Detecting and differentiating microbes by dendritic cells for the development of cell-based biosensors

Dendritic cells (DCs) are a specialized family of antigen presenting cells. They play critical roles in sensing and processing microbial information through a series of pattern recognition receptors (PPRs), including the well-characterized toll-like receptors (TLRs). In this study, we demonstrated the utilization of a DC cell line, DC2.4, as a cell source for the detection and differentiation of microbes towards the development of cell-based biosensors. As a proof of principle, the gram-negative bacteria Escherichia coli K12 strain D21 and its lipopolysaccharide (LPS) mutants were used as model targets. The stimulation of DCs by bacterial strains was monitored by the production of nitric oxide (NO), and the colorimetric Greiss assay was used to quantify the level of NO produced. Our results demonstrated that DCs could detect and differentiate microbes with subtle differences in the composition of specific cell surface components, i.e. LPS, within minutes. Though the current colorimetric-based NO assay limited the detection sensitivity, we showed that DCs were able to detect as low as 2-3 bacteria per cell. Furthermore, compared to macrophages, DCs were superior in discriminating LPS mutants. Our study demonstrates that DCs possess great potential as cell sources for the development of novel cell-based biosensors for detecting microbes with high selectivity and sensitivity and rapid responsiveness. In addition, when DCs are coupled with other biosensor platforms, higher sensitivity can be expected.