Detection of Urinary Excreted Fungal Galactomannan-like Antigens for Diagnosis of Invasive Aspergillosis

Abstract

Mortality associated with invasive aspergillosis (IA) remains high, partly because of delayed diagnosis. Detection of microbial exoantigens, released in serum and other body fluids during infection, may help timely diagnosis. In course of IA, Aspergillus galactomannan (GM), a well established polysaccharide biomarker, is released in body fluids including urine. Urine is an abundant, safely collected specimen, well-suited for point-of-care (POC) testing, which could play an increasing role in screening for early disease. Our main objective was to demonstrate GM antigenuria as a clinically relevant biological phenomenon in IA and establish proof-of-concept that it could be translated to POC diagnosis. Utilizing a novel IgM monoclonal antibody (MAb476) that recognizes GM-like antigens from Aspergillus and other molds, we demonstrated antigenuria in an experimental animal IA model (guinea pig), as well as in human patients. In addition, we investigated the chemical nature of the urinary excreted antigen in human samples, characterized antigen detection in urine by immunoassays, described a putative assay inhibitor in urine, and indicated means of alleviation of the inhibition. We also designed and used a lateral flow immunochromatographic assay to detect urinary excreted antigen in a limited number of IA patient urine samples. In this study, we establish that POC diagnosis of IA based on urinary GM detection is feasible. Prospective studies will be necessary to establish the performance characteristics of an optimized device and define its optimal clinical use.

Urine Galactomannan-to-Creatinine Ratio for Detection of Invasive Aspergillosis in Patients with Hematological Malignancies

“…After promising results in an animal model nearly 3 decades ago (4), only very recent pilot studies have indicated that GM detection in urine may be promising for IA screening in humans (5)(6)(7)(8). Besides important advantages, one of the potential major limitations of urine specimen testing is that GM dilutions in urine vary, thus influencing GM concentrations.…”

“…Besides important advantages, one of the potential major limitations of urine specimen testing is that GM dilutions in urine vary, thus influencing GM concentrations. Interestingly, previous studies on the diagnostic performance of urine GM determinations for IA did not take into account urine dilution, which may explain the inconsistent results (5)(6)(7)(8). Urine creatinine concentrations vary depending on water intake and are used to determine reliably the concentrations of various analytes in urine when 24-hour urine collection is not feasible.…”

“…First, noninvasive and easy sample collection may allow for home testing for urine GM in the future, once point-of-care (POC) tests have been developed. Second, urine GM testing, in contrast to serum testing, allows more frequent examination of large volumes, which may increase the sensitivity of the GM test (6,8,11). The diagnostic performance of urine GM testing was improved by calculation of the urine GM/creatinine ratio.…”

Biomarkers for Invasive Aspergillosis: The Challenges Continue

“…The feasibility of this approach has been demonstrated in a recent report that used a novel IgM monoclonal antibody (mAb476) that recognizes GM-like antigens from Aspergillus and other molds, together with a lateral flow immunochromatographic assay to detect urinary excreted antigen in IA patient urine samples [92]. However, it remains to be seen whether the time course of GM expression is compatible with early diagnosis and if standardized pretreatment is critical.…”

Long-Term Stability at −20°C of Aspergillus Galactomannan in Serum and Bronchoalveolar Lavage Specimens

“…Recently, several investigators developed lateral flow devices for detection of Aspergillus GM, to allow point-ofcare testing (3)(4)(5)(6)(7). Others have described monoclonal antibodies that recognize glycoproteins containing GM that may be useful for diagnostic tests based on detection of these antigens (8,9).…”