NAME IT 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.

Verified step by step guidance

1. Step 1: Understand the context of the problem. This scenario describes a common test used in microbiology and immunology, specifically related to Mycobacterium tuberculosis.
2. Step 2: Identify the test being described. The test is known as the Tuberculin Skin Test (TST) or Mantoux test, which is used to determine if someone has been exposed to the bacteria that cause tuberculosis.
3. Step 3: Recognize the immune response involved. The development of a hardened, red area is due to a delayed-type hypersensitivity reaction, which is a cell-mediated immune response.
4. Step 4: Explain the mechanism. When the purified protein derivative (PPD) from Mycobacterium tuberculosis is injected, it is recognized by T-cells in individuals who have been previously sensitized to the bacteria, leading to an inflammatory response.
5. Step 5: Discuss the interpretation. The size of the induration (hardened area) is measured to determine if the test is positive, indicating prior exposure to the bacteria, either through infection or vaccination with BCG.

Key Concepts

Mycobacterium tuberculosis

Mycobacterium tuberculosis is the bacterium that causes tuberculosis (TB), a serious infectious disease primarily affecting the lungs. It is a slow-growing, aerobic organism that can evade the immune system, leading to chronic infection. Understanding its biology and pathogenic mechanisms is crucial for comprehending how it triggers immune responses in the host.

Delayed-type hypersensitivity (DTH)

Delayed-type hypersensitivity is an immune response mediated by T cells, typically occurring 24 to 72 hours after exposure to an antigen. In the context of the question, the injection of a purified protein from Mycobacterium tuberculosis elicits a DTH reaction, characterized by a localized inflammatory response, which manifests as a hardened, red area at the injection site.

Tuberculin skin test (TST)

The tuberculin skin test, also known as the Mantoux test, is a diagnostic tool used to determine if a person has been exposed to the tuberculosis bacterium. It involves intradermal injection of tuberculin, a purified protein derivative, and the subsequent assessment of the skin reaction. A positive result indicates prior exposure or infection, reflecting the immune system's response to the antigen.