Biologic effects of nanoparticle-allergen conjugates: time-resolved uptake using an in vitro lung epithelial co-culture model of A549 and THP-1 cells

Abstract

Nanotechnology is a fast growing field and already a multi-billion dollar market with numerous products available for consumers. TiO₂ and SiO₂ are by mass the most produced nanomaterials and, thus, of particular interest regarding their biological effects upon inhalation – especially in combination with other inhalable biomolecules such as allergens. We investigated the protein-binding capacity of these two nanomaterials and present detailed uptake profiles of protein-conjugated TiO₂ or SiO₂ nanoparticles (NPs) in A549 lung epithelial and THP-1 macrophage-like cells. TiO₂ and SiO₂ NPs (both with a hydrodynamic diameter of about 150 nm) are able to bind bovine serum albumin (BSA), green fluorescent protein (GFP) and the major birch pollen allergen Bet v 1 in substantial amounts that suggest protein monolayers around the particles. GFP-conjugated TiO₂ and SiO₂ NPs were taken up in A549 and THP-1 cells in a time-dependent manner as demonstrated by confocal laser scanning microscopy, flow cytometry and life cell imaging. By the aid of fluorescent proteins (GFP or fluorescently labeled Bet v 1) we found that both, the NPs and the conjugated proteins entered the cells. Using A549/THP-1 co-cultures, we showed that the majority of SiO₂ NPs is taken up by THP-1 cells; however, also A549 cells take up significant amounts of particles when co-cultured with THP-1 macrophage-like cells. The here discussed data provide valuable insights into protein (allergen) delivery by NPs at the lung epithelial barrier.