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.