Specific and nonspecific imaging of localized Fisher Immunotype 1 Pseudomonas aeruginosa infection with radiolabeled monoclonal antibody

To determine if radiolabeled specific antibodies directed against bacterial antigens could be used to detect sites of infection, gamma camera imaging studies were performed in animals infected with Pseudomonas aeruginosa. Murine monoclonal antibodies (Mabs) directed against Fisher Immunotype 1 Pseudomonas aeruginosa and a nonmicrobial, nonmammalian haptene, p-arsinillic acid, were labeled with ¹²⁵I by the lodogen-Bead method. Unilateral, deep thigh infections were created by innoculation with 2 x 10⁸ Fisher Immunotype 1 P. aeruginosa. Twenty-four hours later, one of the radiolabeled antibodies was injected intravenously at a dose of 0.25 mg/kg (100-150 μCi). Serial gamma imaging was then carried out beginning at 4 hr and at ~24-hr intervals thereafter. Beginning as early as 4 hr postinjection, the area of inflammation could be visualized with either the specific or nonspecific Mab, with the images continuing to intensify until 24-48 hr postinjection. At 48 hr, the contrast between lesion and background with the nonspecific Mab began to fade, while the contrast in the specific Mab-generated images continued to intensify until ~192 hr postinjection. Clear-cut differentiation between specific and nonspecific Mab-generated images was possible by 72 hr postinjection. We conclude that specific immune imaging of localized infection with Mab's directed against specific microbial antigens is possible and should be clinically useful. In addition, images created by the localization of immunoglobulin non-specifically at the site of inflammation in the first 24-48 hr postinjection may also provide useful informations as to the anatomic location of hidden abscesses.