Quantum dots decorated with pathogen associated molecular patterns as fluorescent synthetic pathogen models

Abstract

We attached the pathogen associated molecular pattern Kdo(2)-Lipid A (the lipopolysaccharide (LPS) from Escherichia coli (E. coli)) to QDs by hydrophobic interactions to synthetically mimic the surface of E. coli. QD-LPS conjugates bind, are taken up and activate effectively macrophages in vitro and they have potent immunostimulatory activity in vivo.

Fig. 1

Analogy between E. coli and LPS (Kdo₂-lipid A)-coated QDs.

Fig. 2

(A) Confocal images of J774 macrophages after staining with Hoechst 33343 (blue, nuclei) and DiOC18 (green, membrane) at 5 min, 35 min, and 65 min after beginning incubation with 10 nM QD-LPS (red) containing medium at 37 °C (top). The 3D reconstituted images the cell marked with an arrow (bottom). (B) Flow cytometry analysis of macrophages before (black) and after incubation with QD-LPS (0.65 nM, red line; 65 pM, blue line).

Fig. 3

(A) IL-6 release from macrophages treated at 1/10 dilution with: [QD-LPS] = 1.5 nM; [LPS] = 250 nM; [control QD] = 2.5 nM. PMB is the LPS inhibitor polymyxin B; [PMB] = 250 μM. PBS = phosphate-buffered saline, pH 7.4. The control QD is coated with PC and PEG-PE. Incubation time = 16 h. (B) IL-6 release from bone-marrow derived dendritic cells from wild-type mice treated at 1/10 dilution with: [QD-LPS] = 1.5 nM; [LPS] = 250 nM; [control QD] = 2.5 nM. PMB is the LPS inhibitor polymyxin B; [PMB] = 250 μM. PBS = phosphate-buffered saline, pH 7.4. The control QD is coated with PC and PEG-PE. Incubation time = 24 h

Fig. 4

(A) Antibody (Ab) responses (total Ab, IgG1 and IgG2c) to antigen (DNP-OVA, 100 μg) alone and co-administered (i.p.) with QD-LPS (10 pmol), LPS (4 μg) and E. coli LPS (10 μg) emulsified in IFA (s.c. injected); boosting with DNP-OVA after 56 days. Values plotted are means based on titers from five individual mice and representative of two different experiments.