Depot Indocyanine green dye for in vivo visualization of infiltrating leukocytes

Abstract

We have developed a method to label and image myeloid cells infiltrating the mouse retina and choroid in vivo, using a single depot injection of Indocyanine green dye (ICG). This was demonstrated using different ocular mouse models of inflammation and angiogenesis – endotoxin-induced uveitis (EIU), experimental autoimmune uveoretinitis (EAU) and laser-induced choroidal neovascularisation (CNV). A near-infrared scanning laser ophthalmoscope was used for in vivo imaging of the eye and flow cytometry was used on blood and spleen to assess the number and phenotype of labelled cells. We found that in vivo intravenous administration failed to label any leukocytes, whereas depot injection, either intraperitoneal or subcutaneous, was successful in labelling CD11b+ myeloid cells. Progression of inflammation in the retina could be traced over a period of 14 days following a single depot injection of ICG. Additionally, flow cytometric analysis revealed that the predominant population of cells stained by ICG are circulating and splenic reservoir CD11b+ myeloid cells. The translation of this approach into clinical practice would enable visualisation of immune cells in situ. This will not only provide a greater understanding of pathogenesis, monitoring and assessment of therapy in many human ocular diseases but also open the ability to image immunity live for neurodegenerative disorders, cardiovascular disease and systemic immune mediated disorders.