The use of radiolabeled nonspecific immunoglobulin in the detection of focal inflammation.

The serendipitous discovery that radiolabeled nonspecific immunoglobulin G (IgG) accumulates at a site of focal inflammation has led to the development of a new radiopharmaceutical for inflammation scanning, 111In-IgG. This reagent has been extensively studied in humans with focal infection and has been shown to be both safe and effective. It has been especially useful in the evaluation of patients with possible abdominal and skeletal infection, with the ability to perform serial scans being an important attribute in terms of determining "proof of cure." Preliminary data suggest that this approach may be particularly useful in immuno-compromised patients and may find a role in the quantitative assessment of patients with such noninfectious inflammatory processes as rheumatoid arthritis and inflammatory bowel disease. A new method of labeling IgG with technetium, via the hydrazino nicotinamide derivative, holds promise in terms of substituting this more practical radionuclide for indium. However, caution must be directed against total substitution, because such processes as suspected vascular or skeletal prosthesis infection may require the longer half-life of 111In for satisfactory diagnosis. When one compares the results obtained with radiolabeled IgG against the ideal specifications for a radiopharmaceutical to be used for inflammation imaging, most of the requirements are met. The major weakness of this approach is that even with the technetium-labeled reagent, a minimum of 6 to 12 hours is necessary for a scan to become positive, which is not acceptable in the evaluation of acutely evolving processes. Development of other radiopharmaceuticals for this purpose remains to be accomplished.