In vivo targeting of activated leukocytes by a β₂-integrin binding peptide

Background: In immunopathological conditions, clinical diagnosis is commonly made on the basis of patient symptoms, measurement of blood leukocyte levels or proinflammatory biomarkers, non-specific radiological findings and, regarding infection, microbiological analysis. Nevertheless, frequently the exact spatial location of inflammation or even infection cannot be reliably identified, despite the use of up-to-date clinical, laboratory and imaging techniques. For this reason, new tools are warranted for use in advanced diagnosis and therapy targeting in patients. Objective: The peptide CPCFLLGCC (LLG), known to bind activated β₂-integrins in vitro, was fused with green fluorescent protein (GFP) to test the ability of LLG fusions to target and bind activated leukocytes in vivo. Methods: A murine skin scratch inflammation model was chosen for the convenient non-surgical detection of GFP. Results: The murine skin lesion inflammation model demonstrated in vivo targeting of LLG-GFP to sites of inflammation. Targeting by LLG-GFP fusion construct depends on the ability of the LLG-moiety to bind activated leukocytes. Control construct unable to bind β₂-integrins appeared biologically inert. Conclusion: The data support the possibility of using this fluorescently labeled peptide as a tool for both the detection of and targeting to inflammatory sites characterized by robust leukocyte activation.