Imaging infections with antibodies: A quantitative autoradiographic analysis

Radiolabeled IgG has recently been demonstrated to effectively image infections. A potential but unproven mechanism for this localization is the specific binding of IgG to Fc receptors on the surface of inflammatory cells in infections. In an animal model of soft tissue infection, quantitative autoradiography was used to measure 125I-labeled IgG and albumin in tissues with a spatial resolution sufficient to associate these proteins with cellular morphology. Gamma camera images at 24 h localized the infection with target-to-background ratios of 2.2 ± 0.5 for IgG and 2.3 ± 1.0 for albumin (mean ± SD). Using quantitative autoradiography at 1 h post-injection, significantly higher concentrations were found in infected thighs of 2–4% of initial plasma concentrations (CPo) as compared to 0.2–0.3% of CPo in noninfected thighs (P < 0.05); at 24 h post-injection, higher concentrations (7–8% of CPo) were found in infected thighs. Radiolabeled proteins were not inflammatory cell associated and were localized primarily within the edematous interstital spaces of the infection.