Ch. 18 - Practical Applications of Immunology

Tortora - Microbiology: An Introduction 14th Edition

Tortora14th EditionMicrobiology: An IntroductionISBN: 9780138200398Not the one you use?Change textbook

Tortora 14th Edition

Ch. 18 - Practical Applications of Immunology

Problem 6

Chapter 18, Problem 6

Label components of the direct and indirect ELISA tests in the following situations. Which test is direct? Which test provides definitive proof of disease?

Verified step by step guidance

Step 1: Understand the difference between direct and indirect ELISA. In a direct ELISA, the antigen is immobilized on the plate, and a labeled antibody specific to the antigen binds directly to it. In an indirect ELISA, the antigen is also immobilized, but an unlabeled primary antibody binds to the antigen first, followed by a labeled secondary antibody that binds to the primary antibody.

Step 2: For both ELISA types, start by drawing a solid horizontal line to represent the surface of the microtiter plate well where the antigen is attached.

Step 3: In the direct ELISA diagram, label the antigen bound to the plate surface, then draw and label a single enzyme-linked antibody that binds directly to the antigen.

Step 4: In the indirect ELISA diagram, label the antigen bound to the plate surface, then draw and label the primary antibody that binds to the antigen, followed by a secondary antibody that is enzyme-linked and binds to the primary antibody.

Step 5: To determine which test is direct, identify the one with only one antibody binding directly to the antigen. For definitive proof of disease, consider that indirect ELISA is generally more sensitive and specific because it uses two antibodies, reducing false positives and providing stronger evidence of the presence of antibodies against the antigen.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Direct ELISA

Direct ELISA involves an antigen immobilized on a surface and a labeled antibody that binds directly to the antigen. It is simpler and faster but less specific because only one antibody is used. This test detects the presence of antigens in a sample.

Indirect ELISA

Indirect ELISA uses an antigen coated on a surface, a primary antibody specific to the antigen, and a labeled secondary antibody that binds to the primary antibody. This method is more sensitive and allows amplification of the signal, making it useful for detecting antibodies in a sample.

Definitive Proof of Disease in ELISA

Definitive proof of disease typically comes from detecting antibodies specific to a pathogen, indicating an immune response. Indirect ELISA is often more reliable for this because it detects antibodies, confirming exposure or infection, whereas direct ELISA detects antigens which may not always confirm active disease.

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Textbook Question

Use the following choices to answer questions 4 and 5:

a. Anti-Brucella

b. Brucella

c. Substrate for the enzyme

Which item is from the patient in an indirect ELISA test?

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Textbook Question

How are monoclonal antibodies produced?

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Textbook Question

Explain the effects of excess antigen and antibody on the precipitation reaction. How is the precipitin ring test different from an immunodiffusion test?

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Textbook Question

In an immunodiffusion test, a strip of filter paper containing diphtheria antitoxin is placed on a solid culture medium. Then bacteria are streaked perpendicular to the filter paper. If the bacteria are toxigenic,

a. The filter paper will turn red

b. A line of antigen–antibody precipitate will form

c. The cells will lyse

d. The cells will fluoresce

e. None of the above

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Textbook Question

Use the following choices to answer questions 7–9.

a. Direct fluorescent antibody

b. Indirect fluorescent antibody

c. Rabies immune globulin