In immunofluorescence testing for anti-dsDNA antibodies, which organism is used as the substrate?

In immunofluorescence testing for anti-dsDNA antibodies, which organism is used as the substrate?

• A. Saccharomyces cerevisiae
• B. Escherichia coli
• C. Crithidia luciliae
• D. Bacillus subtilis

Answer: (C)

The key idea is using a substrate that presents double-stranded DNA in a way that anti-dsDNA antibodies can recognize specifically and without a lot of background noise. Crithidia luciliae fits this need because it has a kinetoplast, a distinct organelle containing a large amount of circular dsDNA that is not associated with histones. When serum with anti-dsDNA antibodies is added, these antibodies bind to that dsDNA in the kinetoplast, and a fluorescent secondary antibody reveals a bright, localized signal at the kinetoplast if the antibodies are present. This makes the test highly specific for anti-dsDNA antibodies. Saccharomyces cerevisiae (yeast) would present DNA within chromatin-bound nuclei, with histones and other nuclear proteins, which can create more background and less specific binding for anti-dsDNA antibodies. Bacteria like Escherichia coli and Bacillus subtilis lack the kinetoplast structure and present DNA in a different context, leading to less reliable and less specific detection of anti-dsDNA antibodies.

The key idea is using a substrate that presents double-stranded DNA in a way that anti-dsDNA antibodies can recognize specifically and without a lot of background noise. Crithidia luciliae fits this need because it has a kinetoplast, a distinct organelle containing a large amount of circular dsDNA that is not associated with histones. When serum with anti-dsDNA antibodies is added, these antibodies bind to that dsDNA in the kinetoplast, and a fluorescent secondary antibody reveals a bright, localized signal at the kinetoplast if the antibodies are present. This makes the test highly specific for anti-dsDNA antibodies.

Saccharomyces cerevisiae (yeast) would present DNA within chromatin-bound nuclei, with histones and other nuclear proteins, which can create more background and less specific binding for anti-dsDNA antibodies. Bacteria like Escherichia coli and Bacillus subtilis lack the kinetoplast structure and present DNA in a different context, leading to less reliable and less specific detection of anti-dsDNA antibodies.