Which of the following indicates the presence of anti- DNase B activity in serum?

• A. Reduction of methyl green from green to colorless
• B. Clot formation when acetic acid is added
• C. Inhibition of red blood cell hemolysis
• D. Lack of change in the color indicator

Answer: (A)

The test is about a colorimetric DNase assay using methyl green as the indicator. Methyl green binds DNA and gives a green color. When DNase B is active, it digests the DNA, releasing the methyl green dye and causing the solution to fade to colorless. Observing this color change from green toward colorless signals DNase B–mediated digestion in the reaction, which, in this assay setup, is interpreted as the presence of anti-DNase B activity in the serum. In other words, the reduction of methyl green color reflects the readout you use to indicate anti-DNase B–related activity. The other options describe different reagents or outcomes not matching this specific colorimetric readout.