What is the role of natural regulatory T cells?

Question 1 of 5

A. To activate potentially self-reactive T cells B. To suppress the activation of potentially self-reactive T cells C. To promote the activation of B cells D. To induce somatic hypermutation in B cells

Correct Answer: B

Rationale: Natural Treg cells suppress self-reactive T cells ; they don't activate , target B cells , or cause hypermutation .

Question 2 of 5

Individuals with defects in T cell development have a severe immunodeficiency disease called SCID (severe combined immunodeficiency disease). In these individuals, the absence of all T cells causes defects in both cell-mediated (T cell-based) and humoral (antibody-based) immune responses. The defect in antibody responses in SCID patients is due to:

A. The important role of T cells in regulating B cell development in the bone marrow B. The inter-dependence of T cells and B cells for the normal development of secondary lymphoid organs C. The absence of phagocytic cells needed for antibody-dependent pathogen clearance in SCID patients D. T follicular helper cells are critical for antibody responses

Correct Answer: D

Rationale: T follicular helper cells are critical for antibody responses; B-cell development is T-independent, organs form , phagocytes exist , B cells survive .

Question 3 of 5

Many different viruses encode proteins that function to down-regulate MHC class I expression on host cells following infection with the virus. This immune evasion mechanism allows the virus to hide from CD8 T lymphocytes that normally detect virus-infected cells by using their T cell antigen receptor to recognize viral peptides bound to MHC class I proteins on the surface of the infected cell. To counteract this immune evasion strategy, NK cells have:

A. Activating receptors that recognize MHC class I proteins B. A mechanism to secrete antiviral peptides C. Inhibitory receptors that recognize viral capsid proteins D. Activating receptors that recognize viral capsid proteins

Correct Answer: A

Rationale: NK cells use inhibitory MHC I receptors ; low MHC I activates them, not activating MHC or capsid (C/D) receptors.

Question 4 of 5

The TCR signaling module leading to transcription factor activation is dependent on the enzyme phospholipase-C-Î³ (PLC-Î³). The mechanism by which PLC-Î³ activates multiple transcription factors is by:

A. Generating two small second messengers that act on multiple target proteins in the T cell B. Directly cleaving inhibitory subunits of multiple transcription factors, thereby releasing the active transcription factors C. Generating two small second messengers that diffuse to the nucleus and activate transcription factors present there D. Generating two small second messengers that act as chaperones to promote nuclear localization of transcription factors

Correct Answer: A

Rationale: PLC-Î³ produces IP3 and DAG , activating transcription factors; not direct cleavage , nuclear diffusion , or chaperones .

Question 5 of 5

What substance, produced by virus-infected cells, diffuses to neighboring cells to help them fight a viral infection?

A. lysozyme B. interferon C. histamine D. interleukin-2

Correct Answer: B

Rationale: Interferon is produced by virus-infected cells and signals nearby cells to enhance antiviral defenses, unlike lysozyme (antibacterial), histamine (inflammation), or interleukin-2 (immune activation).

What is the role of natural regulatory T cells?

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