Skin testing is a useful diagnostic tool in disorders such as tuberculosis. Which statement is true?

Skin testing is a useful diagnostic tool in disorders such as tuberculosis. Which statement is true?

• A. Positive test depends on preformed antibody.
• B. Reactivity to a particular antigen may be transferred from one individual to another by sensitized lymphocytes.
• C. The intensity of the response directly reflects disease activity.
• D. The maximum response occurs immediately.

Answer: (B)

Skin testing shows that the body’s reaction is driven by cell-mediated immunity, specifically a delayed-type hypersensitivity reaction produced by sensitized T lymphocytes. The statement that reactivity to a particular antigen can be transferred from one person to another by sensitized lymphocytes is the best reflection of this: memory T cells that recognize the antigen can be moved to a different individual and, upon exposure to the antigen, generate the same delayed inflammatory response. This underlines that the test relies on T cells, not antibodies. The test’s positivity does not depend on preformed antibody, and the strength of the reaction does not directly measure current disease activity. Also, the maximum response does not occur immediately; it peaks about 48–72 hours after antigen exposure.

Skin testing shows that the body’s reaction is driven by cell-mediated immunity, specifically a delayed-type hypersensitivity reaction produced by sensitized T lymphocytes. The statement that reactivity to a particular antigen can be transferred from one person to another by sensitized lymphocytes is the best reflection of this: memory T cells that recognize the antigen can be moved to a different individual and, upon exposure to the antigen, generate the same delayed inflammatory response. This underlines that the test relies on T cells, not antibodies. The test’s positivity does not depend on preformed antibody, and the strength of the reaction does not directly measure current disease activity. Also, the maximum response does not occur immediately; it peaks about 48–72 hours after antigen exposure.