Evaluating the Potential of Galactosaminogalactan as a Diagnostic Target for Invasive Aspergillosis

Early diagnosis of invasive aspergillosis (IA) is critical for the initiation of effective antifungal therapy. Currently, detection of galactomannan (GM), a secreted fungal glycan, is the most used culture-independent diagnostic test for IA. However, limitations in the sensitivity and specificity of this test have led to interest in identifying other target molecules. Galactosaminogalactan (GAG), a polysaccharide cell wall component secreted by Aspergillus hyphae, is a potential diagnostic marker for IA.

To evaluate the utility of GAG as a diagnostic target, we generated a monoclonal antibody against GAG (mAb 1D1), established a GAG enzyme-linked immunosorbent assay (ELISA), evaluated its cross-reactivity with other respiratory pathogens, and compared the performance of the GAG detection ELISA with GM antigen detection in both an in vivo mouse model and human samples from patients with pulmonary aspergillosis.

The GAG ELISA demonstrated strong reactivity with culture supernatants from Aspergillus fumigatus and Aspergillus flavus but limited reactivity with culture supernatants of other Aspergillus spp. and non-Aspergillus filamentous fungi. In a mouse model of IA, GAG was detected in lung tissue, serum, bronchoalveolar lavage fluid (BALF), and urine samples. Although GAG was detected by mAb 1D1 staining of Aspergillus hyphae in infected human lung tissue samples, it was not detectable in the serum, BALF, and urine of patients with pulmonary aspergillosis.

Further studies are required to determine whether the failure to detect GAG in the serum, BALF, and urine of patients with pulmonary aspergillosis is due to absence or low GAG levels or other reasons.