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 chemo tactic peptides and interleukins for imaging of infection and inflamma tion. In the present study, the potential of two species of interleuki n 1 (IL-1), IL-1 alpha and IL-1 beta, 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 o f infection. TL-la, IL-1 beta, IL-1ra and fMLFK were labelled with iod ine-123 according to the Bolton-Hunter method. Twenty-four hours after induction of Escherichia coli abscesses in the left thigh muscle, rab bits were injected intravenously with 0.5 mCi of I-123-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 rapidl y cleared from the blood, at 20 h p.i. blood levels and the levels in most organs of I-123-fMLFK were significantly lower than those of the other three agents (P < 0.05). The abscesses were clearly visualized w ith all agents from 4 h p.i. onwards. After 1 h p.i., the abscess upta ke of I-123-IL-1 beta 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 muscl e ratios were obtained with I-123-IL-1 beta, i.e. 39.0 +/- 11.5 vs 18. 7 +/- 5.4, 18.1 +/- 2.3 and 29.9 +/- 7.0 for I-123-IL-1 alpha, I-123-I L-1ra and I-123-fMLFK, respectively. In conclusion, all agents localiz ed in the infectious focus. The potential of radiolabelled IL-1 beta f or imaging of infection was better than that of the other agents: high er absolute uptake in the infection and high er abscess-to-contralater al muscle ratios were obtained. The observation of localization of rad iolabelled IL-1ra in infection was important since this protein can be administered to humans without any side-effects.