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.