Akiyoshi Hoshino

Nanocrystal quantum dots (QDs) have been applied to molecular biology because of their greater and longer fluorescence. Here we report the potential cytotoxicity of our characterized QDs modified with various molecules. Surface modification of QDs changed their physicochemical properties. In addition, the cytotoxicity of QDs was dependent on their surface molecules. These results suggested that the properties of QDs are not related to those of QD-core materials but to molecules covering the surface of QDs.

Strong photoluminescence in the blue region of the visible spectrum was observed for a dispersion of allylamine-capped silicon quantum dots in water. Their ease of synthesis and optical properties make them excellent candidates for biomedical applications, as demonstrated by their incorporation inside the cytosol of HeLa cells (see microscopy image, the inset shows the fluorescence from the silicon quantum dots on excitation with UV light).

Quantum dots (QDs) such as CdSe QDs have been introduced as new fluorophores. The QDs conjugated with antibody are starting to be widely used for immunostaining. However there is still not sufficient analysis of the toxicity of QDs in the literature. Therefore we evaluated the cell damage caused by the quantum dots for biological applications. We performed cell viability assay to determine the difference in cell damage depending on the sizes and colors of mercapto-undecanoic acid (MUA) QDs and the cell types. The results showed that the cell viability decreased with increasing concentration of MUA-QDs. But in the case of Vero cell (African green monkey's kidney cell) with red fluorescence QD (QD640), the cell damage was less than for the others. Furthermore through the flow cytometry assay we found that this cell damage caused by MUA-QD turned out to be cell death after 4-6-hr incubation. From the two assays described above, we found that there is a range of concentration of MUA-QDs where the cell viability decreased without cell death occurring and thus we conclude that attention should be given when MUAQDs are applied to living organisms even in low concentrations.

Dectin 1 is a mammalian cell surface receptor for (1-->3)-beta-d-glucans. Since (1-->3)-beta-d-glucans are commonly present on fungal cell walls, it has been suggested that dectin 1 is important for recognizing fungal invasion. In this study we tried to deduce the amino acid residues in dectin 1 responsible for beta-glucan recognition. HEK293 cells transfected with mouse dectin 1 cDNA could bind to a gel-forming (1-->3)-beta-d-glucan, schizophyllan (SPG). The binding of SPG to a dectin 1 transfectant was inhibited by pretreatment with other beta-glucans having a (1-->3)-beta-d-glucosyl linkage but not by pretreatment with alpha-glucans. Dectin 1 has a carbohydrate recognition domain (CRD) consisting of six cysteine residues that are highly conserved in C-type lectins. We prepared 32 point mutants with mutations in the CRD and analyzed their binding to SPG. Mutations at Trp(221) and His(223) resulted in decreased binding to beta-glucan. Monoclonal antibody 4B2, a dectin- 1 monoclonal antibody which had a blocking effect on the beta-glucan interaction, completely failed to bind the dectin-1 mutant W221A. A mutant with mutations in Trp(221) and His(223) did not have a collaborative effect on Toll-like receptor 2-mediated cellular activation in response to zymosan. These amino acid residues are distinct from residues in other sugar-recognizing peptide sequences of typical C-type lectins. These results suggest that the amino acid sequence W221-I222-H223 is critical for formation of a beta-glucan binding site in the CRD of dectin 1.