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

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-1alpha and IL-1beta, 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-1alpha, IL-1beta, 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 (P<0.05). The abscesses were clearly visualized with all agents from 4 h p.i. onwards. After 1 h p.i., the abscess uptake of 123I-IL-1beta was significantly higher than that of the other agents (P<0.05), with the highest uptake observed at 8 h p.i. (1.3%+/-0.3%). After 20 h p.i., the highest abscess-to-contralateral muscle ratios were obtained with 123I-IL-1beta, i.e. 39.0+/-11.5 vs 18.7+/-5.4, 18.1+/-2.3 and 29. 9+/-7.0 for 123I-IL-1alpha, 123I-IL-1ra and 123I-fMLFK, respectively. In conclusion, all agents localized in the infectious focus. The potential of radiolabelled IL-1beta 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.