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By Dr. Jacqueline Gosink, EUROIMMUN AG, Germany

INTRODUCTION An innovative technology based on the classic indirect immunofluorescence test (IIFT) is driving the rapid introduction of newly identified autoantibody parameters into routine laboratory diagnostics. In the new assay method, transfected cells are used for the first time as antigen substrates in IIFT to provide monospecific detection of antibodies. Cell-based IIFT systems represent an effective alternative to ELISA and immunoblot, especially for applications where these methods cannot, for various reasons, be deployed. The novel technology has already enriched various diagnostic areas, in particular autoimmune disease diagnostics.


A NEW TECHNOLOGY In cell-based immunoassays, the DNA coding for a particular antigen is inserted into a plasmid, which is then introduced into cultured cells by transfection (figure 1). The transfected cells expressing the target antigen are employed directly as a substrate for antibody detection by classic indirect immunofluorescence. The IIFT procedure consists of two simple incubation steps (figure 1). During the first incubation, specific antibodies from patient samples bind to the corresponding antigens in the substrate. In the second step, the bound antibodies are detected using a fluorescein-labelled secondary antibody. Results are visualised

by fluorescence microscopy. Compared to tissue substrates traditionally used in IIFT, which contain a myriad of different antigens and sometimes require specialist knowledge to interpret, transfected cells are easy to evaluate.

SIGNIFICANT ADVANTAGES In contrast to ELISA and immunoblot, which are based on purified antigens coupled to a solid phase, cell-based assays employ antigens expressed in vivo. This means that the technology is suitable in particular for antigens that are difficult to isolate or purify. For example, if an antigen is embedded in a membrane, the aggressive methods required to isolate it can also

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