[Materials and Methods] We incubated macrophages with PEI-coated SPIONs and measured IL-12 secretion into medium. Concomitantly, we studied the gene expression profile, activation markers, and mitogen-activated protein kinase (MAPK) pathway activation. To elucidate TLR4 (Toll-like receptor 4) and ROS (reactive oxygen species) involvement, we analyzed gene expression and p44/p42 MAPK phosphorylation in RAW264.7 mouse macrophages pretreated with CLI095 (a TLR4 inhibitor) or BHA (a ROS scavenger). We quantified podosomes in PEI-coated SPION-treated RAW264.7 cells and determined their capacity to degrade fluorescent-stained gelatin.

[Results] PEI-coated SPIONs induced phosphorylation of p38 MAPK, p44/p42 MAPK and JNK, and upregulated CD40, CD80, CD86 and I-A/I-E activation markers. PEI-coated SPION-induced macrophage activation depended partially on TLR4 and ROS signaling, and differed from that induced by lipopolysaccharide. PEI-coated SPIONs promoted podosome formation in murine macrophages, but inhibited gelatin degradation. This effect seems to be due to overexpression of genes related to metalloproteinase (MMP) inhibitors and to downmodulation of active MMP-2.

[Introduction] Considerable efforts have been made to develop multifunctional platforms for cancer gene therapy. One current strategy is the combination of SPIONs (superparamagnetic iron oxide nanoparticles) and polyethylenimine (PEI), due to their unique chemical and physical properties. PEI appears to activate different immune cells toward an inflammatory response (M1/TH1), whereas the nature of the SPION-induced response is unclear. Nonetheless, the immunoreactivity of PEI-coated SPIONs has not been addressed.

Poster presented at the 4th European Congress of Immunology, held in Vienna (Austria) on September 6-9th, 2015. Tuesday, September 8, 2015. P.C.12 Macrophages - Part 2.

[Conclusions] PEI-coated SPIONs induced an M1-like phenotype that was partially dependent on TLR4 and ROS, and modulated podosome dynamics.