Spectral and fluorescence imaging of immune system and tissue response to an immunogenic agent

Abstract

Imaging of immune system and tissue response to immunogenic agents can be important to the development of new biomaterials. Additionally, quantitative functional imaging can be useful for testing and evaluation of methods to alter or control the immune system response to implanted materials. In this preliminary study, we employ spectral imaging and fluorescence imaging to measure immune system and tissue response to implanted immunogenic agents. Poly (D,L lactide-co-glycolide) (PLGA) with a 50:50 composition was used to create immunogenic microparticles (MPs). Lipopolysaccharide (LPS) encapsulated in the MPs was used to provoke a tissue immune response in mice and encapsulated fluorescein isothiocyanate (FITC) was used to fluorescently label the MPs for imaging. Control MPs did not contain LPS. The MPs were delivered at 50 particles/μL in a total volume of 20μL by subcutaneous injection in the skin of a nude mouse in a dorsal skin-fold window chamber preparation. Cultured immune cells from a mouse leukemic monocyte macrophage cell line were exogenously labeled with the fluorescent dye DiD in solution at a concentration of 8000cells/μL. Immediately after window chamber surgery and implantation of the MPs, 100μL of the fluorescent macrophage solution was administered via the tail vein. Fluorescence imaging was used to track MPs and macrophages while spectral imaging was used for imaging and measurement of hemoglobin saturation in the tissue microvasculature. Imaging was performed periodically over about three days. The spectral and fluorescence imaging combination enabled detailed observations of the macrophage response and functional effects on the tissue.