numbers and proportions of DCs in the dLN, and increased the capacity of BM to generate DCs. Consistent with these unexpected changes, 40 nm PSNPs pre-injected mice had enhanced ability to generate immunity to a subsequent malarial infection.

CONCLUSIONS: Intradermal administration of 40 nm PSNPs modifies DC homeostasis, which may at least in part explain the observed beneficial heterologous effects of current particulate vaccines. Further nanotechnological developments may exploit such strategies to promote beneficial non-specific effects.