Imaging of systemic Candida albicans infections with a radioiodinated monoclonal antibody: Experimental study in the guinea pig

Guinea pigs intravenously infected with Candida albicans were scanned to evaluate the use of radioiodinated monoclonal antibodies (MAb) to fungal antigens for detecting tissue infection sites. A total of 18 infected and 8 uninfected animals were used. MAb and F(ab′) 2 fragments directed against cell wall glycoproteins of C. albicans were labeled with 131I. Another MAb directed against a Schistosoma mansoni glycoprotein was labeled with 125I and used as a nonspecific control. Radiolabeled MAbs were injected at a dose of 12.5 μg (500 kBq) per animal. Images were acquired 24 h later. Animals were then killed and the dissected organs were separately gamma-counted. The number of C. albicans colony forming units (cfu) per gram was determined in each organ. A clear relationship was found between the anatomic distributions of C. albicans and 131I. The biodistribution of 131I radioactivity associated with anti- Candida MAb was greater in infected animals than in healthy animals and increased with the number of cfu per g in each organ. The distribution was highly specific in animals with Candida endophthalmitis, a pathognomic feature of organ involvement during hematogenous dissemination. In contrast, the distribution of 125I radioactivity associated with the nonspecific MAb was similar in healthy and infected animals. In infected animals, it was totally independent of the intensity of fungal infection.