Sourav P. Mukherjee

Graphene and the Immune System: A Romance of Many Dimensions

Graphene-based materials (GBMs) are emerging as attractive materials for biomedical applications. Understanding how these materials are perceived by and interact with the immune system is of fundamental importance. Phagocytosis is a major mechanism deployed by the immune system to remove pathogens, particles, and cellular debris. Here, we discuss recent studies on the interactions of GBMs with different phagocytic cells, including macrophages, neutrophils, and dendritic cells. The importance of assessing GBMs for endotoxin contamination is discussed as this may skew results. We also explore the role of the bio-corona for interactions of GBMs with immune cells. Finally, we highlight recent evidence for direct plasma membrane interactions of GBMs.

Structural dependence of in vitro cytotoxicity, oxidative stress and uptake mechanisms of poly(propylene imine) dendritic nanoparticles.

The in vitro cytotoxic and intracellular oxidative stress responses to exposure to poly(propylene imine) (PPI) dendritic nanoparticles of increasing generation (number of repeated branching cycles) (G0–G4) were assessed in an immortal non‐cancerous human keratinocyte cell line (HaCaT). Confocal fluorescence microscopy with organelle staining was used to explore the uptake and intracellular trafficking mechanisms. A generation‐ and dose‐dependent cytotoxic response was observed, increasing according to generation and, therefore, number of surface amino groups. A comparison of the cytotoxic response of G4 PPI and the related G4 poly(amido amine) dendrimer indicates that the PPI with the same number of surface amino groups elicits a significantly higher cytotoxic response. The trend of cytotoxicity versus dendrimer generation and, therefore, size is discontinuous in the region of G2, however, indicating a difference in uptake mechanism for higher compared to lower generations. Whereas the higher generations elicit an oxidative stress response at short exposure times, the lower generations indicate an antioxidant response. Confocal microscopy indicates that, whereas they are prominent at early exposure times for the larger PPI dendrimers, no evidence of early stage endosomes was observed for lower generations of PPI. The results are consistent with an alternative uptake mechanism of physical diffusion across the semipermeable cell membrane for the lower generation dendrimers and are discussed in terms of their implications for predictive models for nanotoxicology and design strategies for nanomedical applications. Copyright

Macrophage sensing of single-walled carbon nanotubes via Toll-like receptors

Carbon-based nanomaterials including carbon nanotubes (CNTs) have been shown to trigger inflammation. However, how these materials are ‘sensed’ by immune cells is not known. Here we compared the effects of two carbon-based nanomaterials, single-walled CNTs (SWCNTs) and graphene oxide (GO), on primary human monocyte-derived macrophages. Genome-wide transcriptomics assessment was performed at sub-cytotoxic doses. Pathway analysis of the microarray data revealed pronounced effects on chemokine-encoding genes in macrophages exposed to SWCNTs, but not in response to GO, and these results were validated by multiplex array-based cytokine and chemokine profiling. Conditioned medium from SWCNT-exposed cells acted as a chemoattractant for dendritic cells. Chemokine secretion was reduced upon inhibition of NF-κB, as predicted by upstream regulator analysis of the transcriptomics data, and Toll-like receptors (TLRs) and their adaptor molecule, MyD88 were shown to be important for CCL5 secretion. Moreover, a specific role for TLR2/4 was confirmed by using reporter cell lines. Computational studies to elucidate how SWCNTs may interact with TLR4 in the absence of a protein corona suggested that binding is guided mainly by hydrophobic interactions. Taken together, these results imply that CNTs may be ‘sensed’ as pathogens by immune cells.