Plastic Surgery Research Council
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IMAGING WITH INDOCYANINE GREEN-LOADED MONOCYTES FOR DIFFERENTIATION OF CUTANEOUS INFLAMMATORY STATES IN A MOUSE MODEL
Presenter: Joani M Christensen, BA
Co-Authors: Chen Y; Brat GA; Buretta KJ; Cooney DS; Brandacher G; Johnson KE; Lee WP; Li X; Sacks JM
Johns Hopkins School of Medicine

Distinguishing normal postoperative inflammation from infectious processes can be challenging, and relies largely upon interpretation of clinical parameters and microbiologic data. An imaging modality that assesses variations in leukocytic infiltration could provide more specific information without the delays inherent in culture. Autologous monocytes loaded with the only FDA-approved near infrared fluorophore, indocyanine green (ICG), may be injected intravenously and homing assessed non-invasively using a clinically-applicable near infrared laser to investigate cutaneous inflammatory processes. RAW 264.7 mouse monocytes were coincubated with ICG solution. Fluorescence was confirmed microscopically. Homing ability of loaded cells was assessed in vitro using a microplate chemotaxis assay. Labeled cells were injected systemically into mice with induced sterile inflammation (Complete Freund s Adjuvant inoculation) or infection (Group A Streptococcus inoculation) of the hind limb. Whole animal near infrared imaging was completed using a near-infrared laser. Fresh frozen tissue from the area of inoculation was examined microscopically for fluorescence. Loaded cells were highly fluorescent in the near infrared range. In vitro, loaded cells retained ability to chemotax toward monocyte chemotactic protein-1 (p < 0.01). Following intravascular injection of loaded cells, whole animal imaging revealed local fluorescence at the inoculation site, with significantly different fluorescence ratios in the infection and inflammation model as early as 2 hours after injection (p<0.01) and the difference becoming more pronounced as time progressed. Microscopic examination of locally inflamed tissue revealed punctate areas of fluorescence, consistent with the presence of ICG-loaded cells. Whole animal near infrared imaging following systemic injection of indocyanine green-loaded monocytes can distinguish cutaneous infection from sterile inflammation. Development of a minimally invasive technique to rapidly image inflammation may lead to new tools to distinguish infectious from sterile inflammatory conditions at the bedside.


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