Abstract
The human response to invading fungi includes a series of events that detect, kill, or clear the fungi. If the metabolic host response is unable to eliminate the fungi, an infection ensues. Some of the host response’s metabolic events to fungi can be imaged with molecules labelled with radionuclides. Several important clinical applications have been found with radiolabelled biomolecules of inflammation. 18F-fluorodeoxyglucose is the tracer that has been most widely investigated in the host defence of fungi. This tracer has added value in the early detection of infection, in staging and visualising dissemination of infection, and in monitoring antifungal treatment. Radiolabelled antimicrobial peptides showed promising results, but large prospective studies in fungal infection are lacking. Other tracers have also been used in imaging events of the host response, such as the migration of white blood cells at sites of infection, nutritional immunity in iron metabolism, and radiolabelled monoclonal antibodies. Many tracers are still at the preclinical stage. Some tracers require further studies before translation into clinical use. The application of therapeutic radionuclides offers a very promising clinical application of these tracers in managing drug-resistant fungi.
Highlights
Fungal infections cause high morbidity and mortality, especially in immunocompromised patients [1]
We describe radionuclide-based positron emission tomography (PET) and singlephoton emission computed tomography (SPECT) imaging agents used in inflammation and their correlation to the events of host defence of fungi
This peptide is expected to accumulate in Aspergillus fumigatus and Candida albicans and bacteria to its SPECT counterpart, as the mechanism of uptake is the binding of the cationic peptide to the negative charge on the membrane of the microbe for both PET and SPECT tracers
Summary
Fungal infections cause high morbidity and mortality, especially in immunocompromised patients [1]. Once the host recognises the fungi, the receptor-pathogen interaction sets intracellular events that result in the formation of chemokines and cytokines that modulate inflammation. These chemokines and cytokines cause white blood cells to migrate to the infection site, leading to the phagocytosis of the fungi, and eventually to the killing and clearing of the fungi [2,5]. Anatomic-based imaging in infection often depends on structural changes that may not occur early in the sequence of the host’s reaction to the fungi. We describe radionuclide-based PET and SPECT imaging agents used in inflammation and their correlation to the events of host defence of fungi. Imaging is able to stage the infection, to detect occult or disseminated infection, to monitor antifungal therapy, and to provide prognostic information [10,11]
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