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Well-Characterized Monoclonal Antibodies against Cell Wall Antigen of Aspergillus Species Improve Immunoassay Specificity and Sensitivity

Wei Hao,^1, Yu-Xian Pan,^1, Yan-Qing Ding,² Sha Xiao,³ Kai Yin,¹ Ya-Di Wang,¹ Li-Wen Qiu,¹ Qing-Lin Zhang,² Patrick C. Y. Woo,⁴ Susanna K. P. Lau,⁴ Kwok-Yung Yuen,⁴ and Xiao-Yan Che^1*

Center of Laboratory, Zhujiang Hospital, Southern Medical University, Guangzhou, China,¹ Department of Pathology, School of Basic Medical Science, Southern Medical University Guangzhou, China,² Department of Pathology, Zhujiang Hospital, Southern Medical University, Guangzhou, China,³ Department of Microbiology, The University of Hong Kong, Hong Kong Special Administrative Region, China⁴

Received 31 August 2007/ Returned for modification 10 October 2007/ Accepted 5 November 2007

The diagnosis of invasive aspergillosis (IA) based on the detection of Aspergillus galactomannan (GM) is complicated by the presence of cross-reactive GM epitopes in patient specimens. We have developed a novel and specific Aspergillus antigen-capture enzyme-linked immunosorbent assay (ELISA) by the selection of two well-characterized monoclonal antibodies from 17 candidate antibodies. The epitopes recognized by the monoclonal antibodies were present on the cell walls of the hyphae and the conidia of Aspergillus species, which were circulating or excreted as immunodominant antigens during the acute phase of IA established in the animal models. The detection of experimental Aspergillus-mediated antigenemia was suitably sensitive, and the sensitivity was comparable to that of a commercial GM detection ELISA kit (the Platelia Aspergillus assay). Moreover, the specificity of this assay was 100% when it was used to test 382 serum specimens and 120 urine specimens from healthy individuals. Cross-reactivity with other common opportunistic fungi, such as Penicillium and Candida species, and with purified GM protein derived from Aspergillus was not evident. Therefore, the chemical nature of the epitopes captured in this assay is most likely not associated with the GM structure, indicating that this newly developed Aspergillus antigen-capture ELISA is a promising tool for the diagnosis of IA without the risk of the false-positive results that are problematic with current GM antigen assays.

Published ahead of print on 21 November 2007.

Wei Hao and Yu-Xian Pan contributed equally to this work.