An ELISA uses which of the following reagents?
a. Enzyme-labeled anti-antibody
b. Radioactive anti-antibody
c. Source of complement
d. Enzyme-labeled antigen

Verified step by step guidance

1. Understand that ELISA (Enzyme-Linked Immunosorbent Assay) is a technique used to detect the presence of an antigen or antibody in a sample by using an enzyme-linked reagent that produces a measurable signal, usually a color change.
2. Recall that the key reagent in ELISA is an antibody or antigen that is linked to an enzyme, which acts as a reporter to generate a detectable signal after a substrate is added.
3. Identify that the enzyme-labeled reagent is typically an antibody (often called an anti-antibody when it binds to another antibody) rather than a radioactive label or complement source, as ELISA relies on enzymatic activity for detection.
4. Eliminate options that do not fit the ELISA principle: radioactive labels are used in radioimmunoassays, complement is involved in other immune assays, and enzyme-labeled antigen is less common than enzyme-labeled antibody in standard ELISA formats.
5. Conclude that the correct reagent used in ELISA is an enzyme-labeled anti-antibody, which binds to the target antibody and allows for enzymatic detection.

Key Concepts

Enzyme-Linked Immunosorbent Assay (ELISA)

ELISA is a biochemical technique used to detect the presence of an antigen or antibody in a sample by using an enzyme-linked antibody that produces a measurable color change. It relies on the specificity of antibodies to bind their target and an enzyme to generate a detectable signal.

Role of Enzyme-Labeled Antibodies

In ELISA, antibodies are conjugated to enzymes such as horseradish peroxidase or alkaline phosphatase. These enzyme-labeled antibodies bind specifically to the target antigen or antibody, and upon addition of a substrate, the enzyme catalyzes a colorimetric reaction indicating the presence of the target.

Difference Between Enzyme Labels and Radioactive Labels

ELISA uses enzyme labels rather than radioactive labels to detect binding events, making it safer and easier to handle. Radioactive labels are used in other assays like RIA (Radioimmunoassay), but ELISA specifically employs enzyme-linked reagents for signal generation.