Syntheses of fluorescent imidazoquinoline conjugates as probes of Toll-like receptor 7

Toll-like receptor (TLR)-7 agonists show prominent immunostimulatory activities. The synthesis of a TLR7-active N¹-(4-aminomethyl)benzyl substituted imidazoquinoline 5d served as a convenient precursor for the covalent attachment of fluorophores without significant loss of activity. Fluorescence microscopy experiments show that the fluorescent analogues are internalized and distributed in the endosomal compartment. Flow cytometry experiments using whole human blood show differential partitioning into B, T, and natural killer (NK) lymphocytic subsets, which correlate with the degree of activation in these subsets. These fluorescently-labeled imidazoquinolines will likely be useful in examining the trafficking of TLR7 in immunological synapses.