Localization of abscess with an iodinated synthetic chemotactic peptide

N-formyl Nle-Leu-Phe-Nle-Tyr-Lys is a potent synthetic chemotactic peptide (CP), which binds to chemotactic receptors of neutrophils with high affinity. Because the peptide contains a tyrosine moiety, it can be readily labeled with a radioactive iodine. In this study, we investigated the possibility of abscess localization by i.v. administration of this radioiodinated CP. The peptide was iodinated with 125I using chloramine-T and purified using Bio-Gel P-2 chromatography. The final preparation had a purity of 88.5 +/- 3.8% (n = 6) and a specific radioactivity of 600-800 ci/mM. The iodinated CP bound to rabbit neutrophils specifically; its binding could be prevented by non-labeled CP. When 4-6 ng of 125-I-CP per kg body weight was injected into abscess-bearing rabbits, there was an immediate, but transient neutropenia, followed by a rebound neutrophilia. The abscess to muscle (A/M) ratio was 11.6 +/- 1.1 at 6 hrs and 11.0 +/- 4.7 at 24 hrs after injection; while the abscess to blood (A/B) ratio was 0.9 +/- 0.2 and 3.7 +/- 0.6 at 6 and 24 hrs post injection, respectively. Control animals injected with Na125I revealed an A/M ratio of 2.9 +/- 0.2 and an A/B ratio of 0.9 +/- 0.3 at 6 hrs after injection. Analysis of the radioactivity in the blood after 125I-CP administration, revealed that the majority (less than 87%) of the radioactivity was present as 125I-CP in the plasma fraction. Our results suggest that radioiodinated synthetic CP shows promise for abscess localization. However, further refinement of the method is required.