A 58-year-old asymptomatic woman comes to the office for a health checkup prior to starting volunteer work at a hospital. She has a history of hypothyroidism and takes levothyroxine. She does not use tobacco, alcohol, or illicit drugs. Her examination findings are unremarkable. During a laboratory test, her white blood cells are incubated with mycobacterial antigens. Compared to the control, a large amount of interferon-gamma is detected in her blood sample. Which of the following cell types is most directly responsible for this finding?

Question

A 58-year-old asymptomatic woman comes to the office for a health checkup prior to starting volunteer work at a hospital.  She has a history of hypothyroidism and takes levothyroxine.  She does not use tobacco, alcohol, or illicit drugs.  Her examination findings are unremarkable.  During a laboratory test, her white blood cells are incubated with mycobacterial antigens.  Compared to the control, a large amount of interferon-gamma is detected in her blood sample.  Which of the following cell types is most directly responsible for this finding?

Quizplus · Accepted Answer

Interferon-gamma (IFN-γ) activates macrophages, increases major histocompatibility complex expression, and promotes T helper 1 lymphocyte (Th1) differentiation. It is produced primarily by activated T lymphocytes and natural killer cells and is critical in immunity against viral and intracellular bacterial infections. IFN-γ release assays (IGRAs) test for latent tuberculosis infection (LTBI) by measuring the response of T lymphocytes when exposed to antigens unique to Mycobacterium tuberculosis. Similar to tuberculin skin tests (eg, purified protein derivative), IGRAs measure cell-mediated immunity. IGRAs have comparable sensitivity and specificity to tuberculin skin tests, but advantages include their lack of cross-reactivity to the Bacille Calmette-Guérin (BCG) vaccine and that a follow-up visit is not required. Neither skin tests nor IGRAs can be used to distinguish active tuberculosis from LTBI. (Choice A) B lymphocytes are the main cell type involved in the humoral immune system and the production of circulating antibodies. (Choices B and D) Basophils and antigen-presenting cells such as monocyte-derived macrophages interact with T cells to control the immune response but are not directly responsible for IFN-γ release. (Choices C and E) Eosinophils help eradicate parasitic infections (eg, helminths), whereas neutrophils are involved in the phagocytosis of bacteria and other pathogens. Educational objective: Interferon-gamma (IFN-γ) release assays test for latent tuberculosis infection by measuring the amount of IFN-γ released by T lymphocytes when exposed to antigens unique to Mycobacterium tuberculosis. __________ References: Gamma interferon release assays for detection of Mycobacterium tuberculosis infection. (http://www.ncbi.nlm.nih.gov/pubmed/24396134) Regulation of interferon-gamma during innate and adaptive immune responses. (http://www.ncbi.nlm.nih.gov/pubmed/17981204) Clinical application and limitations of interferon-gamma release assays for the diagnosis of latent tuberculosis infection. (http://www.ncbi.nlm.nih.gov/pubmed/21460320)

A 58-Year-Old Asymptomatic Woman Comes to the Office for a Health