Comparison of 99Tcm-labelled monoclonal anti-granulocyte antibody and 111In-labelled IgG for the detection of focal sites of infection in rats

Comparison of Animal Models with Soft Tissue Infection by Different Bacilli

In clinical medicine improved diagnostic methods for the detection of infection are needed. A good infectious animal model is very important for the development of a new diagnostic method or drug. The purpose of this study was to establish a good animal model with soft tissue infection. Twenty-four SD rats were divided into four groups (6 in each group). Various bacilli including Staphylococcus aureus (S. aureus), Streptococcus pneumoniae (S. pneumoniae), and Escherichia coli (E. coli) were injected intramuscularly into the left caudal thighs of three groups of rats to create soft tissue infection. In addition, normal saline was injected into the left caudal thighs of ten rats which were used as controls. Before and 48 hr after inoculation of the bacilli, a blood sample (0.5 ml) was taken from each rat and analyzed to determine the white blood cell count and differentiated cell count. In addition, 48 hr after the inoculation, 0.2 mCi of gallium-67 was injected via the tail vein. Gallium scan was performed at 24 hr and 48 hr after administration of the radiotracer. The dorsal view of both hind legs was imaged and analyzed by computers to calculate the lesion-to-normal (L/N) ratio. After imaging, all rats were sacrificed and specimens from portions of the infected thigh muscle were sent for histopathologic investigation to confirm the infection. The increase in both the WBC counts and the segmented polymorphonuclear leukocytes (PMNs) were most significant in the S. aureus group, followed by the S. pneumoniae group, E. coli group and normal control groups. The rats with S. aureus infection had significant gallium uptake at the site of infection and the highest L/N ratio of 2.14 on the 24-hr image and 2.0 on the 48-hr image. The rats with S. pneumoniae had the second highest L/N ratio (1.41 at 24 hr, and 1.48 at 48 hr). The L/N ratio for the E. coli group was 1.27 at 24 hr and 1.35 at 48 hr. No obviously abnormal gallium uptake was demonstrated in the normal controls. We conclude that all three bacilli induced a soft tissue infection in SD rats. S. aureus resulted in the most significant infectious signs.

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.

The use of monoclonal antibodies and antibody fragments in the imaging of infectious lesions

The advantage of immunoscintigraphy over autologous leukocyte techniques in the imaging of infection is the simplicity of its use compared with techniques that require the isolation of autologous white blood cells. The advantage over 99mTc- or 111In-labeled nonspecific human immunoglobulin is the excellent target-to-background ratio, which results from an endogenous background subtraction with the whole antigranulocyte antibody (99mTc-anti-NCA-95; BW250/183) and a rapid clearance of the antibody using an antigranulocyte Fab'-fragment (99mTc-anti-NCA-90; IMMU-MN3). The whole antibody is helpful for imaging of soft tissue infections, peripheral bone, and abdominal infections. Problems may arise occasionally in regions with normal bone marrow that are caused by human antimouse antibody (HAMA) formation. An infection or the entire extent of inflammation can be proven or excluded only at 24 hours postinjection. In contrast, antigranulocyte Fab'-fragment may have its advantage in an earlier localization of infectious lesions (1 hour) owing to its smaller molecular size and its lower affinity for its epitope. This may be promising in the detection of spinal infections and in infections in regions with the presence of normal bone marrow. Also advantageous is the negligible HAMA response rate. Problems may arise in abdominal infections because of an intestinal excretion of activity as early as 4 hours postinjection in some cases but more usually at 24 hours.

[Role of isotopic imaging in intensive care]

The real place of isotopic imaging in intensive care patients remains still unclear. This review aimed to consider the indications of isotopic imaging for improved diagnosis and therapy and to specify its place among the other techniques of exploration. Pulmonary perfusion and ventilation scintigraphies are valuable for the diagnosis of pulmonary embolism (PE). A "high probability" scintigraphy of the lungs ascertains the diagnosis of PE and allows to start a specific treatment without requiring a pulmonary angiography. This is not the case in the presence of a history of previous PE or if the arguments for a PE are only weak. A normal lung scintigraphy eliminates the diagnosis of a clinically significant PE all the more as an exploration of good quality of the lower limb veins remains negative. In the opposite a "non diagnostic" scintigraphy justifies a pulmonary angiography in intensive care patients. The diagnosis of myocardial contusion is made uneasy as the clinical symptoms, the ECG, the cardiac enzymes and the chest X-ray are only of limited value. Isotopic explorations of the heart could provide additional valuable data or be an alternative for 2 D echocardiography. The comparison of CPK-MB concentrations with a myocardial scintigraphy using thallium 201 is given as being very reliable, with positive and negative predictive values higher than 80%. An exploration restricted to the cardiac ejection fractions is only of limited value. In the future, an improvement will perhaps be obtained with tracers such as MIBI labelled with technetium 99m, which allow the simultaneous assessment of myocardial perfusion and the ventricular ejection fractions as well. The localisation of centres of infection, especially when intra-abdominal, remains difficult in intensive care patients. Isotopic imaging, especially the scintigraphies with labelled polynuclears, could allow in combination with conventional imaging techniques (computed tomography and 2 D echocardiography) to prevent from errors in diagnosis. An array of arguments is essential for ascertaining the presence of an abscess. Scintigraphies with leucocytes labelled with indium 111 or technetium 99m are qualified as having a sensitivity and a specificity greater than 90%. The conventional techniques of measurement of the cerebral blood flow (CBF) using xenon 133 require a special equipment or are invasive. Other cerebral tracers, such as cyclic amines (HMPAO) labelled with technetium 99m and administrable by i.v. route, allow the use of a standard tomo-gamma camera, and could be of help in various pathological conditions.(ABSTRACT TRUNCATED AT 400 WORDS)

Radioimmunoconjugates in the detection of infection and inflammation

Various nuclear medicine techniques are widely used to image foci of infection and inflammation. Among the relatively new radiopharmaceuticals for this purpose are radioimmunoconjugates such as labeled murine monoclonal antigranulocyte antibodies and labeled human polyclonal nonspecific immunoglobulin G. This article reviews some background information, mechanism of action, side effects, biodistribution, kinetics, results of clinical studies, and dosimetry of several radioimmunoconjugates both of murine monoclonal and human polyclonal origin. The efficacy of these agents has been demonstrated in a variety of clinical conditions. Radiolabeled immunoconjugates may emerge as convenient alternatives to the present technique of choice: in vitro blood cell labeling techniques with their inherent problems and risks.

Recent achievements in the development of radiolabeled monoclonal antibodies for diagnosis, therapy and biologic characterization of human tumors

Human tumors express antigenic sites that can serve as targets for radiolabeled monoclonal antibodies for diagnosis, therapy and biologic characterization of human tumors in vivo. Over the last decade, nearly 200 clinical trials have been performed which demonstrate that tumors can be detected with excellent sensitivity and specificity. Tumors which are otherwise occult, particularly for colorectal (anti-CEA and anti-TAG-72 antibodies) and ovarian cancer (anti-TAG-72 and anti-HMFG), are detected in a significant fraction of problem patients. Therapy using radiolabeled antibodies has been effective in lymphomas, leukemias and neuroblastomas, and is beginning to show promise in other solid tumors. Biologic characterization of tumors is likely to become more and more important in the future as monoclonal antibodies against oncogene products, such as her-2-neu, are developed. Development of new antibody forms through genetic engineering techniques, and the continual evolution toward higher resolution imaging instruments, such as PET and SPECT, will lead to further clinical improvements in cancer detection.