Potential cross-reactivity of severe acute respiratory syndrome-associated coronavirus (SARS-CoV) nucleocapsid (N)-based IgG ELISA assay for plasma samples from HIV-1 positive intravenous drug users (IDUs).

to evaluate the specificity of the SARS-CoV N protein-based IgG ELISA assay for detection of immunoglobulin G (IgG) in plasma samples obtained from HIV-1 positive and HIV-1 negative intravenous drug users (IDUs). the SARS-CoV N gene was cloned into pQE-80L vector, and the constructs were transformed into Escherichia coli BL21. The 6x His-tagged N protein was expressed by inducing the bacterial cells with isopropyl-1-thio-D-galactopyranoside (IPTG) and purified by Ni-NTA affinity resin. The 6x His-tagged N protein was used as antigen for ELISA assay and evaluated for the serum samples from patients with SARS positive and the plasma samples from the HIV-1 positive and negative IDUs. all sera samples from patients with SARS positive were the ELISA positive (100% sensitivity). The ELISA assay yielded no positive results of the total 61 HIV-1 negative IDU samples (100% specificity) and two positive results of the total 68 HIV-1 positive IDU samples (97.06% specificity). the specificity of the SARS-CoV N protein-based IgG ELISA assay for the detection of the SARS-CoV N specific IgG in plasma samples from IDUs with HIV-1 positive is, therefore, questionable.