A purified protein from Mycobacterium tuberculosis is injected into a person’s skin. A hardened, red area develops around the injection site within 3 days.

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Identify the type of immune response described: a purified protein from Mycobacterium tuberculosis is injected intradermally, and a localized hardened, red area develops within 3 days. This suggests a delayed-type hypersensitivity reaction.

Recall that the test described is the Tuberculin Skin Test (TST), also known as the Mantoux test, which is used to detect prior sensitization to Mycobacterium tuberculosis.

Understand that the reaction is mediated by T cells (specifically Th1 cells) that recognize the protein antigen and recruit macrophages, leading to inflammation and induration (hardening).

Name the test based on this immunological principle: it is called the Tuberculin Skin Test or Mantoux test.

Summarize that the observed reaction is a classic example of a Type IV hypersensitivity reaction, which is cell-mediated and typically appears 48-72 hours after antigen exposure.

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Key Concepts

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

Tuberculin Skin Test (Mantoux Test)

The tuberculin skin test involves injecting a purified protein derivative (PPD) from Mycobacterium tuberculosis into the skin to detect prior exposure. A localized immune reaction causing redness and induration within 48-72 hours indicates a positive test, reflecting a cell-mediated immune response.

Delayed-Type Hypersensitivity (Type IV Hypersensitivity)

This immune response is mediated by T cells rather than antibodies and occurs 24-72 hours after antigen exposure. In the tuberculin test, sensitized T cells recognize the injected protein, releasing cytokines that recruit macrophages and cause localized inflammation and tissue hardening.

Cell-Mediated Immunity in Tuberculosis

Cell-mediated immunity is crucial for controlling Mycobacterium tuberculosis infection. Sensitized T helper cells activate macrophages to contain the bacteria, and this immune memory is the basis for the skin test reaction, indicating prior sensitization to the pathogen.

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Textbook Question

In an agglutination test, eight serial dilutions to determine antibody titer were set up: Tube 1 contained a 1:2 dilution; tube 2, a 1:4, and so on. If tube 5 is the last tube showing agglutination, what is the antibody titer?

a. 5

b. 1:5

c. 32

d. 1:32

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Textbook Question

Test used to detect the presence of antibodies in a patient’s serum.

a. Direct fluorescent antibody

b. Indirect fluorescent antibody

c. Rabies immune globulin

d. Killed rabies virus