Imaging of infection in rabbits with radioiodinated interleukin-1 (α and β), its receptor antagonist and a chemotactic peptide: a comparative study

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Abstract
Previous studies have reported the favourable characteristics of chemotactic peptides and interleukins for imaging of infection and inflammation. In the present study, the potential of two species of interleukin 1 (IL-1), IL-1α and IL-1β, the IL-1 receptor antagonist (IL-1ra) and the synthetic chemotactic peptide N-formyl-methionyl-leucyl-phenylalanyl-lysine (fMLFK) were directly compared in a rabbit model of infection. IL-1α, IL-1β, IL-1ra and fMLFK were labelled with iodine-123 according to the Bolton-Hunter method. Twenty-four hours after induction of Escherichia coli abscesses in the left thigh muscle, rabbits were injected intravenously with 0.5 mCi of 123I-labelled agent. Gamma camera images were obtained at 5 min and 1, 4, 8 and 20 h p.i. Biodistribution was determined at 20 h p.i. Although all agents rapidly cleared from the blood, at 20 h p.i. blood levels and the levels in most organs of 123I-fMLFK were significantly lower than those of the other three agents (P123I-IL-1β was significantly higher than that of the other agents (P123I-IL-1β, i.e. 39.0±11.5 vs 18.7±5.4, 18.1±2.3 and 29.9±7.0 for 123I-IL-1α, 123I-IL-1ra and 123I-fMLFK, respectively. In conclusion, all agents localized in the infectious focus. The potential of radiolabelled IL-1β for imaging of infection was better than that of the other agents: higher absolute uptake in the infection and higher abscess-to-contralateral muscle ratios were obtained. The observation of localization of radiolabelled IL-1ra in infection was important since this protein can be administered to humans without any side-effects.

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