Textbook Question
When antigen and antibodies combine, maximal precipitation occurs when:
a. Antigen is in excess
b. Antibody is in excess
c. Antigen and antibody are at equivalent concentrations
d. Antigen is added to the antibody
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20. Adaptive Immunity
Outcomes of Antibody Binding to Antigen
2:26 minutesProblem 8
Textbook Question
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 guidance1
Understand that ELISA (Enzyme-Linked Immunosorbent Assay) is a technique that uses an enzyme-linked antibody or antigen to detect the presence of a specific target molecule, usually an antigen or antibody, in a sample.
Recall that the key reagent in ELISA is an enzyme-labeled antibody (or sometimes antigen) that binds specifically to the target, allowing detection through a color change when a substrate is added.
Evaluate each option: (a) Enzyme-labeled anti-antibody fits the description of the enzyme-linked reagent used in ELISA to detect the target antibody or antigen.
(b) Radioactive anti-antibody is used in radioimmunoassays, not ELISA, so it is not the correct reagent for ELISA.
(c) Source of complement is related to complement fixation tests, not ELISA, so it is not relevant here.
(d) Enzyme-labeled antigen can be used in some ELISA formats, but the most common and classic ELISA uses enzyme-labeled antibodies rather than antigens.
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Video duration:
2mKey Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Enzyme-Linked Immunosorbent Assay (ELISA)
ELISA is a laboratory technique used to detect and quantify antigens or antibodies by using an enzyme-linked antibody that produces a measurable color change. It relies on the specific binding between an antigen and an antibody, with the enzyme acting as a reporter to generate a detectable signal.
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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, allowing quantification of the target molecule.
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Difference Between Enzyme and Radioactive Labels
ELISA uses enzyme labels rather than radioactive labels to detect binding events. Enzyme labels are safer, more stable, and produce visible color changes, whereas radioactive labels require special handling and detection equipment. This distinction is key to understanding why ELISA uses enzyme-labeled antibodies instead of radioactive ones.
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